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PubMed1989

Negative evidence of difference between right- and left-handers in interhemispheric transfer of information.

The present study has been designed to investigate the relationship between handedness and callosal function. Based on the previous finding of a greater anatomical connection between the hemispheres in left-handers than in right-handers and in order to test the possibility of greater functional communication, the efficiency of interhemispheric transfer of information has been measured using a finger localization task. Comparison of two groups of male right-handed and left-handed subjects shows no difference in the efficiency of interhemispheric transfer of information.

Adult↗
PubMed1989

Double disconnection effects resulting from infiltrating tumors.

Patients with left hemisphere lesions deep in parietal or parietal-occipital regions close to the lateral ventricles have been reported to have impaired performance on left ear speech stimuli in dichotic listening tests. This loss has been termed "paradoxical" because it presents at the ear ipsilateral to the lesion. Two patients with infiltrating tumors which involved the corpus callosum demonstrated that effect, but also demonstrated right ear extinction on a complex-pitch discrimination test that required right hemisphere processing. Since the side at which the impairment will be demonstrated depends upon the type of test used, the term "paradoxical extinction" does not clearly describe this phenomena. It is suggested that the so-called paradoxical loss is better referred to as callosal extinction.

Adolescent↗
PubMed1991

Stereopsis in the cat: behavioral demonstration and underlying mechanisms.

The neural substrates subserving stereopsis were investigated behaviorally and electrophysiologically in the cat. In one set of studies, we examined behaviorally the ability of normal cats to perceive depth on the sole basis of spatial disparity using random-dot stereograms. Results showed that the animals were able to carry out this discrimination. We then evaluated the contribution of the optic chiasm, the corpus callosum and the primary visual cortex to this function. Results indicated that: (1) chiasma transection drastically reduced the ability of the animals to solve the random-dot problem; (2) a callosal split had little or no effect on their ability to relearn the same discrimination; (3) a section of both the corpus callosum and optic chiasm abolished this ability; and (4) bilateral lesions of areas 17-18 also abolished it. In another set of studies, we examined electrophysiologically the properties of neurons in the various visual cortical areas where disparity-based depth discrimination processes are presumed to take place. We recorded from areas 17, 18 and 19 of normal and split-chiasm cats. Results showed that: (1) the primary visual cortex of the normal cat contained cells sensitive to stimulus disparity; (2) these disparity sensitive neurons were also present in area 19 although in a much lower proportion and were more widely tuned than those in areas 17-18; and (3) following the section of the optic chiasm, there was a significant decrease in the number of disparity sensitive cells in areas 17-18, whereas in area 19 they were nearly completely absent. The results obtained from the lesion studies and from the single unit recording experiments indicate that stereoscopic depth perception is highly dependent in the cat upon the integrity of the through-the-chiasm geniculo-striate pathway and its target primary visual cortex.

Animals↗
PubMed1991

Left out axons make men right: a hypothesis for the origin of handedness and functional asymmetry.

The origin and underlying mechanisms of hand preference are still unresolved, despite extensive research and discussion. Numerous possibilities have been considered, including genetic and hormonal factors, brain insult and learning. We suggest here that naturally occurring loss of axons of the corpus callosum (either symmetric or asymmetric, with or without neuron death) may be one mechanism underlying the embryological development of hand preference and hemispheric anatomical and functional asymmetries in males. We note supporting evidence for this hypothesis from a report of increased prevalence of left-handedness in children born prematurely at the gestational age prior to the likely onset of axon loss. The practical implications of this hypothesis for clinical management in neonatal intensive care units are discussed. It is suggested that the course of loss of callosal axons may have a genetic component which is associated with a sex-related influence and which is modifiable by prenatal and early postnatal events.

Axons↗
PubMed1992

Letter matching in the hemispheres: speed-accuracy trade-offs.

Eight subjects performed physical and nominal letter-matching tasks for pairs of letters presented in the left, right, or central visual fields, using a unimanual two-choice response-time paradigm. Latencies were manipulated by using a cued response procedure, and speed-sensitivity and speed-bias functions were calculated separately for each of the peripheral visual field by response hand conditions. Hemispheric contributions to these tasks were investigated by looking for evidence of exclusive specialization and callosal transfer. The results suggest that both hemispheres are able to perform the tasks and that they do so using similar processing strategies, but they differ in the response-choice stage of the nominal identity task.

