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PubMed1994

Interhemispheric interaction in children of 7-8: analysis of EEG coherence and finger tapping parameters.

To investigate interhemispheric interaction (IHI), the EEGs of 42 children between the ages of 7-8 years were recorded while they were performing, as fast as possible, both unimanual and bimanual rhythmic tapping tasks. As an EEG index of IHI we used coherence values (Coh) in the alpha band in the pairs of leads F3/F4, C3/C4, P3/P4, O1/O2, and T3/T4 during resting and tapping. The difference between left hand (L-L) and right hand (R-R) intertap intervals in comparable conditions was though to reflect IHI. Interhemispheric alpha Coh increase was only evident in bimanual rhythmic tasks, and was confined to the C3/C4 and P3/P4 regions. Coh in these brain areas correlated negatively with the time difference between the L-L and R-R intertap intervals. The results show that interhemispheric alpha Coh. can be regarded as an index of IHI during bimanual tapping, and support the clinical hypothesis that bimanual versus unimanual tapping might reflect interhemispheric or callosal function.

Alpha Rhythm↗
PubMed1994

Interhemispheric sharing of visual memory in macaques.

(1) In macaques with the optic chiasm transected, and forebrain commissural communication limited to the anterior commissure or the posterior 5 mm of the splenium of the corpus callosum, visual patterns viewed initially by only one eye (hemisphere) are subsequently recognized by the other with normal accuracy. (2) The efficiency of these commissural paths is further indicated by the fact that even when as many as six "target" images are presented for memorization to only one hemisphere, it makes essentially no difference as to accuracy or latency of performance which hemisphere is then required to distinguish "target" from "non-target" images. (3) By electrically tetanizing structures in one or the other temporal lobe at various times in relation to visual input and/or mnemonic testing it could be shown: (a) that a memory trace restricted in its formation to a single hemisphere was available to the other via either forebrain commissure, and (b) that the memory is formed bilaterally despite unilateral input. (4) When the chiasm is split but the commissures are intact, simultaneous presentation of disparate images to each hemisphere severely perturbs performance, suggesting that the callosal system operates continuously to unify visual percepts; but when only the anterior commissure is intact, the two hemispheres accept incongruent images without perturbation. (5) In the fully "split-brain" condition, when one hemisphere cannot access memories held in the other, the accuracy of performance by each hemisphere is nevertheless burdened by the memory load of its neocortically disconnected partner. It can thus be inferred that the brainstem plays a critical, unifying role in this mnemonic process.

Animals↗
PubMed1994

Visual hemispheric dominance induced in split brain cats during development: a model of deficient interhemispheric transfer derived from physiological evidence in single visual cortex cells.

The effects of cancellation of both interhemispheric callosal transfer and interocular interactions, were studied in early monocularly deprived cats. The main purpose of this study was therefore to prove whether unilateral hemispheric dominance would result under these conditions and to what extent each hemisphere will be functionally independent. Secondly, we have attempted to establish such an experimental model physiologically, on the single cell level. Interhemispheric transfer was surgically canceled by sagittal transection of the corpus callosum. In addition, the ocular projections were separated by sagittal transection of the optic chiasm in the transbuccal approach. This condition had practically induced visual split brain condition in these cats. These manipulations were carried out concurrently with monocular deprivation (SBDK group) which was surgically done by eye closure during the critical period of development of the visual system. Thus, the hemisphere ipsilaterally to the visually deprived eye had developed under conditions of deficient visual experience while the hemisphere ipsilaterally to the normal eye had developed under conditions of unaltered visual experience. A group of cats (SBK) similarly operated but equally binocularly exposed during development was served as controls. In addition, adult cats similarly operated during adulthood either chronically or acutely were studied to evaluate the effects of interhemispheric and interocular separation. Other groups of cats were also studied for comparison, and included sham operated and normal adult cats. At adulthood, electrophysiological studies were done on these cats, in which action potentials were extracellularly recorded from single cells in the visual cortex (area 17-18 boundary) following anesthesia and paralysis. Stimulation was carried out manually and by a computer driven optical system, presenting on a tangent screen light bars at various spatial positions, orientations and directions. Receptive fields were thus mapped for all neurons and their dimensions and eccentricities were measured. The responsiveness, ocular dominance and other parameters were also studied for these cells. The results in the early deprived cats and in their controls, had shown a full separation between the two hemispheres, as reflected in the almost absolute ipsilateral eye responsiveness (> 97.0% cells). In comparison, in the sham operated and in the normal control cats only minor proportions of cells (13.0-18.7%) have been found as ipsilaterally and monocularly driven, showing almost full interhemispheric and interocular interaction. The main difference, however, in the results between the early monocularly deprived cats and their controls is that in the first group the two hemispheres were asymmetric concerning the amount of visual activation and in the second one they were very symmetric.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

