Unilateral right parietal damage leads to bilateral deficit for high-level motion.

Patients with right parietal damage demonstrate a variety of attentional deficits in their left visual field contralateral to their lesion. We now report that patients with right lesions also show a severe loss in the perception of apparent motion in their "good" right visual field ipsilateral to their lesion. Three tests of attention were conducted, and losses were found only in the contralesional fields for a selective attention and a multiple object tracking task. Losses in apparent motion, however, were bilateral in all cases. The deficit in apparent motion in the parietal patients supports previous claims that this relatively effortless percept is mediated by attention. However, the bilateral deficit suggests that the disruption is due to a bilateral loss in the temporal resolution of attention to transient events that drive the apparent motion percept.

Auditory processing in primate cerebral cortex.

Auditory information is relayed from the ventral nucleus of the medial geniculate complex to a core of three primary or primary-like areas of auditory cortex that are cochleotopically organized and highly responsive to pure tones. Auditory information is then distributed from the core areas to a surrounding belt of about seven areas that are less precisely cochleotopic and generally more responsive to complex stimuli than tones. Recent studies indicate that the belt areas relay to the rostral and caudal divisions of a parabelt region at a third level of processing in the cortex lateral to the belt. The parabelt and belt regions have additional inputs from dorsal and magnocellular divisions of the medial geniculate complex and other parts of the thalamus. The belt and parabelt regions appear to be concerned with integrative and associative functions involved in pattern perception and object recognition. The parabelt fields connect with regions of temporal, parietal, and frontal cortex that mediate additional auditory functions, including space perception and auditory memory.

Impaired syntactic comprehension and production in Broca's aphasia: CT lesion localization and recovery patterns.

Three of 50 patients with left hemisphere stroke manifested Broca's aphasia associated with deficits in syntactic processing. CT demonstrated anterior infarcts in two patients and a posterior infarct in the third. Two years later, all three patients showed improved syntactic production, but only the patient with the posterior lesion performed significantly above change on a sentence comprehension test requiring syntactic manipulations in the absence of semantic constraints. Prospective investigations combining psycholinguistic analyses and brain imaging techniques may provide empiric data relevant to neurologic models of language and ultimately may contribute to patient prognostication and rehabilitation.

Brain size, head size, and intelligence quotient in monozygotic twins.

Many studies of monozygotic (MZ) twins have revealed evidence of genetic influences on intellectual functions and their derangement in certain neurologic and psychiatric diseases afflicting the forebrain. Relatively little is known about genetic influences on the size and shape of the human forebrain and its gross morphologic subdivisions. Using MRI and quantitative image analysis techniques, we examined neuroanatomic similarities in MZ twins and their relationship to head size and intelligence quotient (IQ). ANOVA were carried out using each measure as the dependent variable and genotype, birth order, and sex, separately, as between-subject factors. Pairwise correlations between measures were also computed. We found significant effects of genotype but not birth order for the following neuroanatomic measures: forebrain volume (raw, p < or = 0.0001; normalized by body weight, p = 0.0003); cortical surface area (raw, p = 0.002; normalized, p = 0.001); and callosal area (raw, p < or = 0.0001; normalized by forebrain volume, p = 0.02). We also found significant effects of genotype but not birth order for head circumference (raw, p = 0.0002; normalized, p < or = 0.0001) and full-scale IQ (p = 0.001). There were no significant sex effects except for raw head circumference (p = 0.03). Significant correlations were observed among forebrain volume, cortical surface area, and callosal area and between each brain measure and head circumference. There was no significant correlation between IQ and any brain measure or head circumference. These results indicate that: 1) forebrain volume, cortical surface area, and callosal area are similar in MZ twins; and 2) these brain measures are tightly correlated with one another and with head circumference but not with IQ in young, healthy adults.

The caudal infrasylvian surface in dyslexia: novel magnetic resonance imaging-based findings.

