Topics in Behavioral Neurology and Neuropsychology: With Key References
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Topics in Behavioral Neurology and Neuropsychology - Daniel B. Hier
sections.
1
Cerebral Organization
Publisher Summary
This chapter discusses the classification and different aspects of cerebral organization. A large number of disorders of higher cortical function are now recognized, but no completely satisfactory schema exists for categorizing them. Conduction aphasia may follow injury to the left insula. The term cerebral dominance reflects the observation that language functions are usually lateralized to the left hemisphere and visual-spatial functions are usually lateralized to the right hemisphere. Dichotic listening studies suggest that speech is less firmly lateralized to the left hemisphere in left-handers than in right-handers. Left-handedness appears to predict the anomalous patterns of cerebral organization. The transfer of language from the left to right hemisphere has a number of consequences. A variety of behavioral syndromes may occur after the interruption of the corpus callosum, which is the most important commissure connecting the cerebral hemispheres. The corpus callosum is occasionally sectioned to control intractable epilepsy. Partial sectioning may occur after cerebral infarction or when tumors are surgically removed from the vicinity of the corpus callosum.
CLASSIFICATION OF DISORDERS OF HIGHER CORTICAL FUNCTION
A large number of disorders of higher cortical function are now recognized, but no completely satisfactory schema exists for categorizing them. Traditionally, disorders of higher cortical function have been grouped according to major behavioral disturbance:
Aphasias: disorders of language
Apraxias: disorders of skilled movement
Agnosias: nonperceptual disorders of recognition
Alexias: disorders of reading
Agraphias: disorders of writing
Acalculias: disorders of calculating
Dementias: global disorders of intellect
Amnesias: disorders of memory
Unfortunately this schema is not complete, and many disorders are difficult to classify (e.g., right-left confusion, confabulation). Disorders may also be grouped by the main modality affected (e.g., visual, auditory, or somesthetic), by whether they are motor (executive) or sensory (receptive), and by whether they are developmental or acquired. Unfortunately, none of these schemas permits easy classification of all disorders. Classification of disorders by major site of involvement (e.g., frontal, parietal) is useful (see below), but for many disorders (e.g., amusia, anosognosia) the exact site of the injury responsible for the disorder is uncertain.
Within both hemispheres, certain general patterns of intrahemispheric organization exist. Brain mass anterior to the central sulcus (rolandic sulcus) subserves motor (executive) functions, whereas brain mass posterior to the central sulcus subserves sensory (receptive) functions. The frontal lobe is involved not only in the execution of motor acts but in generating much of the motivation that drives these acts. A variety of higher cortical deficits may follow frontal lobe injury (Table 1.1).
Table 1.1
Frontal Lobe Disorders
Parietal cortex subserves tactile sensation (somatesthesis). The inferior parietal lobule (angular gyrus region) serves to integrate sensory information (thereby permitting visual, auditory, and tactile cross-modal associations). The left temporal-parietal-occipital junction, unlike the homologous area in the right hemisphere, must also integrate linguistic with sensory information. Hence, damage to this critical junction on the left produces a unique set of deficits that are both quasi-linguistic and quasi-perceptual (right-left confusion, alexia, agraphia, finger agnosia, and dyscalculia). Spatial and quasi-spatial mapping of sensory input occurs in both the left and right parietal lobes; however, the right parietal lobe appears more efficient for many of these operations. Deficits associated with parietal lobe injury are summarized in Table 1.2.
Table 1.2
Parietal Lobe Disorders
The temporal lobes have prominent olfactory and auditory functions and, because of their proximity to the underlying limbic system, have important modulating effects on emotion. The dominant left temporal lobe is the site of much of the primary language cortex within the brain. Deficits associated with temporal-lobe injury are shown in Table 1.3, and visual disturbances that follow injury to the occipital lobes are listed in Table 1.4.
