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PubMed1995

Hemispheric asymmetry of event-related potentials in a patient with callosal disconnection syndrome: a comparison of auditory, visual and somatosensory modalities.

To investigate whether callosal lesions affect the distribution of event-related potentials (ERP) between the two hemispheres and whether hemispheric ERP distribution differs among sensory modalities, a patient with interhemispheric disconnection syndrome and 47 controls were subjected to an oddball paradigm. High (target) and low tone bursts for auditory, red (target) and green lights for visual and electrical stimuli delivered to the index (target) or fifth finger for somatosensory ERPs were presented to the unilateral ear, visual field and hand, respectively. The subjects were instructed to press a button with the hand on the stimulated side. The results showed that the hemispheric asymmetry of the patient's auditory ERPs was not significantly different from that of the controls, regardless of which ear was stimulated. In contrast, the visual and somatosensory ERPs showed a delay of the P3 latency and an attenuation of the N1-P2 and N2-P3 amplitude over the hemisphere ipsilateral to the stimulus, regardless of the stimulated side. These findings suggest that the source of P3 generation is relatively lateralized to the hemisphere contralateral to the stimulus, and that the callosal transfer of visual and somatosensory information is involved in the P3 generation in the hemisphere ipsilateral to the stimulus.

Acoustic Stimulation↗
PubMed1989

Neurochemical heterogeneity among corticofugal and callosal projections.

Biochemical, physiological, and anatomical studies over the past 30 years have firmly established glutamate (Glu) as the major neurotransmitter of those cortical neurons which give rise to corticofugal pathways. In the present study we utilized immunohistochemistry, with an antibody directed against Glu, in conjunction with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) histochemistry to examine the Glu-containing neurons which give rise to corticofugal and callosal projections of the rat. Injections of WGA-HRP into the pons labeled cells in layer V of both visual and somatosensory cortices. WGA-HRP-labeled cells which also stained for Glu were large pyramids and in the visual cortex constituted approximately 42% of the total number of neurons which had effectively transported WGA-HRP, while the percentage was 56% in the somatosensory cortex. Following caudate/putamen injections, WGA-HRP-labeled cells were confined to layer V of the somatosensory and motor cortices. Of these cells, 40% in the somatosensory cortex and 53% in the motor cortex were also stained for Glu. Finally, after WGA-HRP injections in the visual cortex numerous WGA-HRP-positive neurons were found throughout layers II-VI around the boundaries between area 17 and areas 18 and 18a of the contralateral hemisphere. Here, 38% of these cells were also labeled for Glu, but this percentage was higher (49%) when layers II-III were considered alone. These findings show that Glu is not the neurotransmitter used overwhelmingly in corticofugal and callosal projections and that different proportions of neurons are Glu-immunoreactive in the systems examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Intra- and interhemispheric processing of visual information in callosal agenesis.

Two siblings with total callosal agenesis were compared with two control groups on a number of tachistoscopic tasks involving unilateral and bilateral presentation of verbal and nonverbal stimuli. Acallosals were able to effect intra- and interhemispheric comparisons and to correctly identify all kinds of stimuli in either visual field. However, they responded more slowly, especially in the bilateral condition where they also made more errors than the controls. The results are interpreted in terms of increased use of extra-callosal commissures.

Adolescent↗
PubMed1991

Absence of disconnexion syndrome in callosal agenesis and early callosotomy: brain reorganization or lack of structural specificity during ontogeny?

Four acallosal subjects, one child, aged 5, and three adults, as well as five epileptic patients who underwent callosotomy between the ages of 6-21 years, were tested on a variety of intra- and intermanual tasks in a study aimed at elucidating the developmental aspects of callosal plasticity. The performance of the clinical sample was compared to that of 48 normal children, aged 5-12 years, an age span generally considered to coincide with the final stages of callosal maturation. As previously reported, interhemispheric integration improved with increasing age in the normal sample. The two patients having undergone callosotomy in childhood performed as well as their normal peers, whereas the three others who had the operation in late adolescence or adulthood showed the typical disconnexion deficits reported in the literature. The acallosal subjects, including the youngest one, outperformed all groups. We speculate that the remarkable plasticity seen in the acallosals and the young callosotomized patients may be related to a critical period in development coinciding with a phase of synaptic overproduction and redundancy that would favor the reinforcement of alternative neural pathways. The compensatory mechanisms appear to become more limited in late adolescence when synaptic distribution presumably assumes adult patterns.

Adolescent↗
PubMed1989

Ten pen men: rhyming skills in two children with callosal agenesis.