Adult↗
PubMed1993

Bilateral visual field processing and evoked potential interhemispheric transmission time.

The relationship between the efficiency of interhemispheric interactions via the corpus callosum and the speed and accuracy in making comparisons of information simultaneously presented to the right and left visual fields was studied by comparing bilateral (vs unilateral) advantages in matching letters, with evoked potential measures of interhemispheric transmission time (EP-IHTT). The primary finding was a strong correlation suggesting that larger bilateral field advantages in reaction time are associated with faster EP-IHTT. However, the association between EP-IHTT and bilateral advantage was strong only for transmission speed from left hemisphere to right hemisphere, but not for speed of transmission in the opposite direction. The data are consistent with a hypothesis of asymmetric homologue enhancement, i.e. a directionally asymmetric callosal influence which facilitates processing of letter stimuli in the right hemisphere allowing for increased response speed and accuracy of bilateral visual field comparisons.

Adolescent↗
PubMed1995

Performance on motor tasks as an indication of increased behavioral asymmetry with advancing age.

Age-related asymmetrical functional decline was tested on a sample of 64 right-handed volunteers between 60 and 64 years of age who were free from neurological illnesses and physical handicaps. Increase in functional asymmetry was explored by examining performance indexes for each hand and superiority of the dominant hand on motor tasks of different complexities: the Finger Tapping Test, the Grooved Pegboard Test, and the Pin Test. Our study revealed an increase in superiority of the right hand with age on a highly demanding task (Pin Test). This finding is discussed in light of the hypothesis of a decline in callosal functioning with age and the alternative hypothesis of a greater vulnerability of the right hemisphere in the elderly.

Aged↗
PubMed1995

Increased corpus callosum size in musicians.

Using in-vivo magnetic resonance morphometry it was investigated whether the midsagittal area of the corpus callosum (CC) would differ between 30 professional musicians and 30 age-, sex- and handedness-matched controls. Our analyses revealed that the anterior half of the CC was significantly larger in musicians. This difference was due to the larger anterior CC in the subgroup of musicians who had begun musical training before the age of 7. Since anatomic studies have provided evidence for a positive correlation between midsagittal callosal size and the number of fibers crossing through the CC, these data indicate a difference in interhemispheric communication and possibly in hemispheric (a)symmetry of sensorimotor areas. Our results are also compatible with plastic changes of components of the CC during a maturation period within the first decade of human life, similar to those observed in animal studies.

Adult↗
PubMed1983

The role of crossed and uncrossed optic pathways mediating black-white discrimination in rats with one eye enucleated at birth.

It has been reported that rats with one eye enucleated at birth (OEB) are able to relearn a black-white discrimination task originally learned with both the visual cortices intact faster than rats monocularly enucleated at three months of age (OET) when relearning is made after the visual cortex contralateral to the remaining eye is destroyed. Two experiments examined the hypothesis that functional enhancement of uncrossed optic pathways produced by monocular enucleation at birth might be the sole factor to produce such a phenomenon. The results showed that faster relearning in OEBs could not be totally explained by the hypothesis, and suggest that only when (1) there is a learning effect in the visual cortex ipsilateral to the remaining eye produced by interaction of visual information through the callosal fibers with an increased amount of information through uncrossed optic pathways during original learning and (2) relearning is mediated by enhanced functioning of uncrossed optic pathways, would such phenomenon be produced.

Animals↗
PubMed1991

Corpus callosum: multiple parameter measurements in rodents and humans.

A magnified drawing of a human or a rodent corpus callosum is traced on a digitizing tablet. From this tracing the computer calculates callosal area, perimeter, length, and 99 widths, one for each percentile location along the longitudinal axis of the callosum. In addition, the human program encloses the callosum within a rectangle to obtain several other measures. The use of percentile widths allows one to generate a callosum profile to compare different clinical groups or different species. The human callosum program is compared to one recently reported by another research group.