Table 1.3
Temporal Lobe Disorders
Table 1.4
Temporal Lobe Disorders
The role of the insula remains largely a mystery. Conduction aphasia may follow injury to the left insula. Deep structures (especially the thalamus) subserve alerting functions for both hemispheres and act as a conduit for cortex-directed signals arising from the brain stem reticular-activating system. The thalamus also plays an important role in memory functions. The limbic system, which lies between the deep basal ganglionic nuclei and the surface cerebral cortex, is involved in memory, emotion, and possibly motivation. The pattern of deficits depends on the laterality of the brain injury. Memory deficits depend on the side of damage; left temporal lesions produce greater verbal memory deficits, and right temporal lesions produce greater nonverbal (visual-spatial) memory deficits. Similarly, emotional reactions also depend on the hemisphere damaged. Left-hemisphere damage is more likely to elicit depression or catastrophic reactions, while right-hemisphere damage tends to produce anosognosia (indifference reactions) and affective agnosia.
Mesulam (1981) has suggested that the two cerebral hemispheres may use different but complementary organizational schemes. Higher cortical functions appear to be localized to specific brain areas in the left hemisphere (e.g., Broca’s, Wernicke’s). In contrast, the right hemisphere appears to be organized by a series of overlapping networks (e.g., one for attention, one for motivation). The size of the various cortical areas devoted to higher cortical functions probably varies among individuals. For example, important differences may exist in the size of language zone. The work of Ojemann (1979) suggests considerable variability among individuals in intrahemispheric organization of higher cortical functions. Sex, handedness, and various factors (e.g., genetic, experiential) may influence the precise site and size of brain areas subserving higher cortical functions.
References
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McGlone, J, Davidson, W. The relationship between cerebral speech laterality and spatial ability with special reference to sex and hand preference. Neuropsychologia. 1973; 11:105–113.
McGlone, J, Kertesz, A. Sex differences in cerebral processing of visuospatial tasks. Cortex. 1973; 9:313–320.
Mesulam, M-M. A cortical network for directed attention and unilateral neglect. Ann Neurol. 1981; 10:309–325.
Mesulam, M-M.Principles of behavioral neurology. Philadelphia: F.A. Davis, 1985.
Nielsen, JM.Agnosia, apraxia, aphasia. New York: Hafner Press, 1965. [(Reprint of 1946 edition).].
Ojemann, GA. Individual variability in cortical localization of language. J Neurosurgery. 1979; 50:164–169.
Semmes, J. Hemispheric specialization: a possible clue to mechanism. Neuropsychologia. 1968; 6:11–26.
Whitaker, HA, Ojemann, GA. Graded localisation of naming from electrical stimulation mapping of left cerebral cortex. Nature. 1977; 270:50–51.
CEREBRAL DOMINANCE
The term cerebral dominance reflects the observation that language functions are usually lateralized to the left hemisphere and visual-spatial functions are usually lateralized to the right hemisphere. Although this propensity for language to lateralize to the left hemisphere is well documented, its biological basis is unknown. There is convincing evidence that left-handers are much less well lateralized than right-handers. Although right-hemisphere dominance for speech is rare in true right-handers, bilateral-hemisphere or right-hemisphere speech representation is common in left-handers. Aphasia after right-hemisphere injury in right-handers is rare (crossed aphasia). Transient aphasia with good recovery is common in left-handers, regardless of the hemisphere injured. As of 1976, Brown and Hécaen (1976) found only nine convincing cases of crossed aphasia in dextrals in the world literature. On the other hand, Zangwill (1960) found that of 54 left-handers with left-hemisphere lesions, 24 (44%) had severe aphasia and 21 (39%) had transient aphasia. Of 39 left-handers with right-hemisphere lesions, 13 (33%) had severe aphasia and 17 (44%) had transient aphasia.
Hemispheric dominance for language may be assessed by a variety of techniques, including the Wada test (intracarotid amobarbital [Amytal] injection), dichotic listening tests, and the effects of unilateral electroshock therapy. Branch et al. (1964) examined dominance for language using the Wada test in 119 patients with intractable epilepsy. Of 48 right-handers, 43 (90%) were left-hemisphere dominant for speech and 5 (10%) were right-hemisphere dominant. The unusually high incidence of right-hemisphere speech dominance reflects the presence of brain injury in a high proportion of the epileptics. Among 71 left-handers, Branch et al. (1964) found 34 (48%) with left-hemisphere speech dominance, reflecting the presence of brain injury in a high proportion of the epileptics. Among the left-handers, evidence of prior left hemisphere injury dropped the frequency of left-hemisphere dominance for speech from 64% to 22%. Thus, early-life left-hemisphere injury strongly influences speech dominance to shift from the left to right hemisphere. However, this injury must occur before six years of age and involve the central language zone for language dominance to reliably shift from left to right.
