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PubMed1996

Sexual dimorphism in the human corpus callosum? A comparison of methodologies.

Mid-sagittal magnetic resonance images of 104 normal individuals were analyzed to assess whether or not the corpus callosum or parts thereof is sexually dimorphic in favor of females. Subjects were 56 males and 48 females, both groups being closely age matched. The outline of the corpus callosum was divided into seven subareas, using three different orientations. A comparison was made between subareas with the divisions based on different orientations. Results showed significant differences (P < 0.05) in all cases, with one exception in females. No significant sexual dimorphism was found, with the exception of one subarea in one of the orientations which was significantly larger in males. No significant correlation was found between corpus callosal area and either cerebral hemispheric area or an estimate of cranial capacity. Relative measures, incorporating these two brain size indicators as covariates, also showed no significant sexual dimorphism. In conclusion, no sexual dimorphism of the human corpus callosum favoring females was found in this study, and it appears that inadequate sampling, differing feature orientation, and inappropriate size correction procedures may have been factors responsible for conflicting results in previous studies.

Adult↗
PubMed1984

Interhemispheric transfer of voluntary motor commands in man.

The lack of callosal fibres between homotopic areas of the hand in the sensorimotor cortex in man and its possible functional correlates were investigated in normal adult subjects by comparing simple reaction times (RTs) of voluntary movements triggered by a somaesthetic stimulus to the same or opposite side of the body. An air jet was delivered to the skin of distal (index finger) or proximal (shoulder) ipsi- or contralateral zones, and triggered voluntary extension of the index finger or flexion of the forearm. The RT was measured from the arrival of the stimulus to the skin to the onset of the surface EMG of the muscle extensor indicis proprius or biceps brachii. The RTs of the contralateral finger movements triggered by either proximal or distal skin stimuli were significantly longer than the RTs of the corresponding ipsilateral movements (mean difference 11.72 and 15.10 msec respectively). When the task was flexion of the forearm, the differences in RTs between contra- and ipsilateral movements were instead compatible with a transcallosal transfer (mean difference about 2 msec in both cases). It is concluded that transcallosal connections between hand sensorimotor areas are conceivably absent also in man. Furthermore, the delay in contralateral distal performance appears to be due to a lack of transfer of the command through the motor areas, rather than to a lack of transfer of the triggering cutaneous afferent information to the performing hemisphere.

Adult↗
PubMed1987

Transcallosal response (TCR) in the chronic photosensitive baboon preparation, Papio papio. II. Effect of premotor cortical kindling.

The chronological pattern of transcallosal response (TCR) and its recovery cycle were studied by single or paired stimulation of the homotopic primary and the secondary (contralateral) cortical site before, during and after primary site premotor cortical kindling in Papio papio. Prior to kindling, the sequential pattern of TCR was early positive (P1), negative (N1), late small positive (P2) and large negative (N2) components. The recovery cycle of both P1 and N1 showed a marked supernormal phase at an inter-stimulus interval of 15-200 msec with a peak at about 30 msec, showing maximal facilitation up to 300%. Kindling, with or without prior low frequency cortical stimulation, resulted in a long-lasting amplitude potentiation of both P1 and N1 and a significant modification of the late components. However, a transient amplitude reduction was noted immediately following completion of stage 5 kindling, presumably due to repeated generalized convulsions. These changes occurred only during primary (kindling), but not secondary, homotopic site stimulation. These findings suggest that a persistently increased callosal transmission is probably due to primary site kindling-induced functional alteration of the synaptic site at the homotopic secondary site cortex. In contrast, the supernormal phase of the TCR recovery cycle was suppressed significantly at the secondary site cortex. Since a similar suppressive effect was observed with a small dose of pentobarbital in naive baboons, kindling is considered to produce enhancement of the inhibitory mechanism. However, a diminished suppressive effect on the supernormality 20 days after the termination of kindling suggests that this suppressive effect is transient. It is probably related to the repeated kindled convulsive seizures rather than to the kindling process itself.

Animals↗
PubMed1984

Deafferentation of the visual cortex: the effect on cortical cells in normal and in early monocularly deprived cats.

