Neuroimaging in Neurogenic Communication Disorders

By Kostas Konstantopoulos and Dimitrios Giakoumettis

Neuroimaging in Neurogenic Communication Disorders provides a comprehensive review of cases utilizing neuroimaging in neurogenic communication disorders. Basic knowledge of neuroanatomy and medical conditions related to these speech and language disorders are discussed. Each case study includes information on neuroanatomy, case presentation, neuroimaging, differential diagnosis, and final diagnosis. This book is written for medical students, practitioners and researchers in neuroscience and speech language pathology.

Neurogenic communication disorders are caused by damage to the central or peripheral nervous system. This damage can be caused by Parkinson’s disease, stroke, dementia, traumatic brain injury, brain tumors, and other neurologic disorders and causes issues such as aphasia, dysarthria and apraxia.

• Focuses on neuroimaging in acquired neurogenic communication disorders like apraxia, dysarthria and aphasia
• Covers basic neuroanatomy as related to speech and pathology
• Includes cases organized by anatomical entities involved in lesions

• Language: English
• Publisher: Academic Press
• Release date: Jun 17, 2023
• ISBN: 9780128242018

Kostas Konstantopoulos

Dr. Kostas Konstantopoulos is an Associate Professor and Chair of the Speech Therapy Department at the University of Peloponnese. He has 7 years teaching experience for courses on neurogenics and acquired disorders of speech/language, cognitive rehabilitation and neuroanatomy. He has 14 years of clinical experience in speech therapy for neurologic patients, specifically those exhibiting acquired neurogenic disorders and diagnosed with Multiple Sclerosis, Cerebellar Ataxia, Parkinson’s Disease and Huntington’s Disease. He’s a full member of many professional societies including the British Neuroscience Association, the European Association of Parkinson’s Disease, the Movement Disorders Society, and the International Neuropsychological Society. He has published and reviewed for many scientific journals, and is co-author of “Neuroanatomy and Neurophysiology for Speech and Hearing Sciences” (2018)

Book preview

Neuroimaging in Neurogenic Communication Disorders

Kostas Konstantopoulos

Speech Therapy Department, University of the Peloponnese, Kalamata, Greece

Dimitrios Giakoumettis

Senior Clinical Fellow in Neurosurgery, Queen’s Hospital, Romford, London, United Kingdom

Table of Contents

Cover image

Title page

Copyright

Dedications

Contributors

Preface

Acknowledgments

Abbreviations

Chapter 1. Basic knowledge on neuroanatomy and neurophysiology of the central nervous system

Gross anatomy of the brain

Cerebral hemispheres

Basal ganglia and diencephalon

Brainstem

Cerebellum

White matter—fiber tracts

Neural tracts—pathways

Vasculature and blood supply of the brain

Chapter 2. Basic principles of neuroimaging

Computed tomography

Magnetic resonance imaging

Angiography

Other imaging studies

Chapter 3. Cerebral organization for speech/language and neuroanatomy of speech/language disorders

Historical aspects of the theory of cerebral organization for speech and language

Recent advances in the neuroanatomy of speech and language

Speech and language disorders

Neuroanatomical areas involved in speech and language

White matter fiber tracts involved in speech and language

Speech and language symptomatology as related to brain areas and white matter fiber tracts

Chapter 4. Clinical cases in neurovascular diseases and traumatic brain injury

Clinical case 1

Clinical case 2

Clinical case 3

Clinical case 4

Clinical case 5

Clinical case 6

Clinical case 7

Clinical case 8

Clinical case 9

Clinical case 10

Clinical case 11

Clinical case 12

Clinical case 13

Clinical case 14

Clinical case 15

Clinical case 16

Clinical case 17

Clinical case 18

Clinical case 19

Clinical case 20

Clinical case 21

Clinical case 22

Clinical case 23

Clinical case 24

Clinical case 25

Clinical case 26

Clinical case 27

Clinical case 28

Clinical case 29

Clinical case 30

Clinical case 31

Clinical case 32

Clinical case 33

Clinical case 34

Clinical case 35

Clinical case 36

Clinical case 37

Clinical case 38

Clinical case 39

Clinical case 40

Clinical case 41

Clinical case 42

Clinical case 43

Clinical case 44

Clinical case 45

Chapter 5. Clinical cases on functional neurosurgery and motor speech disorders

Clinical case 46

Clinical case 47

Clinical case 48

Clinical case 49

Clinical case 50

Clinical case 51

Clinical case 52

Clinical case 53

Clinical case 54

Clinical case 55

Chapter 6. Clinical cases in pediatric neurosurgery

Clinical case 56

Clinical case 57

Clinical case 58

Clinical case 59

Clinical case 60

Clinical case 61

Clinical case 62

Clinical case 63

Chapter 7. Clinical cases in neuro-oncology

Clinical case 64

Clinical case 65

Clinical case 66

Clinical case 67

Clinical case 68

Clinical case 69

Clinical case 70

Clinical case 71

Clinical case 72

Clinical case 73

Clinical case 74

Clinical case 75

Clinical case 76

Clinical case 77

Clinical case 78

Clinical case 79

Clinical case 80

Clinical case 81

Clinical case 82

Clinical case 83

Clinical case 84

Clinical case 85

Clinical case 86

Clinical case 87

Clinical case 88

Clinical case 89

Clinical case 90

Clinical case 91

Clinical case 92

Clinical case 93

Clinical case 94

Clinical case 95

Clinical case 96

Clinical case 97

Clinical case 98

Clinical case 99

Clinical case 100

Glossary

Index

Copyright

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Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

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Dedications

The authors of this textbook want to dedicate this book to the medical students, young doctors, and speech language pathology students who committed their lives to the patient's care and quality of life. KK wishes to dedicate this book to Elliana, the fellow life traveler, and his children, John, Evangelos, Thalia, and Philip. Their intriguing questions made him a wiser person. DG wishes to dedicate this book to his wife Evangelia and his two sons, Antonios-Stylianos and Meletios-Marios, for their patience and love. They keep my dreams alive and help me improve. They deserve the world and the world them. Special thanks to the rest of my family, parents (Antonios, Evangelia), brother (Georgios), and sister (Anastasia), who endlessly and actively support every step. I wouldn't be the man I am today without them.

Contributors

Argyro Chondrozoumaki,     401 General Military Hospital, Athens, Greece

Oliver Ganslandt,     Klinikum Katharinenhospital, Stuttgart, Germany

Georgios Giakoumettis,     AHEPA University Hospital, Thessaloniki, Greece

Nikolaos Haliasos,     Queen's Hospital, Romford, United Kingdom

Lauren Harris,     Queen's Hospital, Romford, United Kingdom

Vasiliki Kalliri,     Department of Neurosurgery, University Hospital Heidelberg, Heidelberg, Germany

Hu-Liang Low,     Queen's Hospital, Romford, United Kingdom

Jacob Low,     Cambridge Institute, University of Cambridge, Cambridge, United Kingdom

Emilia Michou

GI Sciences, School of Medical Sciences, Salford Royal Hospital, University of Manchester, Manchester, United Kingdom

Speech Language Pathology, University of Patras, Patras, Greece

Rabeeia Parwez,     Queen's Hospital, Romford, United Kingdom

Preface

This textbook provides medical students, speech and language pathology students, and any young physician or speech-language pathologist with clinical knowledge based on real patients' cases. It is the first of its kind. It replicates daily clinical practice in the neurosurgical department of large hospitals. It is written by a speech-language pathologist (Dr. Konstantopoulos) with 20+ years of clinical experience in neurogenic communication disorders and a neurosurgeon (Dr. Giakoumettis) who has operated in three countries.