Dichotic listening studies suggest that speech is less firmly lateralized to the left hemisphere in left-handers than in right-handers. Some evidence suggests that women are less lateralized than men. Based on available evidence, Roberts (1969) concludes that the left hemisphere is dominant for language in at least 95% of right-handers and 66% of left-handers. The right hemisphere is dominant for language in about 30% of left-handers. Bilateral speech representation probably occurs in a small percentage of left-handers and rarely in right-handers. Attempts have been made to relate functional asymmetries (i.e., lateralization of language) to morphological (anatomical) asymmetries of the brain, but such hypotheses remain controversial.
References
Annett, M. Hand preference and the laterality of cerebral speech. Cortex. 1975; 11:305–328.
Benton, AL. Historical notes on hemispheric dominance. Arch Neurol. 1977; 34:127–129.
Branch, D, Milner, B, Rasmussen, T. Intracarotid sodium Amytal for the lateralization of cerebral dominance for speech. J Neurosurg. 1964; 21:399–405.
Briggs, CG, Nebes, RD. The effects of handedness, family history and sex on the performance of a dichotic listening task. Neuropsychologia. 1976; 14:129–133.
Brown, JW, Hécaen, H. Lateralization and language representation. Neurology. 1976; 26:183–189.
Bryden, MP. Tachistoscopic recognition, handedness and cerebral dominance. Neuropsychologia. 1965; 3:1–8.
Dennis, M, Whitaker, HA. Language acquisition following hemidecortication: linguistic superiority of the left over the right hemisphere. Brain Lang. 1976; 3:404–433.
Geffen, G, Traub, E, Stierman, I. Language laterality assessed by unilateral ECT and dichotic monitoring. J Neurol Neurosurg Psychiatry. 1978; 41:354–360.
Geschwind, N. Language and the brain. Sci Am. 1972; 226:76–83.
Geschwind, N, Galaburda, AM. Cerebral lateralization: biological mechanisms, associations, and pathology: I. A hypothesis and a program for research. Arch Neurol. 1985; 42:428–459.
Geschwind, N, Galaburda, AM. Cerebral lateralization: biological mechanisms, associations, and pathology: II. A hypothesis and a program for research. Arch Neurol. 1985; 42:521–552.
Gordon, HW, Bogen, JE. Hemispheric lateralization of singing after intracarotid sodium amylobarbitone. J Neurol Neurosurg Psychiatry. 1974; 37:727–738.
Johnson, O, Harley, C. Handedness and sex differences in cognitive tests of brain laterality. Cortex. 1980; 16:73–82.
Kimura, D. Speech lateralization in young children as determined by an auditory test. J Comp Physiol Psychol. 1963; 56:899–902.
Kimura, D. Cerebral dominance for speech. In: Tower DB, ed. The nervous system, vol. 3. New York: Raven Press; 1975:365–371.
Kimura, D. Spatial localization in left and right visual fields. Can J Psychol. 1978; 23:445–458.
Lake, DA, Bryden, MP. Handedness and sex differences in hemispheric asymmetry. Brain Lang. 1976; 3:266–282.
Lansdell, H. Verbal and nonverbal factors in right-hemisphere speech: relation to early neurological history. J Comp Physiol Psychol. 1969; 69:734–738.
Levy, J. Cerebral lateralization and spatial ability. Behav Genet. 1976; 6:171–188.
McGlone, J. Sex differences in human brain asymmetry: a critical survey. Behav Brain Sci. 1980; 3:215–263.
McGlone, J, Davidson, W. The relation between cerebral speech laterality and spatial ability with special reference to sex and hand preference. Neuropsychologia. 1973; 11:105–113.
Newcombe, F, Ratcliff, G. Handedness, speech lateralization and ability. Neuropsychologia. 1973; 11:399–407.
Obler, LK, Zatorre, RJ, Galloway, L, Vaid, J. Cerebral lateralization in bilinguals: methodological issues. Brain Lang. 1982; 15:40–54.