Cases of callosal agenesis provide unique opportunities to investigate the normal role of the corpus callosum in the development of cognitive functions, including language. The only language impairment which has been consistently observed in three acallosal patients is on the retrieval of words from rhyming cues. Two new cases of callosal agenesis in children of normal intelligence are presented. Their performance on a variety of rhyming tasks involving both production and recognition of rhyme is reported. Both children display deficits and possible explanations are discussed.

Adolescent↗
PubMed1981

Evidence that the early postnatal restriction of the cells of origin of the callosal projection is due to the elimination of axonal collaterals rather than to the death of neurons.

By using two fluorescent dyes that are retrogradely transported along axons, we have been able to demonstrate that many of the neurons in the parietal region of the rat cerebral cortex that can be labeled from the contralateral hemisphere early in postnatal development, persist well beyond the period when the callosal projection normally becomes restricted. This indicates that the major factor in the progressive restriction of the callosal projection is the withdrawal or degeneration of axon collaterals, rather than the selective death of many of the cells that initially project to the opposite side.

Animals↗
PubMed1983

Cortico-cortical connections reorganize in hamsters after neonatal transection of the callosal bridge.

Neonatal hamsters were subjected to transection of the callosal bridge. Later examination of the brains showed complete or partial absence of the corpus callosum and an anomalous bilateral longitudinal bundle of fibers. In addition, aberrant commissural fibers were seen to connect heterotopically the parietal cortex with the contralateral frontal cortex through a callosal remnant over the septum, and the olfactory cortex with the opposite frontal and parietal cortices through the anterior commissure.

Aging↗
PubMed1993

Neuronal responses to vestibular and callosal stimulation in the anterior suprasylvian gyrus of the cat.

Neuronal responses to electrical stimulation at the horizontal ampulla (HA), vestibular nerve (at the windows) and corpus callosum (CC) were investigated in neurons in the anterior suprasylvian gyrus of the cat. The field potentials to HA stimulation had short latency: 2.9 +/- 0.3 (mean +/- SD) ms from the stimulus to the onset and 5.6 +/- 1.9 ms to the peak. The focus of the evoked potentials was located in the anterior suprasylvian (ASS) gyrus or near the ASS sulcus. HA stimulation activated 6 neurons out of 674 examined, with the mean latency of 4.3 +/- 1.1 ms. Of these 6, four neurons also responded to window stimulation. Fifty-six neurons responded to window stimulation with the mean latency of 6.1 +/- 2.4 ms. The mean latency for CC stimulation was 1.9 +/- 0.9 ms (n = 76). Four neurons responded to CC stimulation antidromically (mean = 0.9 +/- 0.3 ms) and one of them also responded orthodromically. The convergence of CC inputs in relation to HA or window stimulation was examined. One (17%) of the 6 HA-activated cells responded to CC stimulation, compared with 8 (14%) of the 56 neurons activated by window stimulation. The other 612 neurons did not respond to either HA or window stimulation, and 80 (13%) of the 612 responded to CC stimulation. Therefore, it is concluded that neurons in the ASS gyrus received callosal input equally irrespective of the presence or absence of responses to ampulla or window stimulation. WGA-HRP was injected in the ASS gyrus to identify the passing callosal fibers in the CC. Fibers from the ASS area passed at the rostral third of the CC. The present results indicate that the ASS area received vestibular projection with short latency, but responses of this projection did not seem to be very strong, at least from the present unit study, to HA stimulation. Discussion was made on the poor neuronal responses to electrical HA stimulation in comparison with previous studies. Also consideration was made on neuronal activity to CC stimulation.

Animals↗
PubMed1980

Distribution of callosal fibers around the hand representations in monkey somatic sensory cortex.

Single or multiunit recording of responses to natural peripheral stimuli was used to map the representations of the upper limb and adjacent body parts in the postcentral gyrus of monkeys in which callosally projecting cells and/or axons had been prepared for labeling by previous section of the corpus callosum or contralateral injection of horseradish peroxidase. Subsequent demonstration of electrode tracks in relation to labeled cells and axons showed that no neurons with receptive fields distal to the elbow lay in callosally connected zones, irrespective of the cytoarchitectonic field or body representation in which they lay.

Afferent Pathways↗
PubMedDate not supplied

Do callosal projection neurons reflect sex differences in axon number?