This textbook intends to help readers enhance their clinical skills. They will be able to recognize lesions on neuroimaging, read their symptoms regarding language and speech, and deepen their knowledge about assessment and therapy.

Each patient is followed from the day of hospital admission to the referral to the neurosurgical department including the assessment by the speech-language pathologist. Broad categories of communication disorders are explained from the theoretical and practical perspectives of adult and pediatric patients. These include aphasia, apraxia, dysarthria, and cognitive-communication disorders. Tumors, ischemia, hemorrhage, and neurodegenerative diseases (based on relevant neuroimaging) are covered. A few cases without language/speech symptomatology are also included to show the reader the limits of language/speech areas in the human brain.

Questions are incorporated into each clinical case to encourage the reader to think about medical conditions and language/speech. The questions are included in the body of the text, following the logic of the working physician when dealing with a specific patient, enhancing the student's problem-solving ability. Each clinical case is self-contained. Specific questions are aimed at medical students, young doctors, residents, or young neurosurgeons (e.g., to classify tumors), while others are aimed at students or young speech-language pathologists (e.g., evidence-based speech therapy methods in conduction aphasia).

The questions are numbered (1–3) based on difficulty:

Grade 1 question=requires some knowledge.

Grade 2 question=requires expansion of knowledge through the literature.

Grade 3 question=requires detailed research of the literature.

The authors aim to provide basic knowledge about anatomy, neuroimaging, and the neuroanatomy of speech and language. Three chapters at the start (Chapters 1–3) help the reader understand the clinical cases provided in the following chapters (Chapters 4–7).

Chapter 1 discusses basic neuroanatomy and neurophysiology of the central nervous system, including the gross anatomy of the brain, the cerebral hemispheres, the subcortical structures, the brainstem, the cerebellum, white matter fiber/neural tracts, and the blood supply of the brain.

Chapter 2 introduces the basic principles of neuroimaging and the main neuroimaging methods. It covers the physics, applications, and interpretation of computed tomography (CT), magnetic resonance imaging (MRI), and angiography.

Chapter 3 reviews the neuroanatomy of language/speech, including the cortical and subcortical areas related to human communication. This chapter introduces terms such as aphasia, apraxia of speech, and dysarthria. It discusses specific brain areas and the white matter pathways involved in language/speech symptomatology. Speech symptoms, for example, paraphasias, are explained based on specific lesions in the human brain, to help the reader understand the complexity of the network of structures involved in aphasia, apraxia, or dysarthria.

Chapter 4 (Clinical Cases in Neuro-vascular diseases and Traumatic Brain Injury) includes 45 clinical cases on traumatic brain injury (1–11 clinical cases), ischemic stroke (12–27 clinical cases), and hemorrhagic stroke (28–45 clinical cases).

Chapter 5 (Clinical cases in functional neurosurgery and motor speech disorders) includes 10 clinical cases (46–55) regarding functional neurosurgery (deep brain stimulation) and motor speech disorders such as multiple sclerosis, Parkinson's disease, and myasthenia gravis.

Chapter 6 (Clinical cases and neuroimaging in pediatric neurosurgery) includes neuroimaging of 8 pediatric neurosurgically managed clinical cases (56–63) presenting with aphasia or dysarthria.

Chapter 7 includes 37 clinical cases (64–100) exhibiting different types of tumors (e.g., meningiomas, glioblastomas, astrocytomas, etc.).

This textbook is international, with contributions from the United Kingdom, Germany, Belgium, and Greece. The enthusiasm of the contributors allowed us to complete this textbook. We hope you enjoy and learn from this work. Please feel free to contact us with any feedback to allow us to refine this text for future editions.

Acknowledgments

(1) Hu-Liang Low, Senior Consultant Neurosurgeon, Head of Functional Neurosurgery, Queen's Hospital, Rom Valley Way, Romford, United Kingdom

(2) Nikolaos Haliasos, MD, FRCS, MSc, Consultant Neurosurgeon, and Academic Lead, Queen's Hospital, Rom Valley Way, Romford, United Kingdom

(3) Prof. Dr. Oliver Ganslandt, Medical Director Neurosurgical Clinic, Klinikum Katharine Hospital, Stuttgart, Germany

(4) Dr. Med. Vasiliki Kalliri, Consultant Neurosurgeon, Department of Neurosurgery, University Hospital Heidelberg, Germany

(5) Lauren Harris, MD, Senior Registrar, Queen's Hospital, Rom Valley Way, Romford, United Kingdom

(6) Georgios Giakoumettis, BSc, Physics, MSc Medical Physics, Senior Medical Physicist, AHEPA University Hospital, Thessaloniki, Greece

(7) Emilia Michou, PhD, CertMRCSLT, Honorary Fellow, GI Sciences, School of Medical Sciences, Salford Royal Hospital, University of Manchester, Assistant Professor, Speech Language Pathology, University of Patras

(8) Rabeeia Parwez, MD, Senior House Officer, Queen's Hospital, Rom Valley Way, Romford, United Kingdom

(9) Argyro Chondrozoumaki, MD, MSc, Neurosurgeon, Military Doctor, 401 General Military Hospital

(10) Jacob Low, MD, Research Fellow, Cancer Research, Cambridge Institute, University of Cambridge, United Kingdom

(11) Dr. Michel Triffaux, Consultant Neurosurgeon, Clinical Director Neurosurgery, CHWAPI Hospital, Tournai, Belgium

(12) Dr. Triantafyllos Bouras, Consultant Neurosurgeon, CHWAPI Hospital, Tournai, Belgium

Abbreviations

AAC    Augmentative and Alternative Communication

ACA    Anterior cerebral artery

ACE    Angiotensin-Converting Enzyme

AChA    Anterior choroidal artery

ACOM or Acomm    Anterior communicating artery

ADC    Apparent Diffusion Coefficient

ADEM    Acute Disseminated Encephalomyelitis

AFP    Alpha-Fetoprotein

AHA/ASA    American Heart Association/American Stroke Association

AICA    Anterior inferior cerebellar artery

ALK    Anaplastic Lymphoma Kinase

AMPK    Amp-Activated Protein Kinase

AMR    Alternating Motion Rate

ASA    American Society of Anesthesiologists

ASHA    American Speech and Hearing Association

ATLS    Advanced Trauma Life Support

ATRT    Atypical Rhabdoid Tumors

BARS    Brief Ataxia Rating Scale

BPM    Beats per minute

BRAF    B-Raf Human Gene

BSG    Brainstem Glioma

CAA    Cerebral Amyloid Angiopathy

CBTRUS    Central Brain Tumor Registry of the United States

CCA    Common carotid artery

CCNU    Cyclonexyl-Chloroethyl-Nitrosourea, Lomustine

Cho    Choline

CM    Cavernous Malformation

CNS    Central Nervous System

CPA    Cerebellopontine Angle

Cr    Creatinine

CRP    C-Reactive Protein

CSF    Cerebrospinal Fluid

CT    Computed Tomography

CTA    Computed Tomography Angiography

DC    Decompressive Craniectomy

DDK    Diadochokinesis

DECIMAL    Decompressive Craniectomy in Malignant MCA Infarction

DECRA    Decompressive Craniectomy

DESTINY    Decompressive Surgery for the Treatment of Malignant Infarction of the Middle Cerebral Artery