A new hybrid mouse model for agenesis of the corpus callosum.

A three locus model of the inheritance of absent corpus callosum in mice was tested by creating F1 and F2 hybrid crosses from the strains BALB/cWah1 and 129/J which show incomplete penetrance for callosal agenesis. The model predicted that a few of the F2 hybrid mice would suffer severe reduction of the hippocampal commissure when the corpus callosum was absent, a condition that usually occurs only in the most consistently acallosal I/LnJ strain, and this prediction was confirmed. The C129F2 hybrid population expresses substantial genetic variation and an extremely wide range of defects of the corpus callosum, dorsal commissure of the fornix and hippocampal commissure. At the same time, these hybrids have exceptionally good health and reproductive performance, unlike their inbred parent strains. These characteristics make them ideal subjects for the study of brain-behaviour correlation using a noninvasive method.

Agenesis of Corpus Callosum↗
PubMed1994

Is interhemispheric transfer time related to age? A developmental study.

In simple visuomotor reaction time tasks, the difference between reaction time (RT) in the uncrossed hand/hemifield condition from RT in the crossed hand/hemifield, known as CUD (crossed-uncrossed difference), has been interpreted as reflecting interhemispheric transmission time (IHTT). Several studies in normal adults have found a CUD of a few milliseconds (3-4), while an abnormally long CUD has been reported in patients who underwent a surgical section of the corpus callosum or in congenital acallosal subjects. The corpus callosum, which is the most important structure for interhemispheric transfer of information, completes its myelination approximately by age ten. It has been hypothesized that the functional maturity of the corpus callosum coincides with the termination of the myelination cycle. No developmental study has focused on the development of IHTT, in relation to callosal maturation. The purpose of our study has been to investigate the development of interhemispheric transfer of visuomotor information in children aged seven to eleven, using a simple RT task with lateralized visual stimuli. The results indicate an age-related decrease of CUD, which we interpret as reflecting the maturation of the corpus callosum during childhood years.

Cerebral Cortex↗
PubMed1984

Agenesis of the corpus callosum in ddN strain mouse associated with unusual facial appearance (flat-face).

In the course of an experiment involving brother-sister matings between ddN strain mice, mice occurred with an unusual facial appearance (flat-face). Subsequently, 4 mice with flat-face were bred from the litters of the second birth (ca. 10% frequency). This flat-face was assumed to be the result of a malformed short nose, hypoplastic maxilla and mandible, and hypertelorism. These 4 flat-face mice exhibited no significant delays in growth, motor ability or the development of learning ability. Histologically, they were all characterized by an almost total absence of callosal fibers and the presence of abnormal longitudinal neuromatous bundles. Therefore, the flat-face mice may be useful as experimental animals for brain research, as one can easily judge that they lack the corpus callosum from the facial appearance.

Abnormalities, Multiple↗
PubMed1985

Further investigation of visual evoked potentials elicited by lateralized stimuli: effects of stimulus eccentricity and reference site.

