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PubMed1988

The development of callosal and corticocortical innervation in the neocortex of the hamster.

The development of cortical afferentation by callosal and ipsilateral corticocortical fibers was studied in hamsters by transport of wheat germ agglutinin conjugated to horseradish peroxidase. Elongation of callosal axons (and possibly also of corticocortical fibers) started a couple of days before birth and extended through the first postnatal days. After a "waiting" period of a few days, axons were seen innervating restricted target sectors of the cortex. The zones of origin of these projections were initially exuberant, but they were subsequently trimmed down to overlap with the corresponding terminal fields.

Afferent Pathways↗
PubMed1987

Callosal projections in the visual cortex and the vertical meridian of the visual field in the albino rat.

Studies using electrophysiological and HRP-labeling techniques showed that the lateral border of physiologically determined primary visual cortex coincides with the cytoarchiectonically defined area 17/18a border. The dense callosal projections are distributed in a zone, about 1.5 mm wide, along this border, which lies in the callosal zone, about 1/4-1/3 of the zone width from its lateral limit. There are two representations of the vertical meridian of the visual field, one in the proper of area 17, about 1/3 of the zone width from its medial limit, the other in area 18a, at about the lateral zone limit.

Animals↗
PubMed1987

Distribution of visual callosal projection neurons in the siamese cat: an HRP study.

In this experiment we studied the distribution of callosal cells in various visual cortical areas of both common and siamese cats using the HRP method. The results showed that the most notable difference between the two strains concerned the primary visual areas. Indeed, labeling in areas 17 and 18 was significantly lower in siamese cats and only a few scattered cells were encountered at the 17/18 border. In general, the number of callosal cells forming interhemispheric connections within areas 17, 18 and the 17/18 border was dramatically reduced in the siamese. For all other visual areas (19, lateral suprasylvian subdivisions, 20 a, b and 21 a, b) the distribution was comparable for both species. A study of the laminar distribution indicated that, for common and siamese cats, medium and large pyramidal cells were mainly concentrated in layers III and IV whereas in deeper layers we found a mixture of small pyramidal and fusiform neurons.

Animals↗
PubMedDate not supplied

MRI of callosal disconnection due to cerebral infarction.

Magnetic resonance imaging (MRI) was performed to study two cases of callosal disconnection due to cerebral infarction. Both cases had pure alexia and right homonymous hemianopsia. Midsagittal inversion recovery (IR) images demonstrated that the corpus callosum was completely intact, and coronal IR images revealed involvement of the lingual gyrus, fusiform gyrus, forceps major, inferior longitudinal fascicle, and optic radiation in the dominant cerebral hemisphere in both cases. Midline sagittal images provided direct visualization of the corpus callosum but did not provide sufficient information for the study of callosal disconnection syndromes. Coronal reconstructions aided in visualizing the relationship of lesions to the adjacent structures of cerebral white and gray matter. MRI may be one of the most useful tools for understanding the process of interhemispheric transference of information.

Aged↗
PubMedDate not supplied

Sonographic appearance of callosal agenesis: correlation with radiologic and pathologic findings.

Sonographic features are described in six infants in whom total or partial agenesis of the corpus callosum was confirmed by either computed tomographic or pathologic examination. The six patients demonstrated a range of abnormalities involving the neuraxis as well as other systems, notably cardiovascular, gastrointestinal, and genitourinary. Chromosomal abnormalities were present in two patients. The sonographic features of callosal agenesis seen in these patients included: lack of characteristic acoustic interfaces to define the corpus callosum on both coronal and sagittal sonograms; increased separation and parallelism of the bodies of the lateral ventricles; loss of the characteristic convexity of the medial border of the anterior horns of the lateral ventricles; variable prominence of the occipital horns of the lateral ventricles; variable degree of superior extension of the third ventricle; alteration or absence of the cavum septi pellucidi; and radial arrangement of cerebral sulci about the prominent third ventricle. Cases of partial agenesis may show the dysplastic features found in complete agenesis. However, only some of the callosal echoes are present. The sonographic features of partial agenesis in one infant had not been described before.