Penfield, W, Roberts, L.Speech and brain mechanisms. Princeton: Princeton University Press, 1959.
Rasmussen, T, Milner, B. The role of early left-brain injury in determining lateralization of cerebral speech functions. Ann NY Acad Sci. 1977; 299:355–369.
Ratcliff, G, Dila, C, Taylor, L, Milner, B. The morphological asymmetry of the hemispheres and cerebral dominance for speech: a possible relationship. Brain Lang. 1980; 11:87–98.
Roberts, L. Aphasia, apraxia and agnosia in abnormal states of cerebral dominance. In: Vinken PJ, Bruyn GW, eds. Handbook of clinical neurology, vol. 4. Amsterdam: North-Holland; 1969:312–326.
Satz, P. A test of some models of hemispheric speech organization in the left- and right-handed. Science. 1979; 203:1131–1133.
Searleman, A. Subject variables and cerebral organization for language. Cortex. 1980; 16:239–254.
Strauss, E, LaPointe, JS, Wada, JA, et al. Language dominance: correlation of radiological and functional data. Neuropsychologia. 1985; 23:415–420.
Warrington, EK, Pratt, RTC. Language laterality in left-handers assessed by unilateral E.C.T. Neuropsychologia. 1973; 11:423–428.
Zangwill, OCerebral dominance and its relation to psychological function. Edinburgh: Oliver and Boyd, 1960.
Zoccolotti, P, Oltman, PK. Field dependence and lateralization of verbal and configuration processing. Cortex. 1978; 14:155–168.
ANATOMICAL ASYMMETRIES OF THE BRAIN
Right-left anatomical asymmetries have been demonstrated by a variety of investigators. Geschwind and Levitsky (1968) examined the planum temporale in 100 adult brains. The planum temporale corresponds to posterior temporal lobe cortex (on the left side, this area correlates roughly with Wernicke’s area). They found that the left planum temporale was larger than the right in 65% of the brains; in only 11% was the right larger than the left. Cytoarchitectonic studies (Galaburda et al., 1978) have confirmed these gross right-left anatomical asymmetries. Wada et al. (1975) confirmed the anatomical asymmetry noted by Geschwind and Levitsky and demonstrated similar asymmetries in infant and fetal brains. Rubens et al. (1976) studied the course of the sylvian fissure in adult brains. They found that the right sylvian fissure angulated more sharply upward, producing a smaller planum temporale on the right, a higher sylvian point on the right, and a larger inferior parietal lobule on the right. Right-left asymmetries of the brain can also be demonstrated by angiography, pneumonencephalography, or computed tomography. Right-left asymmetries of the brain (similar to those found in humans) can be demonstrated in chimpanzees but not rhesus monkeys. Although it has been suggested that these right-left asymmetries (particularly those noted in the posterior speech region) may explain the propensity for language to lateralize to the left side of the brain, this remains a controversial hypothesis.
Using computed tomography, LeMay (1976) has been able to show that normal patterns of right-left brain asymmetry are more typical of right-handers, whereas reversed patterns of right-left asymmetry are more common in left-handers. However, at this point there is little evidence that right-left asymmetries can predict cerebral dominance for speech (Naeser and Borod, 1986; Koff et al., 1986). Bear et al. (1986) have found that left-right asymmetry of the parietal-occipital region is less frequent in both non-right-handers and in women.
References
Bear, D, Schiff, D, Saver, J, Greenberg, M, Freeman, R. Quantitative analysis of cerebral asymmetries: fronto-occipital correlation, sexual dimorphism and association with handedness. Arch Neurol. 1986; 43:598–603.
Campain, R, Minckler, J. A note on the gross configurations of the human auditory cortex. Brain Lang. 1976; 3:318–323.
Chi, JG, Dooling, EC, Gilles, FH. Gyral development of the human brain. Ann Neurol. 1977; 1:86–93.
Chi, JG, Dooling, EC, Gilles, FH. Left-right asymmetries of the temporal speech areas of the human fetus. Arch Neurol. 1977; 34:346–348.
Galaburda, AM, LeMay, M, Kemper, TL, Geschwind, N. Right-left asymmetries in the brain: structural differences between the hemispheres may underlie cerebral dominance. Science. 1978; 199:852–856.