We have reported that female rats have more axons in the splenium of the corpus callosum than do male rats (12). To determine if the greater number of axons found in female rats might be reflected in a larger distribution of callosal projection neurons, horseradish peroxidase (HRP) was injected into the visual cortex of 55-65-day-old rats of both sexes that had been housed in a complex environment since weaning. The pattern of labeled neurons was examined in tangential sections in the cortex contralateral to the injection site, and three-dimensional reconstructions were quantified at the area 17/18a border and in area 18b. Male and female rats were found to have indistinguishable distributions of labeled callosal projection neurons. The present study failed to find an obvious difference in the distribution of projection neurons as the basis for the sex differences in axon number, but because of the limitations of tracing techniques, subtle differences cannot be excluded.

Animals↗
PubMed2006

Ipsilateral silent period: a marker of callosal conduction abnormality in early relapsing-remitting multiple sclerosis?

OBJECTIVE: The corpus callosum (CC) is commonly affected in multiple sclerosis (MS). The ipsilateral silent period (iSP) is a putative electrophysiological marker of callosal demyelination. The purpose of this study was to re-assess, under recently established optimised protocol conditions [Jung P., Ziemann U. Differences of the ipsilateral silent period in small hand muscles. Muscle Nerve in press.], its diagnostic sensitivity in MS, about which conflicting results were reported in previous studies. METHODS: ISP measurements (onset, duration, and depth) were obtained in the abductor pollicis brevis (APB) muscle of either hand in 49 patients with early relapsing-remitting MS (RRMS) (mean EDSS, 1.3). Standard central motor conduction times to the APB (CMCT(APB)) and tibial anterior muscles (CMCT(TA)), and magnetic resonance images (MRI) were also obtained. RESULTS: ISP measurements showed a similar diagnostic sensitivity (28.6%) as CMCT(APB) (24.5%), while diagnostic sensitivities of CMCT(TA) (69.4%) and MRI of the CC (78.6%) were much higher. Prolongation of iSP duration was the most sensitive single iSP measure. ISP prolongation occurred more frequently when CMCT(APB) to the same hand was also prolonged (40.0% vs. 8.4%, p<0.0001). The correlation between iSP duration and CMCT(APB) was significant (Pearson's r=0.24, p<0.02), suggesting that iSP duration can be contaminated by demyelination of the contralateral corticospinal tract. ISP duration did not correlate with MRI abnormalities of the CC. CONCLUSIONS: ISP measures are neither a sensitive nor a specific marker of callosal conduction abnormality in early RRMS.

Adult↗
PubMed2006

Spatial resolution dependence of DTI tractography in human occipito-callosal region.

Diffusion tensor imaging (DTI) and fiber tracking have been used to measure the fiber structural connectivity in humans in a non-invasive manner. However, low sensitivity is a principal limitation of these methods, causing a large number of possibly missing fiber tracts (FTs). Here we studied how the spatial resolution affects the sensitivity of the fiber tracing by rescaling data to different resolutions. Our data suggest that the spatial resolution can change the degree of the asymmetric cross-callosal connections in the lower visual field (loVF) compared to the upper visual field (upVF). Among connections from loVF, a larger voxel size resulted in a smaller number of FTs that was not commensurate to the number of seed points, while the number of connections from upVF was not significantly affected by variation in seeding point numbers. We conclude from our study that the spatial resolution of the acquired data will have to be taken into consideration in interpreting DTI fiber tracking data. Our results further suggest that the acquisition resolution of around 2 mm iso-voxel in the conventional DTI scheme can reconstruct the asymmetric upper and lower white matter structure in occipito-callosal region.

Adult↗
PubMed2003

Callosal lesions and behavior: history and modern concepts.

Callosotomy has played a unique role in the treatment of epilepsy and in the understanding of human brain function. The pioneering work of Dejerine and Liepmann presenting the first findings of callosal lesion pathology at the turn of the 20th century was accepted but then quickly forgotten. Two schools resurrected the phoenix of callosal syndromes: Roger Sperry and Michael Gazzaniga leading in experimental neuroscience, and Norman Geschwind leading in clinical neurology. Callosotomy remains an effective technique to treat atonic, tonic, and tonic-clonic seizures, especially in patients with symptomatic generalized epilepsies such as Lennox-Gastaut syndrome. Neurologic, cognitive, and behavioral complications limit its use given that precise characterization of these complications as well as their frequency is difficult. The high frequencies of developmental delays, severe seizures, head injuries, antiepileptic drug burden, and other factors limit the ability to attribute a specific change to surgical intervention, since surgery can change multiple factors. For example, subtle behavioral changes in executive function and personality are difficult to delineate in a population with preexisting neurologic and psychiatric disorders. Despite this, a clearer picture of the effects of callosotomy, as defined by clinical neurology and neuropsychology as well as cognitive neuroscience, is emerging.

Animals↗
PubMed1997

The fates of the callosal neurons in neocortex after bisection of the corpus callosum, using the technique of retrograde neuronal labeling with two fluorescent dyes.