The optic tract was unilaterally transected and receptive field mapping and unit recordings were made for cells in the boundary of areas 17-18 in the deafferented and in the intact visual cortex of adult cats monocularly deprived during the critical developmental period. Three groups of adult animals served as controls: normal cats, early monocularly deprived (MD) cats, and optic tract transected cats. In contrast to the activity found in the intact hemisphere, the deafferented hemisphere of the experimental group was almost completely unresponsive. The ocular dominance distribution in the intact hemisphere of the experimental group (75.0% cells monocularly driven by the normal eye) was similar to that of the control MD cats (78.1%). This indicates that cutting the optic tract after the critical period does not affect the ocular dominance distribution of cortical cells induced in the intact hemisphere by early monocular deprivation. The reduction found in the proportion of visually responsive cells and the orientation and direction selective cells in the intact hemisphere of the experimental group, is mainly due to the isolation of the fellow hemisphere from its direct visual input, and the subsequent inactivation of the callosal pathway interconnecting the two visual areas.

Afferent Pathways↗
PubMed1984

Effects of fasting during gestation on brain development in BALB/c mice.

The development of the corpus callosum (CC) was examined in BALB/cCF mice in relation to the effects of a 32-h period of maternal fasting. The treatment was imposed on days 15 and 16 during gestation, which immediately precedes the time when the initial callosal axons cross the midline. The BALB/c strain was used because it is prone to developing a corpus callosum which is either small in size or absent at the midline. A split-litter design was used where fetal brain development was assessed on days 22 and 50 postconception (birth and weaning). The treatment did not increase the incidence of absent CC. On day 22 the midsagittal cross-sectional area of the CC, as well as brain and body weight, were smaller in the experimental group. Covariance analysis showed the effect on brain weight to be related to the overall growth retardation seen in the low body weight. In the control group, CC area and the brain weight were positively correlated, but in the experimental group this was not the case, suggesting the effect on the CC was independent of growth retardation. By day 50 there were no significant differences between the groups on any measure, although the data did show a trend toward a smaller CC in the fasted animals.

Aging↗
PubMed1985

Regeneration of central nervous system axons into an acellular tube in the absence of distal tissue.

To differentiate between local and distant influences on central nerve regeneration, an impervious, stainless-steel cannula, 12 mm long, was placed in the path of severed axons within the corpus callosum of adult rats. The cannula was occluded for 1 week after implantation to prevent herniation of tissue into its lumen. The extracranial end of the tube was plugged with Gelfoam rather than tissue. Inflammatory cells within the tube decreased in number with time and all animals survived for the experiment's duration of 4 to 16 weeks. Some callosal axons grew into the cannula and eventually extended about 1.3 mm. After 8 to 16 weeks, the lumen of the cannula contained many unmyelinated axons, some of which formed fascicles, myelinated axons, demyelinating axons, a few oligodendrocytes, and many astrocytic processes, macrophages, and blood vessels. A striking feature was the linear orientation of cells and their processes. The distal tip of the core resembled a central nervous system explant: it included an appreciable number of growth cones, synaptic terminals embedded in a generous extracellular space, and occasional remyelinating axons. Thus, within an impervious, acellular conduit and in the absence of distal tissue, intrinsic, neuronal processes can be redirected, fasciculate, myelinate, and can regrow alongside glia and endothelium. An indwelling tube, isolating the growth from surrounding brain fluid, may permit assessment of glial, neuronal, and extracellular contributions to the directed regeneration of adult, central axons.

Animals↗
PubMed1985

Dorsal hippocampal kindling and transfer in split-brain rats.

The rate of kindling of a primary site in the dorsal hippocampus of rats was not altered by various forebrain commissurotomies or midbrain bisection. The positive transfer in the kindling of a secondary site in the homotopic hippocampus, on the other hand, was abolished by extensive forebrain transection, whereas anterior callosal or midbrain bisection alone was ineffective. In addition, there was no evidence of an interference effect when rekindling the original primary site. These results have important implications for interhemispheric mechanisms in kindling.

Animals↗
PubMed1987

Role of the corpus callosum and hippocampal commissure on transfer phenomenon in amygdala-kindled cats.

Forebrain-bisected cats underwent kindling at primary and secondary amygdala sites. The behavioral effect of amygdala kindling was then examined according to the extent of the surgical lesion in the forebrain commissures. Bisection of the corpus callosum with or without lesion of the hippocampal commissure modified both kindling and kindled symmetrical generalized seizure into a lateralized and asymmetrical form. Lesion of the hippocampal commissure was correlated with the loss of the expected positive transfer effect at the secondary amygdala site. These results suggest that whereas the corpus callosum plays a major role in patterning convulsive generalization and generalized convulsion, the hippocampal commissure is involved in mediation of the transhemispheric positive transfer effect. Evidence of a callosal inhibitory influence on amygdala kindling was not obtained.