DIPG    Diffuse Intrinsic Pontine Glioma

DKA    Diabetic Ketoacidosis

DTI    Diffusion Tensor Imaging

DWI    Diffusion-Weighted Imaging

EANO    European Association of Neuro-oncology

ECA    External carotid artery

ECG    Electrocardiogram

ECOG    Eastern Cooperative Oncology Group

EGFR    Epidermal Growth Factor Receptor

ESO    European Stroke Organization

ETOH    Ethanol

EVD    External Ventricular Drain

F.A.S.T.    Face, Arms, Speech, Time

FBC    Full Blood Count

FLAIR    Fluid Attenuated Inversion Recovery

FSH    Follicle-Stimulating Hormone

GCT    Germ Cell Tumors

Gy    Gray

HAMLET    Hemicraniectomy after Middle Cerebral Artery Infarction with Life-Threatening Edema Trial

HCT    Hematocrit

HeADDFIRST    Hemicraniectomy and Durotomy upon Deterioration from Infarction-Related Swelling Trial

HGB    Hemoglobin

ICA    Internal carotid artery

ICARS    International Cooperative Ataxia Rating Scale

ICF    International Classification of Functioning, Disability, and Health

ICH    Intracerebral Hemorrhage

ICP    Intracranial Pressure

IDH    Isocitrate Dehydrogenase

IOPI    Iowa Oral Performance Instrument

IPGG    International PCNSL Collaborative Group

IVH    Intraventricular Hemorrhage

LAST    Language Screening Test

LDH    Lactate Dehydrogenase

LH    Luteinizing Hormone

LHD    Left Hemisphere Damage

MB    Medulloblastoma

MCA    Middle Cerebral Artery

MDT    Multidisciplinary Team

MFG    Middle Frontal Gyrus

MGMT    O-6-Methylguanine-DNA Methyltransferase

MLF    Medial Longitudinal Fasciculus

MRA    Magnetic Resonance Angiography

MRI    Magnetic Resonance Imaging

MRS    Magnetic Resonance Spectroscopy

NAA    N-Acetyl Aspartate

NCCN    National Comprehensive Cancer Network

NIHSS    National Institute of Health Stroke Scale

PCA    Posterior cerebral artery

PCNSL    Primary CNS Lymphoma

PCOM or Pcomm    Posterior communicating artery

PCV    Procarbazine, Lomustine, and Vincristine

PICA    Posterior Inferior Cerebellar Artery

PLAP    Placental Alkaline Phosphatase

PML    Progressive Multifocal Leukoencephalopathy

PPS    Post-Poliomyelitis Fatigue Syndrome

PSOM    Pediatric Stroke Outcome Measure

PVC    Premature Ventricular Contraction

RAP    Reducing Aphasic Perseveration

RAVLT    Rey Auditory-Verbal Learning Test

RBC    Red Blood Cells

RHD    Right Hemisphere Damage

RPA    Recursive Partitioning Analysis

RPD    Rapidly Progressive Dementias

SAH    Subarachnoid Hemorrhage

SARA    Scale for the Assessment and Rating of Ataxia

SCA    Superior cerebellar artery

SCAFI    SCA Functional Index

SFA    Semantic Feature Analysis

SHH    Sonic Hedgehog Gene

SMR    Sequential Motion Rate

T1WI    T1-Weighted Image

TOF    Time of Flight

tPA    Tissue Plasminogen Activator

TSC1/TSC2    Tuberous Sclerosis 1/Tuberous Sclerosis 2 Gene

TSH    Thyroid-Stimulating-Hormone

TWA    Treatment of Wernicke's Aphasia

UUMN    Unilateral Upper Motor Neuron

VCR    Vincristine

VFSS    Videofluoroscopy

VPMC    Ventral Premotor Cortex

WBC    White Blood Cells

WFNS    World Federation of Neurological Societies

WHO    World Health Organization

WNT    Wingless/Integrated Gene

β-hCG    Β-Human Chorionic Gonadotropin

Chapter 1: Basic knowledge on neuroanatomy and neurophysiology of the central nervous system

Abstract

Neuroanatomy and neurophysiology are the basic knowledge that a neuroscientist must master in order to study the brain and its function. This chapter describes the topography and function of the central nervous system and presents the necessary anatomical landmarks to further understand the cases in the book. The anatomy and physiology presented are the established knowledge, and no new knowledge is introduced. The gross anatomy of the central nervous system is presented, and thereafter the structures of the brain are analyzed. The five classical parts of the brain (telencephalon, diencephalon, mesencephalon, metencephalon and myelencephalon) are described, and each part is presented separately. The cerebral hemispheres, the lobes, the gyri and the sulci are mainly analyzed, as their anatomical knowledge explains the majority of the cases. The function of each lobe, the white matter tracts, and the neural pathways are also approached. Finally, this chapter elucidates the brain's blood supply, i.e., the arteries and the veins.

Keywords

Brain; Central nervous system; Cerebrum; Neuroanatomy; Neurophysiology; Parenchyma

Gross anatomy of the brain

Divisions of the brain

The brain can be divided either in a topographic manner or according to its embryological origin. Therefore, the brain has three main parts, the cerebral hemispheres, the brainstem, and the cerebellum. However, due to the fact that different parts of the brain have different embryological origins, an embryological division shows that the brain consists of five parts. The first part is the telencephalon, which comprises the cerebral hemispheres, the brain nuclei, the commissures, and the lateral ventricles. The second part is the diencephalon, which consists of the thalamus, the hypothalamus, the epithalamus, the metathalamus, and the third ventricle. The third part is the mesencephalon, which includes the midbrain, the quadrigeminal, the cerebral peduncles, and the aqueduct. The fourth part is the metencephalon (pons, cerebellum, a portion of the fourth ventricle), and the fifth part is the myelencephalon, which includes the medulla oblongata, and a portion of the fourth ventricle. ¹ , ²

Meninges and ventricles

The brain is surrounded by three protective layers known collectively as the meninges. These are from superficial to deep, the dura mater, the arachnoid mater, and pia mater. The first comprises two leaflets, the internal and the external layer, which in certain places are separated to create the venous sinus of the brain. The falx cerebri, the tentorium, the falx cerebelli, and the diaphragm of the pituitary are parts of the dura mater. The blood supply of the dura mater comes from the meningeal arteries (anterior, middle, posterior meningeal artery, and the meningeal branches of the spinal and occipital artery). The middle meningeal veins drain blood from the meninges. The innervation of the dura mater is complicated and comes from two cranial nerves (trigeminal nerve, vagus nerve), three peripheral nerves (the first three cervical nerves), and the sympathetic system for the cervical section of the dura.

The arachnoid mater lies underneath the dura mater, and in between is the subdural space. The arachnoid mater is attached to the underlying pia mater and between is the subarachnoid space, which is enlarged in certain places forming the cisterns. The arachnoid mater gives rise to the arachnoid villi where the drainage of the cerebrospinal fluid into the venous system happens. The arachnoid mater does not have any vasculature, and its innervation comes from three cranial nerves (trigeminal, facial, and accessory nerve).

The pia mater lies over the brain and dives within the sulci. It is the basic element of the choroid plexus and forms sheaths around the cranial nerves and vessels. It has no blood supply, but it contains some of the cerebral vessels. Its innervation comes from the sympathetic chain and meningeal branches of the cranial nerves.

The ventricular system of the brain are cavities in which the cerebrospinal fluid is produced and channeled to the rest of the nervous system. There are four ventricles, the two lateral ventricles, the third ventricle, and the fourth ventricle. They communicate between themselves and the subarachnoid space via foramen. The lateral ventricles are separated by the septum pellucidum, and they communicate with the third ventricle via the foramen of Monroe. The third ventricle communicates with the fourth ventricle through the aqueduct of Sylvius. Finally, the fourth ventricle channels the cerebrospinal fluid to the subarachnoid space through the foramen of Magendi and Luschka and to the medulla oblongata through the central canal.