Visual evoked potentials (VEPs) to small lateralized flashes were recorded from the parietal midline, homotopic lateral central and occipital electrodes, and from left and right mastoid processes, all referred to a balanced non-cephalic reference. Two stimulus eccentricities, 4 degrees and 10 degrees, were employed, and a comparison made between the non-cephalic and linked mastoid references. P120 (measured at lateral occipital sites only) peaked earlier and was of smaller amplitude at the electrode contralateral to the visual field of stimulus exposure. N160 peaked earlier at central than occipital sites, was larger from electrodes over the contralateral hemisphere, and at the occipital sites only, peaked earlier in the electrode contralateral to the visual field of stimulus exposure. These effects were virtually unaffected by the eccentricity manipulation and it is concluded that light scatter across the visual midline is unlikely to be responsible for the observed pattern of ipsilateral-contralateral VEP asymmetries. The mastoids were found to detect significant stimulus-locked activity in the same latency range as the occipital N160 component. However, comparison of the non-cephalic and linked mastoid references revealed only non-specific effects, and no sign of any change in the pattern of ipsilateral-contralateral VEP asymmetries, or the magnitude of the associated latency differences. It is concluded that these effects may be of value in the study of callosal transfer.

Adult↗
PubMedDate not supplied

Comparison of human transcallosal responses evoked by magnetic coil and electrical stimulation.

Human transcallosal responses (TCRs) were elicited by focal magnetic coil (MC) stimulation of homologous sites in contralateral frontal cortex and compared with those to focal anodic stimulation. With MC stimulation, the TCR consisted of an initially positive wave with an onset latency of 8.8-12.2 msec, a duration of 7-15 msec, and an amplitude which reached up to 20 microV, sometimes followed by a broad low amplitude negative wave. With anodic stimulation, a similar response was obtained in which the positive wave was similar in latency and maximum amplitude, but had a greater duration. With anodic stimulation, not only was the TCR threshold below that for contralateral movement, but it reached substantial size at intensities below motor threshold. With MC stimulation, contralateral arm movement and scalp corticomotor potentials were observed when the MC was displaced posteriorly towards the central sulcus. Unlike with anodic stimulation, the MC evoked TCR was usually not preceded by a prominent EMG potential from temporalis muscle and was not associated with subject discomfort. The TCR provides unique information concerning the functional integrity of callosal projection neurons, their axons and transsynaptic processes in recipient cortex. This information may prove useful in the evaluation of intrinsic cerebral mechanisms and in establishing cortical viability.

Corpus Callosum↗
PubMed1992

Activation of the neck muscles from the ipsi- or contralateral hemisphere during voluntary head movements in humans. A reaction-time study.

Reaction times (RTs) of EMG onset of agonist right and left sternocleidomastoid (SCM) and splenius (SPL) muscles in response to acoustic (AC) or unilateral somatosensory (SS) stimulation were measured in normal subjects, during head rotation (to the right or to the left) and flexion. No significant difference was present in the AC-RT of SCM muscles of the two sides between rotations or flexion. The same was true for the SPL. Under the tactile condition, in which the stimulus was delivered to one index finger, the RTs of both agonist muscles were shorter during head rotation toward the stimulus than away from it: the SCM contralateral to the stimulated finger was faster than the ipsilateral SCM, while the reverse was true for the SPL. During flexion, the SS-RTs of the SCM of both sides were similar, and similar in turn to the SCM-RT during rotation away from the stimulus. When the stimulus was delivered to the shoulder, the RT difference between the agonist SCMs disappeared. The delay in the activation of the SCM ipsilateral to the stimulated finger is compatible with the interhemispheric transmission time in the absence of callosal connection between the hand areas of the primary somatosensory cortex. The data favour the hypothesis that SCM activation during voluntary head rotation is controlled by the ipsilateral hemisphere.

Adult↗
PubMed1996

Foot pathology and risk factors for diabetic foot disease in elderly men.