Amygdala↗
PubMed1995

Transient resolution of bilateral tremor after unilateral thalamotomy, associated with focal injury of the corpus callosum: case report.

We present a patient with Parkinson's disease whose bilateral tremor transiently resolved after a unilateral left ventrolateral thalamotomy. The transient resolution of the bilateral tremor was associated with a focal thalamic lesion and a second lesion in the corpus callosum. The mechanism of this phenomenon may be related to temporary disruption of descending bilateral corticostriate projections by the callosal lesion.

Corpus Callosum↗
PubMed1995

Corpus callosum atrophy in amyotrophic lateral sclerosis.

Recent studies have suggested widespread involvement of the cerebral regions other than the primary motor cortex in amyotrophic lateral sclerosis. To investigate atrophy of the corpus callosum as a measure of cerebral pathology, we studied 25 right-handed patients with sporadic amyotrophic lateral sclerosis using magnetic resonance imaging. Five patients had cognitive decline or emotional and personality changes. The ratios of mid-sagittal corpus callosum areas to the midline internal skull surface area on T1-weighted images were analysed. Compared with 25 age- and sex-matched right-handed control subjects, the patients had significantly decreased callosal/skull area ratio, with anterior predominance of the degree of atrophy. The patients with cognitive decline or psychiatric symptoms had substantial atrophy of the anterior fourth of the corpus callosum. These findings suggest that atrophy of the corpus callosum, especially in the anterior half, is present in amyotrophic lateral sclerosis, and that severe atrophy in the anterior fourth is associated with cognitive decline and psychiatric symptoms. Callosal atrophy may reflect the widespread distribution of pathological changes in the cerebral cortex, which are accentuated in the frontal cortex.

Adult↗
PubMed1996

An autopsy case of Marchiafava-Bignami disease with peculiar chronological CT changes in the corpus callosum: neuroradiopathological correlations.

We conducted a comparative analysis of the autopsy findings in a case of Marchiafava-Bignami disease with the X-ray computed tomography (CT) and magnetic resonance imaging (MRI) findings obtained while the patient was alive. Histologically, massive deposits of hemosiderin were demonstrated in the astrocytes and macrophages located in the walls of the callosal cystic lesion, suggesting that the transient increase in density during the subacute stage observed on X-ray CT is secondary to significant hemorrhage.

Adult↗
PubMed1982

Naloxone-induced epileptogenesis has brain-site specificity in rats.

Naloxone injected into the lateral septum caused intense electrocortical seizures which did not occur following callosal or periaqueductal gray (PAG) injections. Conversely, injections into periaqueductal gray caused a characteristic and pronounced backward circling with only moderate electrocortical changes. Intracerebral injection of naloxone had effects, including epileptogenesis, which appeared to be site-specific. These effects are in some ways similar to the effects of enkephalin and morphine.

Animals↗
PubMed1982

Information processing deficits in hydrocephalic and letter reversal children.

Hydrocephalic, letter reversal and normal children were tested with a tactile matching-to-sample task, a tachistoscopic matching-to-sample task, and a dichotic listening paradigm. For hydrocephalics, intrahemispheric as well as interhemispheric errors occurred; the partial callosal hypothesis was not supported. Letter reversal children demonstrated an interhemispheric deficit only in tactile performance.

Child↗
PubMed1984

Visual evoked potentials to lateralized visual stimuli and the measurement of interhemispheric transmission time.

Visual evoked potentials (VEPs) to lateralized light flashes were recorded from the parietal midline, and from homologous occipital and central sites, in a GO/ NOGO reaction time task. The N160 component of the VEP was found to be larger over the hemisphere contralateral to the visual field of stimulus exposure at all pairs of lateral electrodes. At the occipital sites only, N160 latency was also shorter from the contralateral hemisphere, by an average of approximately 14 msec. This was not so centrally, where a non-significant value of approximately 4 msec was obtained. These data are considered to be consistent with Milner and Lines' hypothesis that callosal transmission occurs at different rates in different functional regions of the corpus callosum.