Gray and white matter of the brain

Gray matter contains the bodies of the neuron cells, whereas the white matter contains the myelinated axons of the neuron cells.

Cerebral hemispheres

The cerebral hemisphere surface comprises gyri, fissures, and sulci, which are invaginations of the cerebral surface. There are three surfaces: the superolateral, medial, and inferior, which are defined by three edges, the superior, lateral, and medial. Each hemisphere shows three poles, frontal, occipital, and temporal, and five lobes: frontal, parietal, occipital, temporal, and the insula (Figs. 1.1–1.4). The cerebral hemispheres are separated by the medial longitudinal fissure (or interhemispheric fissure).

The cerebrum presents four main sulci that are 100% uninterrupted. These are the sylvian fissure, the callosal, the parieto-occipital, and the collateral sulci. Moreover, two sulci, the central and the calcarine sulci are almost continuous.

Frontal lobe

The frontal lobe is the largest lobe of the brain (Figs. 1.1–1.6). ³ , ⁴ It is delimited posteriorly from the parietal lobe by the central sulcus, medially from the cingulate gyrus by the cingulate sulcus and inferiorly, from the temporal lobe by the Sylvian fissure. The frontal lobe can be divided into four parts, the lateral, polar, orbital or basal, and medial part. The most anterior part of the frontal lobe is also known as the anterior pole. ⁵

Figure 1.1  Four main lobes of the cerebrum.

Figure 1.2  The fifth lobe of the cerebrum, the insula (green).

Figure 1.3  Cerebral gyri.

Figure 1.4  Cerebral sulci.

Figure 1.5  Cerebral gyri and anatomical formations in the medial surface of the brain at midline.

Figure 1.6  Cerebral sulci in the medial surface of the brain at midline.

Sulci

The lateral surface of the frontal lobe presents three main sulci, the precentral sulcus, the superior, and the inferior frontal sulcus. The precentral sulcus starts from the medial surface of the hemisphere, at the superior edge, and continues at the lateral surface downwards and parallel to the central sulcus. It ends just above the Sylvian fissure. The superior frontal sulcus starts anteriorly and about in the middle of the precentral sulcus, traveling anteriorly and inferiorly. The inferior frontal sulcus runs parallel and inferiorly to the superior frontal sulcus.

The medial surface of the frontal lobe presents with the cingulate and the callosal sulcus, which separate the cingulate gyrus and the corpus callosum, respectively. The cingulate sulcus starts from the rostrum of corpus callosum and arcs posteriorly above the cingulate gyrus. At the end of the body of the corpus callosum, the cingulate sulcus arcs superiorly and ends at the edge of the hemisphere. The last part of the cingulate sulcus is called the marginal sulcus. At the level of the middle of the corpus callosum, the cingulate sulcus gives a ramus that runs superior, and it is called paracentral sulcus.

The basal surface presents the olfactory sulcus and the orbital sulcus. The latter is an H shaped sulcus that divides the orbital part of the frontal lobe into four orbital gyri.

Gyri

The lateral surface of the frontal lobe demonstrates four gyri, the precentral, the superior, middle, and inferior frontal gyrus. The precentral gyrus is located on the lateral surface between the central sulcus and the precentral sulcus, extending to the medial surface. The superior frontal gyrus can be located superior to the superior frontal sulcus. The middle frontal gyrus can be found between the superior frontal sulcus and the inferior frontal sulcus. The inferior frontal gyrus is located between the inferior frontal sulcus and the Sylvian fissure. The horizontal and the ascending rami of the Sylvian fissure divide the inferior frontal gyrus into the pars orbitalis, pars triangularis, and pars opercularis.

The medial part of the frontal lobe can be found superior to the cingulate gyrus. The latter runs parallel to the superior frontal gyrus, and it is located between the callosal and cingulate sulcus. The medial surface presents also the paracentral lobule, which is formed from the precentral and postcentral gyrus. It is delimited anteriorly by the paracentral sulcus, posteriorly by the marginal sulcus, inferiorly by the cingulate sulcus, and superiorly by the edge of the cerebral hemisphere.

The basal surface of the frontal lobe demonstrates the rectus gyrus and the orbital gyri. The former is a sagittal gyrus located medially to the olfactory sulcus. The orbital gyri are delimited by the orbital sulcus, and they comprise four gyri, the anterior, posterior, lateral, and medial orbital gyrus.

Functions in frontal lobe

The cortex of the precentral gyrus is the primary motor cortex, which is responsible for executing movement but not designing the movement. ⁶ , ⁷ Different parts of the body are represented in different areas in the primary motor cortex. This specific distribution is also known as the homunculus of Penfield. The leg area is medially and close to the middle, the head and face are lateral near the Sylvian fissure, and between the two, the hand and arm motor area are found. The centers for micturition and defecation are represented at the paracentral lobule. The cortex of the anterior part of the precentral sulcus, along with the cortex of the posterior part of the superior, middle, and inferior frontal gyrus, makes the premotor cortex. The latter is responsible for storing the movement blueprint and participating in crude movements. It may play a role in planning movement, understanding actions of others, or even direct control of behavior. The exact role is still under investigation.

Just anterior to the paracentral lobule, at the superior edge and on the medial surface of the cerebral hemisphere, lies the supplementary motor area (SMA). ⁸ The exact role of the SMA has not been proven, but it is highly related to planning of movement sequences, postural stability during stances, and bimanual coordination.

The cortex of the posterior part of the middle frontal gyrus represents the frontal eye field. Stimulation of this area produces conjugated movement of the eyes toward the contralateral side, whereas a destructive lesion of the area will produce conjugated movement of the eyes toward the ipsilateral side.

The cortex of the pars triangularis and the pars opercularis is traditionally considered the motor center of speech. It is also known as the area of Broca, in memory of Paul Broca who first described the area and the function in 1861. The cortex anterior to the precentral gyrus and the premotor cortex is called prefrontal cortex, which is responsible for the personality and the depth of emotions.

Parietal lobe

The parietal lobe is defined by the central sulcus, the Sylvian fissure, the parieto-occipital, and the interhemispheric fissure (Figs. 1.1–1.6). ⁹ , ¹⁰

Sulci

The lateral surface of the parietal lobe presents with two main sulci, the postcentral and the intraparietal sulcus. The postcentral sulcus can be found behind and parallel to the central sulcus, whereas the intraparietal sulcus starts around the middle of the postcentral sulcus and travels in the anteroposterior axis up to the transverse occipital sulcus. In the medial surface of the hemisphere, the parietal lobe presents the subparietal sulcus, which is a continuation of the cingulate sulcus.

Gyri

The postcentral gyrus can be found between the central and the postcentral sulcus. The superior parietal lobule is delimited by the postcentral sulcus, the posterior edge of the hemisphere, the superior edge of the hemisphere, and the intraparietal sulcus. The inferior parietal lobule can be found between the intraparietal sulcus, the temporal lobe, the postcentral sulcus, and the occipital lobe. The inferior parietal lobule comprises the supramarginal and angular gyrus. The former extends around the posterior end of the Sylvian fissure, and the latter extends around the posterior end of the superior temporal sulcus. The medial surface of the parietal lobe presents with the precuneus, which lies between the superior edge of the hemisphere, the subparietal sulcus, the marginal branch of the cingulate sulcus, and the parieto-occipital fissure.