Agenesis of Corpus Callosum↗
PubMed1985

[Characteristics of monosynaptic connections between neurons of the callosal system and specific thalamic nuclei].

In the sensorimotor cortex of awake rabbits monosynaptic afferent and efferent connections of callosal neurons (CN) with ipsilateral specific thalamic nuclei (ventral posterolateral, ventral posteromedial, ventral lateral and anteroventral nuclei) were analyzed by electrophysiological method and compared with those of target-units of callosal fibres (TU). It was demonstrated that CN and TU differed in their monosynaptic inputs from the thalamus and in their axons projecting to these structures and/or being a part of the pyramidal tract. These differences were the following: a greater portion of TU had the descending projections (54%) as compared with CN (14%); 22% of TU responded by monosynaptic action potentials to the stimulation of specific thalamic nuclei, while CN never manifested such responses. TU could project to the thalamus through the main axon stem as well as through the collaterals of the pyramidal tract axons. It is supposed that the discovered differences evidence for the much greater convergence of the thalamic relay neuron effect on TU, thus revealing the mechanism underlying the differences both in receptive field properties and in the background and evoked activity of CN and neurons synaptically excited in response to the transcallosal stimulation.

Animals↗
PubMed1979

[Interaction of callosal and extracallosal systems].

Studies of the topography of homotopic transcommissural evoked potentials in 85 symmetrical points of the cat motor cortex, prior to and after section of the corpus callosum, revealed the functional areas as follows: acommissural (53% of the total area), purely callosal (23%), mixed (22%), and purely extracallosal (2%). The summation and reciprocal interrelationships between the callosal and extracion flows spreading over the extracallosal system.

Animals↗
PubMed1979

Callosal transfer and left-hand anomia in schizophrenia.

The theory of callosal failure in schizophrenia is examined using the test for left-hand anomia. It is argued that if the corpus callosum is affected in schizophrenia with consequent difficulty of transmission between the two sides of the brain, a greater number of left-hand errors should be found in producing the names of objects held by that hand because the speech area of the left hemisphere is no longer available for the description of the perceptions of the left hand. The findings support this view and they confirm the communication failures of the brain related to callosal disturbance.

Adult↗
PubMed1984

Callosal syndrome: implications for understanding the neuropsychology of stroke.

A case is presented of callosal syndrome following cerebral hemorrhage and amphetamine abuse in a 26-year-old right-handed man. There were few hemispheric findings but a full callosal syndrome including left apraxia to verbal commands, left tactile anomia, left agraphia, right constructional apraxia, failure of blindfolded side-to-side hand replication and form-board testing showing loss of interhemispheric transmission including intermanual interference. The "draw-a-clock" test showed left inattention when drawn with the right hand but not the left, and perseveration was noted for spatial tasks done with the right hand and symbolic tasks done with the left. The patient recovered functionally almost completely but testing demonstrated continued loss of interhemispheric transmission. The case is considered of most interest for its potential in explaining phenomena observed in severe unilateral hemispheric lesions. Our findings suggest that perseveration is not a dysfunction of the damaged portion of the brain, but a phenomenon associated with intact brain attempting unfamiliar tasks. The persistence of left hemi-inattention is attributed to the inability of the left hemisphere to utilize spatial information to compensate for the phenomenon of inattention. Left-sided dyskinesia following left hemisphere lesions was attributed to the lack of symbolic information necessary to perform some movements. Dysprosody was attributed to lack of tonal information to the left hemisphere. Recovery of function following severe unilateral lesions may be largely due to compensatory learning by the intact hemisphere and assertion of ipsilateral control. As our patient originally assumed an inverted left-handed writing posture, we assume the posture is controlled by the right hemisphere.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

[Callosal connections in the cat parietal cortex during postnatal ontogenesis].

By means of the method based on the retrograde axonal transport of horseradish peroxidase topography, quantitative and qualitative composition of homotopic neurons in the cat cerebral parietal associative cortex performing callosal connections have been studied. When comparing the data of the experiment with those previously obtained on distribution of the axonal terminals in the comissural neurons, certain places are revealed where concentration of the homotopic callosal connections of the parietal cortex field 7 take place. A morphological characteristic of the longaxonal pyramidal and stellate neurons forming these connections is presented.