Algorithms↗
PubMed1989

Global stereopsis in human albinos.

The presence of global stereopsis was examined in 18 clinically diagnosed albinos; four non-albino controls were also tested including two observers with congenital nystagmus. Stereopsis was evaluated with standard clinical stereo tests and with TV generated random dot stereograms. The latter test involved electrophysiological measures of vertical eye movement tracking in response to a stimulus target. For either test procedure, global stereopsis could be demonstrated in a significant number of albinos across varying phenotypes. These results are of interest in view of electrophysiological investigations in albino animal models which indicate a paucity of binocularly driven cortical neurons in visual areas 17, 18 and 19. While stereopsis may be mediated in our albinos via residual appropriately projecting retino-geniculo-cortical fibres, we suggest that inter and intra cortical communication via corpus callosal connections may play a primary role in providing the adequate neural substrate for albino binocularity.

Adolescent↗
PubMedDate not supplied

Studies of human myelin proteins during old age.

The electrophoretic protein patterns of myelin isolated from frontal and callosal white matter were studied in adult man up to the age of 90 years. The proportions of the four major myelin proteins remained virtually unchanged as did the total protein content of white matter and of purified myelin. The total mass of purified myelin that could be recovered from white matter gradually decreased with age, suggesting an age-related loss of myelin sheath and probably neurons as well, without detectable alterations of the regular protein composition of myelin. In most cases basic protein of myelin was preceded by one or two minor protein components on electrophoresis. One of them is tentatively identified as "prebasic" protein similar to the one previously observed in other species, because of its close electrophoretic apposition to the main basic protein. The second component was found less frequently and was thought to arise from specific types of proteolysis of myelin proteins. Prolonged time intervals between death and autopsy had little, if any, effect on the proportions of basic protein and proteolipid protein. Similar results were obtained when bovine brain was incubated under conditions designed to simulate post-mortem autolysis. It was there fore concluded that meaningful data on proteins of human central myelin may be obtained even though an autopsy was not performed within a few hours of death.

Adolescent↗
PubMed1988

Interhemispheric epithelial cyst. Case report.

We report a rare case of a 54-year-old woman with an interhemispheric epithelial cyst. This will be the first report of an interhemispheric epithelial cyst without callosal agenesis. A partial excision of the cyst wall has led to her recovery with no evidence of recurrence. Ultrastructural studies suggest that the cyst was derived from the primitive neuroepithelium. We discuss the pathogenesis of the interhemispheric epithelial cyst.

Brain Diseases↗
PubMed1995

Intracerebral hematoma in patients with ruptured cerebral aneurysms.

BACKGROUND: Intracerebral hematoma from ruptured aneurysms is one of the unfavorable factors for outcome in patients with subarachnoid hemorrhage. In this study, the clinical characteristics of intracerebral hematoma in patients with ruptured aneurysms were examined. METHODS: The subjects were 512 patients who had been admitted by day 3 after aneurysmal rupture without episodes of rebleeding before the initial computed tomography (CT) scan. They were divided into two groups according to the findings of initial CT; groups 1 and 2 comprised patients with and without intracerebral hematoma, respectively. RESULTS: Of the 512 patients, intracerebral hematoma was observed in 98 (19%). The incidence of intracerebral hematoma was higher in patients with distal anterior cerebral and middle cerebral artery aneurysms, compared with those at other sites (both, p < 0.01). Interhemispheric, callosal, and temporal lobe/sylvian hematomas were observed more frequently in patients with anterior communicating, distal anterior cerebral, and middle cerebral artery aneurysms, respectively, than in those with aneurysms at other sites. The incidence of rebleeding was 22% in group 1 and 14% in group 2 (p < 0.05). Clinical grades on admission were higher and outcome at 6 months after onset was less favorable in group 1 than in group 2 (both, p < 0.01). The larger the intracerebral hematoma, the higher was the clinical grade and the less favorable the outcome. However, when comparing management and surgical outcome under the same clinical grades, there was no significant difference between the two groups. CONCLUSIONS: There was a close correlation between the site of hematoma and that of the ruptured aneurysm. Poor outcome in patients with intracerebral hematoma seems to be related to severity of clinical grade on admission.