Functions in parietal lobe

The cortex of the postcentral gyrus and the posterior part of the paracentral lobule is the primary somatosensory cortex, and consequently the general sensations of touch, pressure, pain, temperature, and proprioception. ¹¹ , ¹² The areas of the body are represented in the sensory cortex in a specific distribution, called the somatosensory homunculus of Penfield, which is the equivalent of the homunculus of Penfield in the motor cortex. The areas of the body with the most important functions (face, lips, tongue, thumb) are represented with larger areas in the sensory cortex. The cortex of the superior parietal lobule is involved in daydreaming, introspection, aspects of attention, and visuospatial perception, including the representation and manipulation of objects. The dominant inferior parietal lobule is involved in reading, writing, and arithmetic. More analytically, the supramarginal gyrus includes the sensory center of the speech, the center of understanding verbal speech. This center is also known as Wernicke's area, discovered and named by Wernicke in 1874. In the angular gyrus, the visual center of speech can be found, which is responsible for understanding written speech. Wernicke's area receives afferent fibers from the auditory cortex in the temporal lobe, the visual cortex in the occipital lobe, and sends efferent fibers in the motor speech area (Broca's area).

Temporal lobe

The temporal lobe lies under the Sylvian fissure in the middle cranial fossa. It is located anterior to the occipital lobe, posterior and inferior to the frontal lobe (Figs. 1.1–1.7). The posterior limit is an imaginary line drawn from the preoccipital notch to the Sylvian fissure. ¹³–¹⁵ The temporal lobe anatomy is one of the most difficult anatomies of the brain and exceeds the scope of the book. Therefore, a cruder anatomy of the temporal lobe will be presented.

Sulci and gyri

At the superior surface of the temporal lobe, there are 3-4 transverse sulci, which create two transverse gyri (transverse gyri of Heschl). The cortex of these gyri is the auditory cortex. The temporal lobe is involved in visual memories, long-term memory, processing sensory input (either auditory or visual), language recognition, and music recognition.

The lateral surface of the temporal lobe presents with two sulci and three gyri. The superior temporal gyrus lies between the Sylvian fissure and the superior temporal sulcus. The middle temporal gyrus is found between the superior temporal sulcus and the inferior temporal sulcus. The posterior part of the middle temporal gyrus continues as the angular gyrus. The inferior temporal gyrus is found between the inferior temporal sulcus and the lateral occipitotemporal sulcus, and it is connected posteriorly with the inferior occipital gyrus.

The medial surface of the temporal lobe includes the fusiform gyrus (also known as lateral occipitotemporal gyrus), which is delineated by the lateral occipitotemporal sulcus and the collateral sulcus. Medially to the collateral sulcus, the hippocampal gyrus (also known as parahippocampal gyrus) can be found (Fig. 1.7). The parahippocampal gyrus starts posteriorly and inferiorly of the splenium of the corpus callosum as a continuation of the isthmus of the cingulate gyrus and ends anteriorly at the uncus of the hippocampus. The hippocampal formation comprises the dentate gyrus, hippocampus proper, fimbria, subiculum, and entorhinal cortex. The parahippocampal gyrus along with the lingual gyrus of the occipital lobe make the medial occipitotemporal gyrus. The hippocampal sulcus (also known as hippocampal fissure) separates the dentate gyrus from the subiculum.

Figure 1.7  Hippocampal formation. The image on the left is a normal T1WI sequence of an MRI. The red and yellow squares show the right and the left hippocampal formation, respectively. The image on the right represents the yellow square (left hippocampal formation). CA, cornu ammonis (=hippocampus).

Occipital lobe

The occipital lobe lies posteriorly to the parietal and temporal lobe (Figs. 1.1–1.6). Inferiorly, it is separated from the cerebellum by the tentorium cerebelli. The most posterior part of the occipital lobe is called occipital pole. ¹⁶ , ¹⁷

Sulci

The sulci include the transverse occipital sulcus, which is oriented from superior and posterior toward anterior and inferior; the lateral occipital sulcus, which has sagittal orientation and ends just anterior to the occipital pole; and the intraoccipital sulcus, which is an extension of the intraparietal sulcus of the parietal lobe. The medial surface of the occipital lobe presents the calcarine sulcus (also known as calcarine fissure). It extends from the parieto-occipital sulcus to the occipital pole.

Gyri

The lateral surface of the occipital lobe has two gyri, the superior and inferior occipital gyrus separated by the lateral occipital sulcus. Occasionally the occipital lobe is divided into three gyri, superior, middle, and inferior separated by the lateral occipital sulcus and an extension of the transverse occipital sulcus.

The medial surface presents the lingual gyrus and a formation called cuneus. The latter has a triangular shape with the top turned at the isthmus of the cingulate gyrus. It is located between the calcarine sulcus and the parieto-occipital sulcus. The lingual gyrus lies between the calcarine and the collateral sulcus.

Functions in occipital lobe

In the upper and lower banks of the calcarine sulcus is the primary visual cortex. Nerve fibers come from the temporal field of the ipsilateral retina and from the nasal field of the contralateral retina end in the visual cortex. The fibers of the superior and inferior quadrants of the retina can be found in the visual cortex above and below the calcarine fissure, respectively.

Central lobe or insula or Island of Reil

The insular lobe lies underneath the frontal, parietal, and temporal lobe, deep in the Sylvian fissure. The cortical structures that cover the insular cortex are called the operculum, and it is divided into three portions, the frontal, the parietal, and the temporal operculum. The frontal operculum comprises the pars triangularis, pars opercularis, and the inferior portion of the precentral gyrus. The parietal operculum lies between the inferior portion of the postcentral gyrus and the posterior rami of the Sylvian fissure. The frontal and the parietal operculum are grouped together, and they are known as the frontoparietal operculum. The temporal operculum comprises the superior temporal gyrus and the transverse temporal (Heschl's) gyri. ¹⁸ , ¹⁹

The insular lobe has a triangular shape with its base superiorly and the vertex toward inferiorly and laterally. The circular sulcus can be found around the insular lobe, which separates the insula from the operculum. There is also a central sulcus that divides the insula into anterior and posterior. The anterior part includes short gyri (the anterior, middle, and posterior short gyrus), which fan out from the vertex. The posterior part consists of the long gyri (the anterior and posterior long gyrus). The most anteroinferior part of the insular cortical surface is the limen of insula. It forms the lateral limit between the insular cortex and the anterior perforated substance, and it is the transition point to the olfactory cortex. The limen of insula is the point where the middle cerebral artery typically bifurcates/trifurcates.

The insula has connections to the neocortex, basal ganglia, thalamus, limbic system, and olfactory cortex. Its function has been linked to visceromotor and viscerosensory functions, desires, cravings, and addiction. ¹⁹ , ²⁰

Cerebral cortex and layers

The surface of the cerebral cortex is about 200,000–240,000mm², its weight is about 450g, and the thickness varies from 1.5 to 4.5mm. It consists of nerve cells, glial cells, nerve fibers, and blood vessels. The number of nerve cells in the cerebral cortex of an adult is about 10 billion. The cerebral cortex can be divided into the neocortex, which covers 90% of the brain, and the allocortex. The cerebral neocortex is organized into six layers, which include the neurons and the nerve fibers (i.e., the axons of the neurons).