Galaburda, AM, Sanides, F, Geschwind, N. Human brain: cytoarchitectonic left-right asymmetries in the temporal speech region. Arch Neurol. 1978; 35:812–817.
Geschwind, N, Levitsky, W. Human brain: left-right asymmetries in temporal speech region. Science. 1968; 161:186–187.
Kopp, N, Michel, F, Carrier, H, Biron, A, Duvillard, P. Etude de certaines asymmétries hémisphériques du cerveau humain. J Neurol Sci. 1977; 34:349–363.
Koff, E, Naeser, MA, Pieniadz, JM, Foundas, AL, Levine, HL. Computed tomographic scan hemispheric asymmetries in right and left-handed male and female subjects. Arch Neurol. 1986; 43:487–491.
LeMay, M. Morphological cerebral asymmetries of modern man, fossil man, and non-human primates. Ann NY Acad Sci. 1976; 280:349–366.
LeMay, M. Asymmetries of the skull and handedness: phrenology revisited. J Neurol Sci. 1977; 32:243–253.
LeMay, M, Culebras, A. Human brain morphologic differences in the hemispheres demonstrable by carotid arteriography. N Engl J Med. 1972; 287:168–170.
Branch, CL, Milner, B, McRae, DL. The occipital horns and cerebral dominance. Neurology. 1968; 18:95–98.
Naeser, MA, Borod, JC. Aphasia in left-handers: lesion site, lesion side, and hemispheric asymmetries on CT. Neurology. 1986; 36:471–488.
Pieniadz, JM, Naeser, MA. Computed tomographic scan cerebral asymmetries and morphologic brain asymmetries. Correlation in the same cases post mortem. Arch Neurol. 1984; 41:403–409.
Rubens, AB, Mahowald, MW, Hutton, JT. Asymmetry of the lateral (sylvian) fissures in man. Neurology. 1976; 26:620–624.
Wada, JA, Clarke, R, Hamm, A. Cerebral hemispheric asymmetry in humans: cortical speech zones in 100 adult and 100 infant brains. Arch Neurol. 1975; 32:239–246.
Yeni-Komshian, GH, Benson, DA. Anatomical study of cerebral asymmetry in the temporal lobe of humans, chimpanzees, and rhesus monkeys. Science. 1976; 192:387–389.
LEFT-HANDEDNESS
Estimates of the incidence of left-handedness range from a low of 1% to a high of 30% (Hardyck and Petrinovich, 1977). Using performance measures of handedness, Hardyck and Petrinovich suggest 8% to 10% as a reasonable estimate of left-handedness. A variety of questionnaires have been developed to assess handedness, although Oldfield’s (1971) remains one of the most widely used.
Hardyck and Petrinovich (1977) have emphasized that left-handedness is not a unitary trait.
Left-handers with a family history of left-handedness probably differ from left-handers without such a family history. In general, left-handers without a family history of left-handedness are more strongly left-handed than are those with a family history of it. Furthermore, as a group left-handers are less strongly left-handed than right-handers are right-handed. The basis of this less complete lateralization is not fully understood.
Evidence that left-handers are cognitively deficient as a group is not convincing. Although it has been suggested that some instances of left-handedness reflect early-life brain insult, this view has been disputed. However, certain populations do appear to have an excess of left-handedness (e.g., the mentally retarded, the developmentally dyslexic). Geschwind and Behan (1982) have suggested an interrelationship between left-handedness, autoimmune disorders, migraine, and learning disabilities.
Left-handedness appears to predict anomalous patterns of cerebral organization. Although some left-handers show a normal pattern of central dominance (left-hemisphere dominance for language, right-hemisphere dominance for visual-spatial functions), others show bilateral-hemisphere specialization for language and visual-spatial functions. A minority of left-handers (about 30%) show a reversal of the normal pattern of cerebral dominance found in right-handers. Levy and Reid (1976) have proposed that the writing posture of left-handers may predict cerebral dominance for language. This view has been disputed by Volpe et al. (1981). Aphasia tends to be more mild in left-handers after cerebral injury (regardless of hemisphere injured), and recovery is often more rapid (Brown and Hécaen, 1976). Based on diminished degree of cerebral dominance, it has been hypothesized that spatial ability may be reduced in left-handers (Hicks and Beveridge, 1977).