Cerebral Cortex↗
PubMed1984

Lateral specialization and verbal/spatial ability in preschool children: age, sex and familial handedness differences.

One hundred and fifty-five preschool children between 2 1/2 and 5 1/2 yr of age were administered two dichotic tests (digit and nonverbal sound) and three Wechsler Intelligence subtests (vocabulary, geometric design and block design). The familial dextral (FD) children around 4 yr and older demonstrated a greater degree of absolute ear laterality than the FD children under 4 yr of age. There were also age-related changes in the relationship between children's ability scores and their ear laterality scores. For older FD children a greater right-ear advantage for verbal stimuli and a left-ear advantage for nonverbal stimuli was associated with higher vocabulary scores. Under 4 yr of age, however, a strong right-ear advantage for verbal stimuli was associated with relatively higher spatial than vocabulary ability. For these younger FD children, less marked laterality predicted higher vocabulary scores. It is hypothesized that a cortical organizational transition is occurring around 4 yr of age and that this transition involves a shift from reliance on subcortical to cortical mediation, accompanied by increasing callosally mediated inhibition and integration of hemispheric function. Furthermore, there were sex differences observed in the relationship between lateral specialization and spatial ability. As young as 2 1/2 yr of age, the FD boys' spatial ability scores were positively associated with having a left-ear advantage for nonverbal sound stimuli. The FD girls' spatial ability scores were not significantly related to their ear advantage scores for nonverbal sounds but were associated with their ear advantage scores for verbal stimuli. In addition, around 4 yr of age a shift was observed in the relationship between the boys' absolute laterality scores and the difference between their spatial and vocabulary ability scores which was not found for the girls' scores. It it suggested that the maturation of right hemispheric spatial mediation may be delayed or inhibited in girls.

Auditory Perception↗
PubMed1984

Neuropsychological demonstration of splenial interhemispheric disconnection in a case of "optic anomia".

A patient is described whose neuropsychological deficit corresponded to the notion of "optic aphasia" or, better, optic anomia. The functional deficit was undirectional, i.e. there was a severe impairment in the naming of visually presented stimuli without impairment in the comprehension of the corresponding names. The splenial disconnection was demonstrated by intact cross modal matching within the right hemisphere as well as preserved left-handed tactile naming, which is processed via mid-callosal pathways. The psychological interpretation is discussed in terms of visual and tactile semantics, considering also the presumably diffuse cerebral organization of semantic fields.

Aged↗
PubMed1988

Crossing the midline by four to eight year old children.

In Experiment 1 children (Kinder, 4-5 yr; Prep, 5-6 yr; Grade 1, 6-7 yr; Grade 2, 7-8 yr) bisected horizontal lines placed to the left, right or across the midline. The youngest groups displayed symmetrical neglect, erring to the left with the left hand and to the right with the right, the adult pattern of leftwards error not appearing until about Grade 2. However, while Prep, Grade 1 and Grade 2 sinistrals showed bigger between-hand differences than dextrals, this was not, unlike an earlier study, true of the youngest Kinder group, and symmetrical neglect did not appear to be peculiar to young sinistrals. A timed peg-moving task in Experiment II showed that performance did not slow when crossing the midline; nor did young sinistrals perform better with centrifugal abductive movement. These and other findings were incompatible with the idea of callosal immaturity in young sinistrals.

Analysis of Variance↗
PubMed1989

Differential-handed response to verbal and visual spatial stimuli: evidence of specialized hemispheric processing following callosotomy.

Left- and right-hand responses were studied in a patient who had undergone complete corpus callosotomy to examine selective hemispheric processing employing free-field stimuli. Tests of verbal and visual spatial processing were presented, and multiple choice performances were obtained using both left and right hands. A double dissociation emerged, with superior left-handed performance on visual spatial tasks, and better right-handed performance on verbal tasks. In addition, the patient displayed hemispatial dyscalculia in which he solved written arithmetic problems disregarding free-field numerical information presented toward his left. Evidence of multimodality left-sided extinction was also present. Further, despite unilateral callosal apraxia, the left hand displayed superiority during a continuous performance task. These results demonstrate that specialized functions of the cerebral hemispheres may be observed for response output in the absence of restricted hemispheric input, and that components of the neglect syndrome may be seen following corpus callosotomy.

Adult↗