Basal ganglia and diencephalon

Basal ganglia

The basal ganglia are a complex of gray matter within the white matter, deep in the base of the cerebral hemispheres (Fig. 1.8). They are located below the floor of the lateral ventricles, medial to the insular lobe, and above the midbrain. They are a group of subcortical nuclei, and they consist of the striatum [dorsal striatum (caudate nucleus and putamen), ventral striatum (nucleus accumbens and olfactory tubercle)], the globus pallidus (internal and external), the claustrum, ventral pallidum, substantia nigra, and the subthalamic nucleus. The caudate nucleus and the putamen can be grouped together and called neostriatum, whereas the globus pallidus is also known as paleostriatum. The putamen and the globus pallidus can also be grouped together and are known as lentiform nucleus. ²¹–²⁶

The caudate nucleus has a c-shaped formation, with the open part of the c looking anteriorly and inferiorly. ²⁷ Its orientation is sagittal along the outer wall of the lateral ventricle, lateral to the thalamus. Its length is about 6–7cm, and its width varies but becomes thinner from anterior to posterior. It has a head, body, and tail. The head of the caudate nucleus is the inferior and lateral wall of the frontal horn of the lateral ventricle. Lateral and dorsal, it is separated from the lentiform nucleus by the anterior limb of the internal capsule, whereas ventrally it is connected to the lentiform nucleus. Inferiorly, the head is connected to the anterior perforated substance. The body of the caudate nucleus is the inferior wall of the body of the lateral ventricle. It is separated medially from the thalamus with the stria terminalis and the thalamostriate vein. Laterally, it communicates with the corona radiata and inferiorly with the internal capsule. The tail of the caudate nucleus is part of the superior wall of the temporal horn of the lateral ventricle. Anteriorly, it is connected to the amygdaloid nucleus and dorsally it communicates with the lentiform nucleus.

Figure 1.8  Right side basal ganglia in 3D space.

The lentiform nucleus is a triangular-shaped gray matter with the base situated lateral, when it is seen in an axial and coronal cut, and a biconvex lens in a sagittal cut. ²⁸ Laterally, it is separated from the claustrum by the external capsule. Medially, the anterior limb of the internal capsule separates it from the head of the caudate nucleus, and posterior limb separates it from the thalamus. Inferiorly and anteriorly, it is connected to the head of the caudate nucleus, and posteriorly it is separated from the superior wall of the temporal horn of the lateral ventricle with the tail of the caudate nucleus. The lentiform nucleus has two medullary laminae, which divide it into three parts. The lateral medullary lamina divides the lentiform nucleus into the putamen, which lies lateral, and the globus pallidus, which lies medially. The medial medullary lamina divides the globus pallidus into internal globus pallidus (GPi) and external globus pallidus (GPe).

The claustrum is a thin gray matter located between the insula and the putamen. It is separated from the insula by the extreme capsule and from the putamen by the external capsule. ²⁹ , ³⁰ The amygdaloid nucleus (also known as amygdala) is an almond-shaped nucleus, which lies at the anterior and superior end of the temporal horn of the lateral ventricle, where it merges with the tail of the caudate nucleus. Superiorly, the amygdaloid nucleus is in contact with the cortex of the uncus of the hippocampus. Anteriorly, it is in contact with the limen of insula. Superiorly and medially, it is in contact with the anterior perforated substance, and posteriorly with the tail of the caudate nucleus. Histologically, the amygdaloid nucleus is actually a complex of nuclei grouped into two groups. The medial group consists of the cortical, medial, and central amygdaloid nucleus. The lateral group consists of the lateral, basal, and accessory basal nucleus.

The nucleus accumbens is located in the basal forebrain rostral to the preoptic area of the hypothalamus. ³¹ , ³² Posteriorly, it is in contact with the posterior border of the anterior commissure. The anterior limit is found where the rostral limit of the internal capsule separates the caudate nucleus from the putamen. Medially, it is limited by the sagittal plane in the inferior border of the lateral ventricle. Laterally, it is limited by an imaginary line passing by the rostral edge of the internal capsule. The dorsal limit is the horizontal plane passing under the head of the caudate nucleus to the inferior limit of the internal capsule. The ventral limit is the external capsule, the diagonal band of Broca, and the anterior hypothalamic nucleus.

The olfactory tubercle is a round bulge in the basal forebrain and it varies in location and size between humans. It is located anterior to the optic chiasm and posterior to the olfactory peduncle.

The substantia nigra is located in the midbrain, posterior to the crus cerebri fibers of the cerebral peduncle. ³³ , ³⁴ It can be divided into two regions with different function and morphology. The substantia nigra pars compact (SNpc) and the substantia nigra pars reticulata. The former has dopaminergic projections to the striatum, the putamen, and the caudate nucleus. The latter has GABAergic projections conveying information to the thalamus and superior colliculus.

The subthalamic nucleus is a small lens-shaped nucleus that is located ventral to the thalamus, dorsal to the substantia nigra, and medial to the internal capsule. ³⁵

Diencephalon

The diencephalon consists of the thalamus, the hypothalamus (including the posterior pituitary), the subthalamus, and the epithalamus. The latter includes the anterior and posterior paraventricular nuclei, medial and lateral habenular nuclei, stria medullaris thalami, posterior commissure, and the pineal body.

Thalamus

The thalami are two oval-shaped complexes superior to the midbrain, which form the lateral wall of the third ventricle. The dimension of the thalamus is about 4cm in length, 2cm in width, and 2–2.5cm in height. The thalamus is angled 30 degrees to the midline. The two thalami are connected by interthalamic adhesion (also known as intermediate mass or middle commissure). It has two edges (anterior, posterior) and four surfaces (superior, inferior, lateral, and medial). The anterior edge of the thalamus, along with the respective anterior pillar of fornix, forms the foramen of Monro. The posterior edge is also called the pulvinar, and it is related to the lateral and medial geniculate body. The superior surface forms the floor of the body of the lateral ventricle, whereas the inferior surface is related anteriorly to the subthalamus and hypothalamus, and posteriorly to the tegmentum of the brain. The medial surface is the lateral wall of the third ventricle and has the mass intermediate. The lateral surface is separated from the lentiform nucleus by the posterior limb of the internal capsule. Each thalamus has an external and internal lamina. The former covers the lateral surface, and the latter divides the thalamic nuclei into anterior, medial, and lateral groups. ³⁶ The thalamic nuclei are anterior, medial, lateral, nuclei of the pulvinar, medial and lateral geniculate bodies, reticular nuclei, paraventricular nuclei (also known as nuclei mediani or midline thalamic nuclei), and the intralaminar nuclei.

Hypothalamus

The hypothalamus is a collection of nuclei located centrally in the brain. It constitutes the lateral walls and the floor of the third ventricle. The floor of the third ventricle is the main hypothalamus, which comprises the mammillary bodies, the tuber cinereum, the choana, the pituitary, part of the optic chiasm, and the lamina terminalis. The hypothalamus is delimited by the lamina terminalis, pituitary gland, mammillary bodies, and superior hypothalamic sulcus. It is divided into three zones surrounding the mammillary bodies and the third ventricle. The hypothalamus has connections to the brainstem, the cerebral cortex, the hippocampus, the amygdala, the thalamus, the pituitary, and the retina. The hypothalamus has four groups of nuclei, the preoptic region, the supraoptic nuclei, the tuberal region, and the mammillary region. ³⁷ , ³⁸

The hypothalamus is involved in the functions of the sympathetic and the parasympathetic nervous system. It is also involved in the regulation of body temperature, water homeostasis, metabolism of carbohydrates, appetite, sleep and alertness, and sexual behavior. It also affects behavior and emotions through its connections to the limbic system. ³⁷ , ³⁹

Brainstem

Midbrain

The midbrain connects the diencephalon with the pons and the cerebellum, and it is approximately 1.5–2cm in length. ⁴⁰ , ⁴¹ It has a dorsal and a ventral surface, and two lateral surfaces. At the dorsal surface, there is the quadrigeminal plate (also known as tectal plate or tectum), which consists of the superior and inferior colliculi. The quadrigeminal plate extends from the pineal gland to the superior medullary velum. At the lateral surfaces of the colliculi, there is the brachium of the colliculi. The superior brachium connects the superior colliculi with the lateral geniculate body. It is approximately 2.5cm, and it travels transversely and laterally, inferior to the pulvinar of the thalamus. The inferior brachium is smaller in length (0.5–1cm), and it travels superiorly and laterally, connecting the inferior colliculi with the medial geniculate body. The superior colliculi are divided by the medial longitudinal fissure, which broadens inferiorly and forms the frenulum veli. The ventral surface of the midbrain comprises the cerebral peduncles and between them the posterior perforated substance.