Afferent Pathways↗
PubMed1984

[Right hemiasomatognosia and sensation of amputation caused by left subcortical lesion. Role of callosal disconnection].

A 72-year-old right-handed hypertensive man presented with a right brachial monoplegia, and hypesthesia of the right half of the body to touch and pricking, sparing the face. A CT scan 2 weeks later showed a spontaneous hyperdense area corresponding to a left subcortical parietal hematoma. The patient used his spontaneous language to express body image disturbances: intense prolonged feeling of amputation related to the upper limb and foot on the right side, hemiasomatognosia without anosognosia, autotopagnosia. Also associated were a right-sided visual negligence and a more general inability to handle spatial data leading to a temporospatial disorientation. Mild language disorders were suggestive of subcortical aphasia: normal incitation and repetition; with semantic paraphasias, poor verbal fluency. Furthermore comprehension of orders or propositions concerning spatial data were poor. Finally, there were signs suggestive of callosal disconnection: paradoxical extinction of the left ear during dichotic listening, agraphia and anomia of the left hand, ideomotor apraxia of the left upper limb, difficulty in visual transfer. The lesion interrupted thalamic tracts to parietal regions and callosal fibers linking parieto-occipital association areas. This twofold lesion was analyzed for each of the neuropsychological disturbances observed. Certain aspect of cerebral function in this patient were reminiscent of "split-brain" disorders. The left hemisphere which "speaks" fails to understand the feelings of the right hemisphere: unfamiliarity of places, sensations of illness, resulting in an unadapted speech. The pathophysiology of feeling of amputation is discussed.

Aged↗
PubMed1984

[Callosal connections of the somatosensory area in the primate: anatomical and electrophysiological studies].

In order to study the callosal connections of the hand sensory field of the second somatosensory area of the monkey, experiments were carried out by combining the method of retrograde neuronal tracing with microelectrode recording. In six monkeys, Macaca Irus, single or multiple (5-8) injections of horseradish peroxidase (HRP) were performed into the cortex of the parietal operculum of one side. Neurones retrogradely labelled with HRP (callosal neurones) were found in the post-central gyrus and in the parietal operculum of the contralateral hemisphere. Microelectrode recording from this hemisphere showed that the cortical zones of both the first and the second somatosensory area containing neurones excited by sensory stimulation of the contralateral hand also contained HRP-positive neurones.

Animals↗
PubMed1980

Neonatal enucleation induces an asymmetric pattern of visual callosal connections in hamsters.

Autoradiography and the horseradish peroxidase (HRP) technique were used to investigate visual callosal connections in normal hamsters and in animals which had one eye removed at birth. In normals and in the cortex contralateral to the remaining eye in the neonatal enucleates, callosal cells and terminal labeling were restricted to the region around the area 17-18a border. In the cortex ipsilateral to the remaining eye in the neonatal enucleates labeled cells and terminal labeling were observed throughout areas 17 and 18a.

Animals↗
PubMed1993

The role of callosal section in surgical treatment of epilepsies.

Using current microsurgical technique, the procedures of both partial and complete corpus callosum section may be performed with minimal morbidity and with full assurance of completeness of callosal fiber division. Between 65% and 80% of patients have had significant improvement in terms of generalized seizure control. These results are similar to those observed at a number of other epilepsy centers now performing this surgery, and the benefit is long lasting. The neuropsychologic effects of callosal division have now been fairly well characterized. Although demonstrable in all patients, these rarely have been problematic and in nearly all instances have been outweighed by the benefit in terms of seizure control.

Corpus Callosum↗
PubMed1977

Can callosal speed of transmission be inferred from verbal reaction times?