Adult↗
PubMed1996

Surgical options in the treatment of interhemispheric arachnoid cysts.

BACKGROUND: Arachnoid cysts located within the interhemispheric fissure are a matter of discussion as to the surgical indication and the choice of the most appropriate surgical procedure. In fact, in spite of the large dimensions that they can reach, the clinical manifestations may remain subtle and apparently stable over the years. On the other hand, the larger utilization of prenatal ultrasound investigations has increased the number of lesions detected before they can provoke clinical manifestations. As far as surgery is concerned, two main options are available-an extrathecal shunting procedure or a direct approach to the lesion, with excision of its wall. METHODS: In this report, we analyze the results obtained in 25 children harboring an interhemispheric arachnoid cyst, surgically treated in the period 1978 to 1994. Mean age at diagnosis was 18.8 months (10 days to 15 years). RESULTS The main clinical manifestations included macrocrania, mild to moderate signs of increased intracranial pressure, cranial bulging, developmental delay, and neurologic signs. In 14 cases, the diagnosis had been obtained prenatally. The cyst was located in one hemicranium in 16 cases, whereas it was on the midline, with bilateral extension, in the remaining 9 cases; in the latter cases, variable degrees of callosal agenesis were also observed. All 25 children were operated on. In 16 of them, the treatment consisted of a craniotomy with wide excision of the cyst lining and marsupialization into the subarachnoid spaces of the midline (and/or into the ventricular system). In 6 children, the surgical procedure was a cystoperitoneal (CP) shunt. The last 3 children of our series underwent craniotomy and cyst excision after having been treated by means of a ventriculoperitoneal shunt. At follow-up examination, 17 children are normal, and the remaining 8 disclose mild to moderate psychomotor retardation. CONCLUSIONS: Although both craniotomy and CP shunt are associated with good results, the first surgical procedure offers the advantage of avoiding the insertion of a permanent cerebrospinal fluid shunt device and the known complications of this type of procedure.

Adolescent↗
PubMed1984

Profiles of right hemisphere language and speech following brain bisection.

A variety of language tasks were administered to two patients who had undergone staged callosal section in an effort to control otherwise intractable epilepsy. Right hemisphere lexical capacity varied and preliminary results suggest that the case displaying greater semantic power also possessed some syntactic competence. This same case (V.P.) was also capable of expressive language from the right hemisphere. This rare capacity allowed for fresh observations on the dynamic interactions of conscious control that occur in this kind of patient.

Adult↗
PubMed1988

Neural mechanisms underlying stuttering: evidence from bimanual handwriting performance.

Left- and right-handed male and female stutterers were compared with fluent speakers on a bimanual handwriting task. On each trial four words were read to the subject. After repeating the words, subjects had to write the initial letters as quickly as possible using the two hands simultaneously and without visual guidance. As a group, stutterers were slower, made more mirror-reversed letters, and formed letters of poorer quality than fluent speakers. The effects were the same for males and females, and the data for left- and right-handers were mirror-symmetric with respect to left and right hands. Evidence was found for two subgroups of stutterers with respect to scores on the dependent variables. It was suggested that the overall pattern of results implicates the supplementary motor area in the mediation of stuttering, possibly through relatively ungated callosal pathways.

Adult↗
PubMed1989

Sentence comprehension following agenesis of the corpus callosum.

The sentence comprehension skills of a 6-year-old girl with callosal agenesis were compared to skills of three other children matched for age and verbal IQ. Sentence-picture matching and acting out tasks were used with reversible active, passive, and center-embedded relative clause sentences. The acallosal subject showed a deficit in syntactic comprehension. The difficulty was due to a failure to assign correct semantic roles to some sentence forms, not to a lack of ability to discriminate among the sentence forms. The data are consistent with a previous report by M. Dennis (1977, In Topics in child neurology, pp. 189-212) that in acallosal subjects syntactic comprehension can be adversely affected. Because this acallosal subject is only 6 years old, follow-up studies will be needed to determine whether she eventually acquires normal syntactic skills.

Agenesis of Corpus Callosum↗