In the middle of the midbrain, there is the aqueduct of Silvius. It is a narrow pipeline of about 1.5cm in length and width of about 1–2mm traveling the midbrain. It connects the third ventricle to the fourth ventricle. It lies underneath the quadrigeminal plate and the superior medullary velum, and it is surrounded by a thin layer of neurons that consists of gray mater.

Pons

The pons lies between the cerebral peduncles (cranially), the medulla oblongata (caudally), and the cerebellar (laterally). ⁹ , ⁴² , ⁴³ The limits are the superior pontine sulcus and the inferior pontine sulcus, and laterally a line from the exit of the trigeminal nerve to the exit of the facial nerve. The ventral surface of the pons is found in the cranial part of the clivus of the occipital bone, and it is curved at the sagittal and axial levels. The dorsal surface of the pons is triangular, it is covered by the cerebellum, and it is part of the rhomboid fossa.

Medulla oblongata

The medulla oblongata has the shape of a cone that connects cranially to the pons, and caudally to the spinal cord. It has a ventral and a dorsal surface, as well as two lateral surfaces. ⁴⁴–⁴⁶ The ventral surface has the anterior-median fissure, the pyramid, and the anterolateral sulci. The lateral surface comprises the olive, the fossa supraolivar, the posterior and anterior olivary sulcus. The dorsal surface comprises the posterior median sulcus, the inferior cerebellar peduncles, the gracile fasciculus, cuneate fasciculus, gracile tubercle, and cuneate tubercle, and lateral to each cuneate nucleus is the trigeminal tubercle. Caudal to the trigeminal tubercle is the lateral funiculus of the medulla oblongata.

Cerebellum

The cerebellum lies in the posterior fossa, behind the pons and the medulla oblongata, separated from them with the fourth ventricle. It has a superior and inferior surface, with the primary fissure and the secondary fissure, respectively. ⁴⁷ There is also a horizontal fissure (a.k.a. fissure of Vick d’Azyr).

The cerebellum is divided into the vermis (superior and inferior vermis) and the hemispheres. The superior vermis consists of the lingula, the central lobe, the culmen, and the declive, whereas the inferior vermis consists of the folium, the tuber, the pyramid, and the uvula.

The cerebellar hemispheres have a superior and an inferior surface. On the superior surface, is the ala, the quadrangular lobule, the lobulus simplex, and superior semilunar lobule. The inferior surface consists of the tonsil, the biventral lobule, the inferior semilunar lobule, and the flocculus.

There are three peduncles; the superior cerebellar peduncles connect the cerebellum with the midbrain, the middle cerebellar peduncles connect the pons to the cerebellum, and the inferior cerebellar peduncles connect the medulla oblongata to the cerebellum.

There are four pairs of nuclei in the cerebellum, the dentate nucleus (lateral), the globose, the emboliform, and the fastigial (medial).

White matter—fiber tracts

The space between the gray matter and the subcortical nuclei of the brain is white matter, that is, the fiber tracts. These are categorized into three types, the association fibers that connect cortical areas of the same hemisphere, the commissural fibers that connect respective areas of the two hemispheres, and the projection fibers that connect cortical to subcortical areas. The white matter tracts will be analyzed further in Chapter 3.

Association fibers

The association fibers are axons that connect cortical areas of the same cerebral hemisphere. They are divided into two types, the short association fibers and the long association fibers.

Short association fibers

The short association fibers connect adjacent gyri. They are subcategorized into cortical that travels in the deeper layers of the cortex, and subcortical (also known as arcuate or U fibers) that lies immediately underneath the gray matter of the cortex. The U fibers connect together adjacent gyri. ⁴⁸

Long association fibers

The long association fibers connect more distant parts of the same cerebral hemisphere, and they are grouped into bundles (fasciculus). These include the following:

- The uncinate fasciculus (UF)

The uncinate fasciculus is a hook-shaped white matter bundle that connects the limbic system of the temporal lobe to the orbitofrontal cortex. ⁴⁹ More specifically, it starts at the anterior temporal lobe and amygdala and travels in the anterior temporal lobe curving upward behind the external capsule (underneath the insular cortex) ending at the orbital gyri and part of the inferior frontal gyrus.

- The cingulum

This lies in the cingulate gyrus and connects the entorhinal cortex to the limbic system. ⁵⁰ It forms the white matter of the cingulate gyrus, from the subcallosal gyrus to the parahippocampal gyrus and uncus of the temporal lobe.

- The superior longitudinal fasciculus (SLF)

It is composed of three different components SLF I, SLF II, and SLF III. ⁵¹–⁵⁴ It is present in both hemispheres lateral to the centrum semiovale and connects the frontal, occipital, parietal, and temporal lobes. It courses from the frontal lobe, through the operculum, to the posterior end of the Sylvian fissure where a part of it radiates to the occipital lobe and another part turns downward traveling forward around the putamen, up to the anterior temporal lobe.

- The inferior longitudinal fasciculus (ILF)

It connects the occipital lobe to the temporal lobe and it is the white matter bundle of the ventral visual stream. ⁵⁵ It connects the ventral surface of the anterior temporal lobe, traveling along the lateral and inferior wall of the lateral ventricle, to the occipital lobe.

- The vertical occipital fasciculus (VOF)

The vertical occipital fasciculus runs vertically and connects areas of the occipital lobe between themselves and to the inferior parietal lobule. ⁵⁶

- The inferior occipitofrontal fasciculus

The inferior occipitofrontal fasciculus travels from the frontal lobe, along the lateral border of the caudate nucleus, at the external capsule, and along the roof of the temporal horn of the lateral ventricle to the occipital lobe. ⁵⁷ The superior occipitofrontal fasciculus does not exist in human brains.

- The arcuate fasciculus

The arcuate fasciculus is a bundle of white matter that connects Broca's and Wernicke's area, that is, the inferior frontal lobe and the temporal lobe. It runs parallel to the SLF, and many neuroscientists refer to them interchangeably. ⁵⁸ The SLF and AF can be distinguished by their function and the endpoint. The AF terminates at the Broca's area and its function is the processing of complex syntax, whereas the SLF ends in the premotor cortex and its function is acoustic-motor mapping. ⁵⁹ , ⁶⁰

Commissural fibers

The commissural fibers are transverse fibers that connect the two hemispheres of the brain.