OBJECTIVE: To detect anatomic abnormalities of auditory association cortex in dyslexia by measuring the area of the perisylvian region known as the caudal infrasylvian surface(s) (cIS) in dyslexic and control subjects. BACKGROUND: Several quantitative morphometric investigations of cortical areas in dyslexia have focused on the cIS, which encompasses the supratemporal plane and the inferior bank of the posterior ascending ramus of the sylvian fissure. Inconsistencies in the results of these studies may be attributable in part to the use of measurement methods that do not account fully for surface undulations of the cIS. METHODS: The authors used an MRI-based surface reconstruction technique that models the curvature of the cerebral cortex in three dimensions to obtain whole-hemisphere and regional surface area estimates. Measurements were obtained in both hemispheres of eight right-handed male dyslexic subjects and eight right-handed male control subjects. RESULTS: The cIS area of dyslexic subjects was significantly larger than that of control subjects, and this result was not attributable to a difference in whole-hemisphere surface area. Neither the dyslexic nor control subjects showed a left or right asymmetry in this region, although there was a trend toward less variance of the asymmetry scores in dyslexic subjects. CONCLUSIONS: The gross anatomic organization of this region is different in dyslexic subjects, and elucidation of the precise nature of these differences may be aided by surface modeling techniques.

Musical priming by the right hemisphere post-callosotomy.

The hemispheric representation of auditory functions mediating the perception of harmony in music was investigated in two split-brain patients using a musical chord priming task. Previous experiments in normal subjects had demonstrated that the harmonic context established by a prime chord influences the accuracy of target chord intonation judgements. Only the right hemisphere of each callosotomy patient manifested the normal interaction between harmonic relatedness and intonation. The results raise the possibility that associative auditory functions which generate expectancies for harmonic progression in music are lateralized within the right hemisphere.

Reading with a limited lexicon in the right hemisphere of a callosotomy patient.

The generality of the observation that there is a lexicon present in the right hemisphere of callosotomy patients has been the subject of some dispute. In the series operated on at Dartmouth Hitchcock Medical Center, only two patients have been shown to have a right hemisphere lexicon. This paper reports the existence of a visual and an auditory lexicon in a new patient D.R. and discusses its significance in understanding the role of the right hemisphere in normal and dysfunctional language.

Isolation of a right hemisphere cognitive system in a patient with anarchic (alien) hand sign.

We report evidence of isolated conceptual knowledge in the right hemisphere of a woman with chronic anarchic hand sign after ischemic infarction of the central four-fifths of the corpus callosum. Limited visual information was available to the right hemisphere, access to medial temporal structures subserving memory was disrupted and disconnection from left hemisphere language structures was complete. Still, the right hemisphere could build mental representations of objects via tactile input and use them in cross-modal matching. These representations were not accessed consistently in auditory comprehension or naming tasks. This functional specificity and its pathoanatomical correlates demonstrate that the study of anarchic hand sign can illuminate not just motor control issues but may inform our understanding of the representation and lateralization of conceptual knowledge as well.

Neurobiological foundations for the theory of harmony in western tonal music.

Basic principles of the theory of harmony reflect physiological and anatomical properties of the auditory nervous system and related cognitive systems. This hypothesis is motivated by observations from several different disciplines, including ethnomusicology, developmental psychology, and animal behavior. Over the past several years, we and our colleagues have been investigating the vertical dimension of harmony from the perspective of neurobiology using physiological, psychoacoustic, and neurological methods. Properties of the auditory system that govern harmony perception include (1) the capacity of peripheral auditory neurons to encode temporal regularities in acoustic fine structure and (2) the differential tuning of many neurons throughout the auditory system to a narrow range of frequencies in the audible spectrum. Biologically determined limits on these properties constrain the range of notes used in music throughout the world and the way notes are combined to form intervals and chords in popular Western music. When a harmonic interval is played, neurons throughout the auditory system that are sensitive to one or more frequencies (partials) contained in the interval respond by firing action potentials. For consonant intervals, the fine timing of auditory nerve fiber responses contains strong representations of harmonically related pitches implied by the interval (e.g., Rameau's fundamental bass) in addition to the pitches of notes actually present in the interval. Moreover, all or most of the partials can be resolved by finely tuned neurons throughout the auditory system. By contrast, dissonant intervals evoke auditory nerve fiber activity that does not contain strong representations of constituent notes or related bass notes. Furthermore, many partials are too close together to be resolved. Consequently, they interfere with one another, cause coarse fluctuations in the firing of peripheral and central auditory neurons, and give rise to perception of roughness and dissonance. The effects of auditory cortex lesions on the perception of consonance, pitch, and roughness, combined with a critical reappraisal of published psychoacoustic data on the relationship between consonance and roughness, lead us to conclude that consonance is first and foremost a function of the pitch relationships among notes. Harmony in the vertical dimension is a positive phenomenon, not just a negative phenomenon that depends on the absence of roughness--a view currently held by many psychologists, musicologists, and physiologists.