We examined 3 groups of elderly men; men with diabetes and previous or present foot ulcers, men with diabetes, and men without diabetes. In the foot diseased group, diabetes duration was longer (18 +/- 11 vs 8 +/- 7 years), insulin treatment was more common (86% vs 7%), fasting blood glucose and HbA1c were significantly higher (10.5 +/- 4.0 mmol/1, 8.4% +/- 1.6%) than in the diabetic control group (8.3 +/- 3.4 mmol/l, 7.4 +/- 1.7%). Men in the foot diseased group were taller than men in the diabetic group and non-diabetic men (1.79 vs 1.74 m) but not more obese (BMI 26-27 kg/m2 in all three groups). Current or previous alcoholic problems were more common in the foot diseased group (32%) compared to the control diabetic group (9%) and the non-diabetic group (10%). Diabetic patients with known foot disease had more often callosities, absent hair growth, dry skin and redness, compared to the other groups. Psychosocial problems (alcohol and divorce), long standing diabetes duration and poor metabolic control seem to be of importance for the development of diabetic foot ulcers.

Aged↗
PubMedDate not supplied

Human corpus callosum in aging and Alzheimer's disease: a magnetic resonance imaging study.

The involvement of the corpus callosum in aging and Alzheimer's disease (AD) is not clear. We measured cross sectional areas of the entire corpus callosum (CC), as well as the front 20% (genu), middle 60% (body), and posterior 20% (splenium) of the structure from a midsagittal MRI slice in AD patients (N = 20), and young (N = 16) and old (N = 13) control subjects. We found that mean CC area in young controls was 570 +/- 107 mm2. Aging did not significantly affect the mean area of the CC (562 +/- 98 mm2). A small, significant reduction was seen in AD in comparison to the young control group (480 +/- 133 mm2). However, AD is accompanied by a large and statistically significant reduction in the genu area in comparison to both young and old control subjects. A trend toward an age-dependent reduction in the body area is also accentuated in AD patients who showed significantly smaller callosal bodies than young controls. We conclude that selective changes within corpus callosum accompany aging and AD pathology.

Adult↗
PubMed1990

A case of neurofibroma of the palmar cutaneous branch of the median nerve.

This case report describes a previously unreported entity, a neurofibroma of the palmar cutaneous branch of the median nerve. The lesion presented as a palmar mass with an overlying abnormality of the skin. Treatment consisted of excision of the lesion. Infiltration of the terminal branches of the nerve by the tumour prevented nerve reconstruction but provided a previously unknown diagnostic clue: fibrosis of an area of skin innervated by the involved nerve, which had the appearance of a callosity.

Adult↗
PubMed1986

Transfer of visual information after unilateral input to the brain.

Visual callosal connections are more numerous and widespread in the association areas than in the primary visual cortex and adjoining visual areas. In keeping with this, the amount of "wrong" ipsilateral visual field that is represented in the various cortical areas of primates and cats increases as one goes from primary visual cortex to extraoccipital areas. Therefore it can be argued that transfer of unilaterally presented visual stimuli occurs mainly at the temporal and parietal cortical level.

Animals↗
PubMed1992

Biological substrates of anatomic asymmetry.

Asymmetric cortical areas differ in volume and in the number of neurons. There are also differences between asymmetric and symmetric areas. As asymmetry increases, the total area of the region decreases, suggesting that when a brain is symmetric, it is the result of two large sides rather than two small sides. Also, these volume differences are caused by changes in the number of cells, not changes in cell-packing density. The ontogenetic basis for this difference in cell numbers likely relates to events that occur quite early in corticogenesis before final mitosis of proliferative units, but definitive proof is lacking. Finally, the pattern and degree of callosal connections differ between symmetric and asymmetric brains, with differential axonal pruning being implicated as the likely mechanism.

Animals↗
PubMed1996

Neuronal plasticity induced by neonatal monocular (and binocular) enucleation.