Filbey and Gazzaniga (1969) found that verbal reaction times were shorter to right than to left visual field stimuli. They interpreted this reaction time difference (30 to 40 msec) to reflect callosal transmission time, i.e., the delay required for information received in the right hemisphere to be acted upon by the verbal left hemisphere. We have performed four verbal reaction time experiments with normal subjects, utilizing differing hemifield stimulus presentations and task requirements. Stimuli were: small lights (light-emitting diodes); checkerboard pattern briefly flashed; small circles; consonant-vowel-consonant triads, either meaningful or nonsense. Contrary to Filbey and Gazzaniga's observations, we found no difference between verbal reaction times to left and right half-field presentations, or a significantly shorter reaction time with left-field presentations, depending upon experimental conditions. Faster reaction times with left-field stimuli were found in left-handed as well as right-handed subjects. Our data indicate that it may be premature to infer callosal speed of transmission from verbal reaction times to half-field stimuli. The paradoxical finding of faster verbal reactions to right hemisphere visual inputs does not appear to be related to handedness, and it occurs with meaningful stimuli; this finding remains unexplained.

Corpus Callosum↗
PubMedDate not supplied

[Identification and properties of callosal neurons of the sensomotor region of the rabbit cerebral cortex].

Antidromic unit responses to the stimulation of the homotopic area of the contralateral hemisphere were specified in the cortical sensorimotor area of the unanaesthetized rabbit. The response latencies and their variability, the maximal reproduced stimulation frequencies, stability of the response, presence of certain contesting relationships between the background activity and the tested action potentials are as a whole reliable criteria for identifying extracellularly recorded callosal neurons. The criteria of certain relationships between the background and evoked action potentials allowed to disclose callosal neurons with slow conduction.

Action Potentials↗
PubMed1997

Interhemispheric transfer of visual information in humans: the role of different callosal channels.

We have assessed the interhemispheric transmission time (IHTT) by electrophysiological means in normal subjects performing a visuomotor reaction time task. We subtracted the latency of ERP components (P1 and N1) evoked by lateralized visual stimuli presented to the ipsilateral hemifield (indirect-callosal pathway) from the latency of the same components evoked by stimulation of the contralateral hemifield (direct pathway). Estimates of IHTT ranged between 5.77 msec and 12.54 depending upon the type of component and the location of the electrode sites. More anterior locations yielded shorter values of IHTT, and overall IHTT tended to be 7 msec shorter for the N1 component than for the P1 component. Moreover, there was an asymmetric IHTT for N1 in central sites with shorter latencies in the direction right-to-left hemisphere than in the opposite direction. Taken together, these results are in keeping with the idea that interhemispheric transfer of visuomotor information does not occur at the level of the primary visual areas but at more anterior cortical areas. The shorter IHTT for the N1 component suggests the involvement of the callosal connections between the inferotemporal areas of the two hemispheres.

Adult↗
PubMed1997

A callosal disconnection syndrome of vascular origin.

OBJECTIVE: To study the after-effects of a selective lesion of the corpus callosum on the capacity in transferring spatial information on arm posture derived from kinesthesia and vision. DESIGN: Neuropsychological and psychophysical evaluations of a patient with callosal damage. SETTING: Institute of Neurology, University of "Tor Vergata", Rome, Italy and Research Centre, IRCCS "S. Lucia", Rome, Italy. PATIENT: P.V., a 59 years old man suffering from a vascular lesion of the left half of corpus callosum and left callosal radiations. MEASURES: Sensori-motor and cognitive tasks. Exo- and egocentric pointing abilities tasks. RESULTS: Impairments due to a disconnection between the two cerebral hemispheres were pointed out. About pointing abilities, errors were greater when each hand pointed to the remembered location of the other hand. Errors decreased dramatically with eyes open for right hand pointing to remembered location of left and right hand, and left hand pointing to remembered location of left hand. Open eyes left hand pointing to remembered location of right hand remained as poor as with eyes closed. CONCLUSIONS: The results appear compatible with the following network: visual information from striate and extrastriate cortex is passed forward to parietal cortex bilaterally (even in PV due to the splenium sparing). Kinesthetic information from parietal cortex of left and right hemisphere converge on a single visuokinesthetic center, lateralized to the left hemisphere. Information about limb position in three-dimensional space is then encoded in body-centered coordinates and passed forward to motor and premotor cortex in the frontal lobe. These frontal regions are those disconnected in PV.

Brain Ischemia↗