Music perception and cognition following bilateral lesions of auditory cortex.

We present experimental and anatomical data from a case study of impaired auditory perception following bilateral hemispheric strokes. To consider the cortical representation of sensory, perceptual, and cognitive functions mediating tonal information processing in music, pure tone sensation thresholds, spectral intonation judgments, and the associative priming of spectral intonation judgments by harmonic context were examined, and lesion localization was analyzed quantitatively using straight-line two-dimensional maps of the cortical surface reconstructed from magnetic resonance images. Despite normal pure tone sensation thresholds at 250-8000 Hz, the perception of tonal spectra was severely impaired, such that harmonic structures (major triads) were almost uniformly judged to sound dissonant; yet, the associative priming of spectral intonation judgments by harmonic context was preserved, indicating that cognitive representations of tonal hierarchies in music remained intact and accessible. Brainprints demonstrated complete bilateral lesions of the transverse gyri of Heschl and partial lesions of the right and left superior temporal gyri involving 98 and 20% of their surface areas, respectively. In the right hemisphere, there was partial sparing of the planum temporale, temporoparietal junction, and inferior parietal cortex. In the left hemisphere, all of the superior temporal region anterior to the transverse gyrus and parts of the planum temporale, temporoparietal junction, inferior parietal cortex, and insula were spared. These observations suggest that (1) sensory, perceptual, and cognitive functions mediating tonal information processing in music are neurologically dissociable; (2) complete bilateral lesions of primary auditory cortex combined with partial bilateral lesions of auditory association cortex chronically impair tonal consonance perception; (3) cognitive functions that hierarchically structure pitch information and generate harmonic expectancies during music perception do not rely on the integrity of primary auditory cortex; and (4) musical priming may be mediated by broadly tuned subcomponents of the thala-mocortical auditory system.

Vertebral artery injury and cerebellar stroke while swimming: case report.

A twenty-five year old woman suffered the acute onset of dysequilibrium followed by headache, nausea, vomiting, vertigo, and slurred speech while swimming. Brain imaging revealed a right cerebellar infarct. Intravenous digital subtraction angiography showed a hypoplastic right vertebral artery and focal narrowing of the dominant left vertebral at the level of the C1-C2 junction. The patient was treated with aspirin and dipyridamole and immobilized for two weeks. She achieved almost complete recovery. Repeat angiography showed resolution of the left vertebral artery defect. Other cases of posterior circulation infarction associated with head turning during sports and ordinary activities are reviewed.

Magnetic resonance imaging morphology of the corpus callosum in monozygotic twins.

Recent reports describe wide variations in the size and shape of the human corpus callosum. To investigate genetic influences on this variability, magnetic resonance images from 5 pairs of monozygotic twins and 10 unrelated control subjects were analyzed. Measurements of size and shape revealed greater similarity in twin pairs than in randomly paired controls. The results are consistent with the view that the anatomy of the corpus callosum, while clearly influenced by nongenetic factors, is under considerable genetic control.

Three-dimensional quantitative analysis of hemispheric asymmetry in the human superior temporal region.