The fate of callosal neurons after callosotomy is yet unclear although this has become a common surgical procedure for intractable generalized epilepsies. Using retrograde neuronal labeling with two fluorescent dyes, we demonstrated that callosal neurons in the parietal cortex of the adult rat survive up to 20 weeks after callosotomy. Our data suggest that these neurons possess numerous ipsilateral axon collaterals with indispensable functions in the ipsilateral hemisphere.

Amidines↗
PubMed1997

Alien hand syndrome: influence of neglect on the clinical presentation of frontal and callosal variants.

Three patients with mesial frontal and extensive callosal lesions due to anterior cerebral artery infarction manifested an alien hand syndrome (AHS) with varied features. Patient 1 with left hemispheric lesion showed right hand's impulsive reaching and grasping and left hand's antagonistic movements to the right (intermanual conflict; IMC). Patients 2 and 3 with right hemispheric lesion manifested a left hemihypokinesia which was thought to have suppressed the frequency and amplitude or even the occurrence of left hand's reaching and grasping. IMC and other left hand's non-antagonistic, irrelevant movements to the right remained. Because the term "IMC" is often misused and not strictly defined, its association with right hand's reaching and grasping is quite uncommon, its significance as a sign of callosal disconnection is not well validated, and because left hand's reaching and grasping tend to be suppressed by motor neglect, a trend may then develop for the right hand to be the sole focus of pathological behaviour in patients with the so-called frontal AHS (Feinberg, Schindler, Flanagan et al., 1992).

Aged↗
PubMed2006

Right unilateral jargonagraphia as a symptom of callosal disconnection.

We report the case of a right-handed patient who exhibited right unilateral jargonagraphia after a traumatic callosal hemorrhage. The lesions involved the entire corpus callosum, except for the lower part of the genu and the splenium. The patient's right unilateral jargonagraphia was characterized by neologisms and perseveration in kanji and kana, and was more prominent in kana than kanji. The jargonagraphia was similar to that observed in crossed aphasia, except that agraphia occurred only with the right hand. The patient also showed right unilateral tactile anomia and right tactile alexia, along with right-ear extinction on a dichotic listening test for verbal stimuli, which suggested that language function was lateralized to the right hemisphere. Since this patient had learned to write with his right hand, kinesthetic images of characters were thought to be formed and stored dominantly in the left hemisphere. We suggest that the callosal lesions disturbed the interhemispheric transfer of information for the dual-route procedures for writing in the right hemisphere, allowing the kinesthetic images of characters stored in the left hemisphere to be processed freely, resulting in the right unilateral jargonagraphia. At least two factors seem to explain that kana was more defective than kanji. First, writing in kana, which is assumed to be processed mainly via a sub-word phoneme to grapheme conversion route, might depend more strongly on lateralized linguistic processing than writing in kanji. Second, kanji, which represent meaning as well as phonology, with much more complicated graphic patterns than kana, are assumed to be processed in both hemispheres.

Accidents, Traffic↗
PubMed2001

The stability of compromised interhemispheric processing in callosal dysgenesis and partial commissurotomy.

The persistence and stability of selective deficits in interhemispheric processing resulting from known callosal pathology have been monitored over periods ranging from ten to thirty five years. The present study included five patients: two with complete agenesis of the corpus callosum, one with partial dysgenesis, and two with a partial section of the corpus callosum. A crossed-uncrossed difference task and four bilateral visual matching tasks were administered to these patients and to groups of normal individuals matched on age and intelligence. As expected, all of the patients showed deficits in speed or accuracy relative to the performance of their control groups. The profile of performance for each patient across the five tasks demonstrated a systematic (but not perfectly consistent) relationship with the location and extent of callosal pathology.

Adolescent↗
PubMed2000

Dissociation between distal and proximal left limb agraphia and agraphesthesia in a patient with a callosal disconnection syndrome.

A few neuropsychological studies have suggested the existence of bilateral hemispheric representations for the proximal parts of the limbs in humans. We report the case of a patient who presented with a callosal disconnection syndrome, which at a later stage of disease became restricted to left agraphia, left agraphesthesia and left auditory extinction. The anomic character of the agraphesthesia was demonstrated. Tactile naming was normal, which allows us to conclude that separate callosal pathways related to the left language areas transmit information for graphesthesia and tactile naming. Agraphia and agraphesthesia were not observed when the proximal part of the left upper limb was utilized. These observations support the conclusion that writing and graphesthesia with the proximal part of the limb can be mediated by the ipsilateral cortex.

Agraphia↗