- Corpus callosum (CC)

The corpus callosum is the largest commissural tract and it consists of about 200–300 million axons. It connects the two hemispheres, and it is essential for their communication. It is about 10cm long, and it can be found on the floor of the longitudinal fissure of the brain. It has four main parts, the rostrum, the genu, the trunk (or body), and the splenium, whereas a narrowed part between the body and the splenium is known as the isthmus. The fibers of the body and the splenium form the tapetum of the corpus callosum, which is the roof of each lateral ventricle. It is separated from the hemispheres by the callosal sulcus, which separates the CC from the cingulate gyrus. ⁶¹ , ⁶²

- Anterior commissure (AC)

The anterior commissure connects the two temporal lobes of the cerebral hemispheres. ⁶³ It is situated in the midline anterior to the columns of the fornix and plays a key role in pain sensation, sense of smell, and chemoreception. It also interconnects the amygdala and the temporal lobes, playing a role in memory, emotion, speech, and hearing.

- Posterior commissure

The posterior commissure is a white matter bundle located dorsally of the rostral end of the cerebral aqueduct, underneath the base of the pineal gland. ⁶⁴ It is involved in the bilateral pupillary light reflex.

Projection fibers

The projection fibers are white matter bundles that connect the brain with lower parts of the brain and with the spinal cord. They are categorized into efferent fibers that convey the information away from the brain and afferent fibers that convey the information toward the brain.

The most important efferent fibers are (1) the motor tract and (2) the corticopontine fibers.

The most important afferent fibers are (1) sensory tracts, (2) medial lemniscus, (3) the fibers of the superior cerebellar peduncle in the red nucleus and thalamus, (4) fibers arising from thalamus to the cortex, and (5) optic and acoustic fibers.

Neural tracts—pathways

Motor tracts

Pyramidal tract

The pyramidal tract comprises the corticobulbar and the corticospinal tract, and it is responsible for voluntary movements. It is formed by upper motor neurons, and it is a system of efferent nerve fibers. It carries signals from the cerebral cortex to the brainstem (corticobulbar) or the spinal cord (corticospinal). ⁶⁵ The nerve fibers of the corticospinal tract originate from the pyramidal cells in layer V of the cortex. About 1/3 of the fibers originate from the primary motor cortex (Brodmann area 4), about 1/3 originate from the premotor cortex (Brodmann area 6), and the rest comes from the parietal lobe (Brodmann areas 3, 1, 2) as well as the cingulate gyrus. Different parts of the body are represented in different areas in the motor cortex. The area that controls the face lies caudally in the motor cortex, whereas the area that controls the leg lies cranially in the motor cortex. Approximately 60% of the fibers are myelinated and the rest are unmyelinated. The nerve fibers travel through the corona radiata, the internal capsule, the midbrain, the pons, and the medulla oblongata. They follow a somatotopic distribution in the internal capsule, and thus the fibers that represent the body from head to toe are distributed to the genu of the internal capsule toward the posterior limb, respectively. In the midbrain, the fibers are located in the cerebral peduncles, and they are distributed from lateral to medial. The fibers coming from the parietal lobe are located lateral, and the fibers from the legs, trunk, arms, and head are found going toward medially. In the pons, the fibers from head, arms, and legs are distributed from cranially to caudally, respectively. In the medulla oblongata, the pyramidal tracts are forming two prominences which are called the medulla oblongata pyramids. Below these prominences, at the transition of the medulla oblongata to the spinal cord, the majority of the axons are decussated, which is known as the pyramid decussation. About 70%–90% of the crossed fibers travel in the contralateral half of the spinal cord where they form the lateral corticospinal tract. In this tract, the fibers for the arms travel medially and the fibers for the legs laterally. About 50% of the fibers of the lateral corticospinal tract end in the cervical region, 20% in the thoracic region, and 30% to the lumbosacral region, The rest of the uncrossed fibers in the pyramids form the anterior corticospinal tract that travels in the anterior white column of the spinal cord and eventually crosses to the contralateral side through the anterior white commissure. The fibers from the corticospinal tract end at the neurons in the anterior horns of the spinal cord, where they connect with lower motor neurons and end in the muscles. The corticobulbar tract follows the same course as the corticospinal tract, but it ends at its synapse with the nuclei of the cranial nerves.

Extrapyramidal system

The extrapyramidal system is part of the motor system, and it is responsible for involuntary actions. ⁶⁶ It is a constellation of cortical and subcortical centers and tracts that influence the function of the skeletal muscles. The extrapyramidal system contributes to the realization of a movement by causing the competitors of the movement muscles to relax. It also contributes to the static and dynamic balance of the body. It modulates the involuntary movements that accompany several voluntary movements, such as gestures or hand movements during speech. It controls the involuntary movements of the arms during walking, or other habitual or acquired movements such as swimming or dancing. It also regulates the involuntary movements during the flight or fight response against visual or auditory stimuli. The cortical centers involved in the extrapyramidal system are the premotor cortex (Brodmann area 6), the cortical areas of the frontal lobe (Brodmann areas 8, 9, and 24), the cortical areas of the occipital lobe (Brodmann area 19), and the cortical areas of the parietal and temporal lobe.

The subcortical centers that are involved in the system are the globus pallidus, the striatum, the red nucleus, the substantia nigra, the subthalamic nucleus, the cerebellum, the anteroventral nucleus of the thalamus, the vestibular nuclei, the olivary nuclei, and the reticular formation.

Sensory tracts

The somatosensory pathway comprises three neurons, the primary, the secondary, and the tertiary neuron. These are found in the dorsal root ganglion, the spinal cord, and the thalamus, and they end in the postcentral gyrus in the parietal lobe. The postcentral gyrus is the primary somatosensory area, and it shows a specific distribution similar to that of the motor cortex. With the somatosensory pathway, tactile and other somatosensory stimuli that activate receptors on the skin, muscles, tendons, and joints are carried from the periphery to the brain, and thus it is also known as the ascending pathway. The two major pathways that convey stimuli to the brain are the medial lemniscus (a.k.a. dorsal column system) and the spinothalamic tract. ⁶⁷ , ⁶⁸ The medial lemniscus is primarily responsible for touch, pressure, vibration, and proprioception, whereas the spinothalamic tract is responsible for pain and temperature sensations. Both of the tracts decussate but at different levels. The dorsal system decussates at the brainstem, and the spinothalamic pathway in the spinal cord, at the same level where the information first entered the spinal cord. These pathways carry information from the body, but not the head, which is carried by the trigeminal pathway. In the latter, the spinal trigeminal nucleus receives sensory stimuli of pain and temperature, and the mesencephalic nucleus in the midbrain receives stimuli such as touch, pressure, vibration, and proprioception. There are other sensory pathways with which the brain understands the environment. These include the gustation pathway (taste), the vestibular pathway (balance), the smell, the auditory pathway (hearing), the optic pathway (vision), and the autonomic pathway (vasoconstriction and perspiration).

Vasculature and blood supply of the brain

Arteries

The brain is vascularized from four major arteries, that is, the two internal carotid arteries and the two vertebral arteries. These arteries are found in the subarachnoid space and have several branches. Their anastomosis creates the circle of Willis. ⁶⁹ , ⁷⁰ The internal carotid artery enters the cranial vault through the carotid canal which is located in the petrous bone of the temporal bone. It crosses the cavernous sinus and enters the subarachnoid space and presents several important branches, the posterior communicating artery (PCOM) which anastomoses the internal carotid artery with the posterior cerebral artery, and the anterior choroidal artery (AChA), which travels posteriorly along the optic tract and enters the temporal horn of the lateral ventricle. The AChA supplies the optic tract, the optic radiation, the hippocampus, the tail of the caudate nucleus, the amygdala, part of the thalamus, and part of the globus pallidus. The internal carotid artery ends at its bifurcation into the anterior cerebral artery (ACA) and the middle cerebral artery (MCA). The former travels along the longitudinal fissure of the brain, around the