The incidence of left-handedness (8% to 10%) has remained stable for over 50 centuries (Coren and Porac, 1977). Genetic factors appear to be a powerful determinant of handedness (Carter-Saltzman, 1980). Social and cultural factors may further influence the prevalence of left-handedness.
References
Annett, M. Hand preference and the laterality of cerebral speech. Cortex. 1975; 11:305–328.
Bakan, P. Handedness and birth order. Nature. 1971; 229:195.
Bakan, P. Left handedness and birth order revisited. Cortex. 1977; 15:837–839.
Borod, JC, Carper, M, Naeser, M, Goodglass, H. Left-handed and right-handed aphasics with left hemisphere lesions compared on nonverbal performance measures. Cortex. 1985; 21:81–90.
Brown, JW, Hécaen, H. Lateralization and language representation. Neurology. 1976; 26:183–189.
Carter-Saltzman, L. Biological and sociocultural effects of handedness: comparison between biological and adoptive families. Science. 1980; 209:1263–1265.
Coren, S, Porac, C. Fifty centuries of right-handedness: the historical record. Science. 1977; 198:631–632.
Dusek, CD, Hicks, RA. Multiple birth-risk factors and handedness in elementary school children. Cortex. 1980; 16:471–478.
Geschwind, N, Behan, P. Left-handedness: association with immune disease, migraine, and developmental learning disorder. Proc Natl Acad Sci USA. 1982; 79:5097–5100.
Gesell, A, Ames, LB. The development of handedness. J Genet Psychol. 1947; 70:155–175.
Hardyck, C, Petrinovich, LF. Left-handedness. Psychol Bull. 1977; 84:385–404.
Hécaen, H, de Agostini, M, Monzon-Montes, A. Cerebral organization in left-handers. Brain Lang. 1981; 12:261–284.
Hick, RE, Kinsbourne, M. Human handedness: a partial cross-fostering study. Science. 1976; 192:908–910.
Hicks, RA, Beveridge, R. Handedness and intelligence. Cortex. 1978; 14:304–307.
Hicks, RA, Dusek, CM. The handedness distributions of gifted and non-gifted children. Cortex. 1980; 16:479–481.
Johnson, O, Harley, C. Handedness and sex differences in cognitive tests of brain laterally. Cortex. 1980; 16:73–82.
Levy, J. A review, analysis, and some new data on hand-posture distribution in left-handers. Brain Cogn. 1984; 3:105–127.
Levy, J, Reid, M. Variations in writing posture and cerebral organization. Science. 1976; 194:337–339.
Lishman, WA, McMeekan, ERL. Handedness in relation to direction and degree of cerebral dominance for language. Cortex. 1977; 13:30–43.
Oldfield, RC. The assessment and analysis of handedness: the Edinburgh Inventory. Neuropsychologia. 1971; 9:97–113.
Orsini, DL, Satz, P. A syndrome of pathological left-handedness: correlates of early left hemisphere injury. Arch Neurol. 1986; 43:333–337.
Satz, P. A test of some models of hemispheric speech organization in the left- and right-handed. Science. 1979; 203:1131–1133.
Volpe, BT, Sidtis, JJ, Gazzaniga, MS. Can left-handed writing posture predict cerebral language laterality? Arch Neurol. 1981; 38:637–638.
RIGHT-HEMISPHERE LANGUAGE CAPABILITY
In nearly all right-handers and in about 60% of left-handers, the left hemisphere is dominant for language. The low incidence of crossed aphasia in dextrals is testimony to the rarity of right-hemisphere dominance for language in right-handers.
Several questions arise about right-hemisphere language capability in individuals who are left-hemisphere dominant for language. Can language be transferred to the right hemisphere after left-brain injury? If so, at what cost? What are the linguistic capabilities of the isolated right hemisphere? Does the right hemisphere contribute to language comprehension in non-brain-damaged individuals? Does the right hemisphere contribute to recovery from aphasia after left-hemisphere injury? Evidence from the study of children sustaining left-hemisphere injury early in life suggests that language transfer may occur from left hemisphere to right. This transfer is more likely if injury occurs before six years of age and if the injury involves the classic language areas of either Broca or Wernicke (Rassmussen and Milner,