The recent observations of overall symmetry of the caudal infrasylvian region by Steinmetz et al. (1990) and Witelson and Kigar (1991, 1992) diverge from earlier findings of leftward asymmetry in this region (Geschwind and Levitsky, 1968; Galaburda et al., 1987; Larsen et al., 1989). To address this inconsistency, we measured the entire infrasylvian surface posterior to Heschl's gyrus from coronal magnetic resonance images of 10 young, normal, right-handed subjects. Computer models were constructed by tracing contours of this region and then interpolating a 3D triangle mesh between each pair of adjacent contours. Measurements of these models showed no significant directional asymmetry. The same contour set was used to obtain measurements with a conventional algorithm that does not interpolate a surface between contours. The results obtained with the second method showed significant leftward asymmetry. These results suggest that in some cases, unbalanced distortions due to folding differences of the hemispheres are sufficient to obtain spurious findings of left-right asymmetry. This supports the claim of Steinmetz and Witelson that leftward asymmetry is restricted to the temporal bank of the caudal infrasylvian surface, and is balanced by rightward asymmetry of the parietal bank.

Surface area of human cerebral cortex and its gross morphological subdivisions: in vivo measurements in monozygotic twins suggest differential hemisphere effects of genetic factors.

Abstract We measured the surEdce area of the cerebral cortex and its gross morphological subdivisions in 10 pairs of monozygotic twins. Cortical surface area was estimated in vivo using magnetic resonance imaging and threedimensional computer models of the intra- and extrasulcal pial surface. The means and standard deviations of regional (e.g., gyral), lobar, hemisphere, and total cortical surface area were tabulated for the entire population of 20 young, right-handed adults (10 females, 10 males). To determine whether genotypic differences were associated with morphometric differences, analyses of variance were carried out on each measure across unrelated twin pairs (genotype factor) and within co-twins (birth order factor). Across unrelated pairs, there was wide variation in regional cortical surface area for the left hemisphere (normalized by total cortical surface area, p ≤ 0.0001) but not for the right hemisphere (normalized, p = 0.12). More variation in lobar surface area was also observed for the left hemisphere (normalized, p = 0.05) than for the right (normalized, p = 0.48). Within co-twins, no signifcant variation in regional surface area or lobar surface area was found for the left or right hemisphere. Although normalized regional and lobar surface area in the left hemisphere differed across unrelated pairs, overall left hemisphere surface area normalized by total cortical surface area did not (p = 0.73). Total cortical surface area normallzed by body weight varied across unrelated pairs (p = 0.001) but not within co-twins (p = 0.39). The effects observed across unrelated pairs were not attributable to sex differences. These results suggest: 1) both the total area and folding of the cortical surface are heavily influenced by genetic factors in humans; and 2) the cerebral hemispheres may be differentially affected by genetic influences on cortical morphogenesis, with the languagedominant left cerebral cortex under stronger genetic control than the right.

Brainprints: Computer-Generated Two-Dimensional Maps of the Human Cerebral Cortex in vivo.

We describe an in vivo method for the quantitative analysis of human necrotical anatomy. The technique allows unfolded regions of functional and morphological interest to be measured planimetrically. Two-dimensional cortical maps and surface area determinations derived from magnetic resonance images of monozygotic twins are presented. In addition, reconstructions and measurements of published post-mortem human and rhesus monkey hemispheres are reported. Potential applications for the study of brain organization in relation to cognitive, motor, and perceptual performance in normal and neurological populations are considered.

Differences in cerebral blood flow and glucose utilization in vegetative versus locked-in patients.

Positron emission tomographic studies of regional cerebral metabolic rate for glucose (rCMRGlc) and cerebral blood flow were performed in 7 vegetative and 3 locked-in patients to determine objectively the level of brain function underlying these clinical states. Cortical gray rCMRGlc in the vegetative patients was 2.73 +/- 0.13 (mean +/- SEM) mg/100 gm/min, less than half the normal value of 6.82 +/- 0.23 (p less than 0.001). Cerebral blood flow exhibited similar but more variable reductions. By contrast, cortical rCMRGlc in the locked-in patients was 5.08 +/- 0.69, a 25% reduction (p less than 0.02) from normal. The massive reduction in vegetative rCMRGlc involved not only the cerebral cortex but also the basal nuclei and cerebellum. Such metabolic hypoactivity has precedent only in deep anesthesia and supports clinical evidence that cerebral cognitive function is lost in the vegetative state, leaving a body that can no longer think or experience pain.