Monocular (ME) and binocular enucleation has become a useful experimental tool for analyzing the mechanisms of neural plasticity. ME when performed during an early postnatal period (up to 15 days after birth) initiates a series of adaptive reactions in the visual (and other sensory) system(s) which tend to compensate for the lost sensory capacity. Extirpation of one eye (usually the right) destroys afferents to both lateral geniculate bodies dorsal nucleus (CGLd) and superior colliculi (CS), being severely impaired by the degeneration of retino-geniculate and collicular synapses. The sprouting of retinogeniculate fibers coming from the remaining eye replaces these synapses in both CGLds. Ipsilateral representation of the remaining eye (usually of minor significance) becomes extended in the left CGLd and consequently in the left visual area, just as in the superior colliculi. A similar but somewhat smaller extension takes place in the contralateral CGLd and visual cortex. The strengthening of commissural connections results in a remarkable extension of callosally connected stripes and patches in both hemispheres. After ME in the critical period, the control over behavior is taken over by the remaining eye. Its power of resolution is improved because of the higher survival of (mainly ipsilaterally projecting) ganglion cells. Therefore, both hemispheres are still available for storing visual information. In ME rats the learning of visual tasks requires both hemispheres, but relearning is still possible after extirpation of the contralateral one. The possible two main mechanisms of adaptive plastic changes are: (i) replacement of degenerated synapses by sprouting collaterals of ingrowing foreign fibers, and (ii) neurons having morphologically intact but inactive synapses establishing connections with afferent fibers other than the usual. The same mechanism is seen operating in cross-modal adaptive reactions as well.

Animals↗
PubMed1981

Long-term facilitation of excitatory synaptic transmission in single motor cortical neurones of the cat produced by repetitive pairing of synaptic potentials and action potentials following intracellular stimulation.

The effects of postsynaptic firing activity on excitatory postsynaptic potentials (EPSPs) were studied in the motor cortex of anaesthetized cats. Postsynaptic firing was induced by 1-5 nA cathodal current pulses via the recording intracellular microelectrode, while EPSPs were elicited by thalamic, callosal, pyramidal tract and somatosensory stimuli. In 102 cells, EPSP-spike stimulus pairs were applied with 0.2-1/sec frequency and 10-100 msec interstimulus intervals. In 42 neurones, reversible facilitation of paired EPSPs appeared lasting from 4 to 47 min. The synaptic facilitation in most cases was accompanied by membrane depolarization and an increase in input resistance. The effectiveness of current induced action potentials upon test EPSPs provided evidence for the postsynaptic localization of plastic changes occurring in conditioning experiments.

Action Potentials↗
PubMed1983

Multiple sets of visual cortical neurons projecting transitorily through the corpus callosum.

In areas 17 and 18 of adult cats only a few neurons send bifurcating axons to more than one contralateral area or to areas in both hemispheres; most neurons seem to project to only one area. We now found that such a selective connectivity is already present at birth, i.e. several weeks before transitory callosal axons are eliminated. This is true even for those portions of cortex which will lose access to the corpus callosum: in particular different neurons project transitorily from medial area 17 to different contralateral areas. Thus cortical neurons may be induced to project to specific targets by a mechanism operating long before (and possibly independent of) the axon elimination. The latter may, however, be responsible for the final topographic organization of the connections.

Animals↗
PubMed1988

Morphology of identified projection neurons in layer 5 of rat visual cortex.

We studied the morphology of neurons in layer 5 of rat visual cortex (area 17) projecting to the contralateral hemisphere and the superior colliculus. Double labelling with fluorescent tracers indicated that these projections arise from different populations of cells. To reveal the morphology of the cells we stained retrogradely labelled neurons intracellularly in living brain slices. Callosal projecting pyramidal cells have 3-6 basal dendrites and an apical dendrite which never reaches higher than layer 3. Corticotectal cells have 6-8 basal dendrites and a prominent apical dendrite which always forms a large tuft in layer 1. Thus, neurons in the same cortical layer that give rise to different projections also differ in their morphology. However, each population of neurons has a rather stereotyped dendritic branching pattern, despite a large variation in soma size.

Animals↗