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PubMed1979

The effect of the sequence of contralateral cortical and collicular lesions on the rate of relearning a visual discrimination by cats.

Visual field deficits which follow ablation of the posterior two-thirds of one cerebral hemisphere in the cat have been shown to be ameliorated by ablation of the contralateral superior colliculus. The present study was designed to determine whether the sequence in which contralateral cortical and collicular lesions are made is a significant factor affecting the rate of monocular relearning through the eye ipsilateral to the cortical lesion. Nine adult cats had the optic chiasm sectioned, were trained to criterion monocularly on a dark-light discrimination, and were divided into two groups. Four cats (Group S) had one superior colliculus ablated, followed one month later by ablation of the contralateral two-thirds of the neocortex. Five cats (Group C) had the same lesions in the reverse order. One month after the second brain lesion, each cat was retrained monocularly through each eye on the dark-light discrimination for food reward in a Y-maze. Through the eye ipsilateral to the cortical lesion, all cats in Group S relearned to criterion more rapidly than cats previously reported with only unilateral neocortical lesions. Four of the five cats in Group C were severely retarded in relearning and two of these cats failed to relearn. The results show that when chiasm-sectioned cats are trained monocularly in a Y-maze on a dark-light discrimination, ablation of the superior colliculus prior to ablation of the contralateral neocortex facilitates relearning through the eye ipsilateral to the cortical ablation. When ablation of the superior colliculus follows the neocortical lesion, learning occurs but is not facilitated by the additional lesion.

Animals↗
PubMed1997

Sodium amobarbital memory tests: what do they predict?

Severe transient postoperative memory deficits among epilepsy patients with resection from one temporal lobe may be indicative of increased risk for amnesia had more extensive removal of mesial structures occurred. Immediate postoperative testing may provide some validation for risk of amnesia as predicted by the intracarotid sodium amobarbital memory test (IAP-M). Thirty patients (24 not considered at risk for amnesia and 5 who failed the IAP-M) were tested on the first, second, and third days following resection from the right or left temporal lobe. Results suggest that the IAP-M paradigm used does not necessarily predict postoperative memory performance.

Amnesia↗
PubMed1992

A review of cognitive outcome after hemidecortication in humans.

This review of the effects of hemidecortication in humans has been limited to studies of cognitive outcome published during the last 20 years. More directly than in the case of split-brain patients, the patients reviewed here attest to the remarkable ability of a single hemisphere, whether left or right, to support at least at modest levels a wide range of cognitive functions--from visual perception, through memory and intellectual processes, to language and even speech. In some cases, as has been indicated, the surgical removal of a diseased hemisphere has resulted in improvement of cognitive function. This positive outcome has occurred more frequently in patients with early (i.e. congenital or perinatal) onset of seizure disorders than in those with late onset (e.g. Rasmussen's disease). But even for the latter patients, the cognitive costs of the surgery per se have rarely been severe. And in both types of case, the incidence of either complete or substantial postoperative relief from intractable seizures has been high, ranging around 80-90%. Although the therapeutic efficacy and small cognitive costs of the surgery are now quite well established, little is known yet regarding the specific cognitive defects that arise from the loss of one as opposed to the other cerebral hemisphere. Intelligence levels have been found to be equally low, averaging in the mid-60s and almost never rising above 100 in patients with either left or right hemidecortications, and memory quotients have most often appeared to fall in line with the IQ scores, again without clear evidence of any difference in the effects of left and right removals. Even in the case of visual spatial perception, considered to be a hallmark of right hemisphere function, the evidence is unclear, one study reporting selective impairment on difficult visuospatial tasks in right hemispherectomised patients, but another not. Only in regard to language processes is there a consensus regarding the differential effects of left and right hemidecortication, and here the differences are apparent only in the relatively subtler aspects of language. Thus, the isolated right hemisphere is at a significant disadvantage compared with the left in the comprehension of abstract, low frequency words, in phonetic feature analysis, and in the subtleties of grammar, such as the comprehension of passive negative constructions and the correct use of morphological markers in unfamiliar contexts (e.g. application of comparative and superlative forms of an adjective to nonwords.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Damage, Chronic↗
PubMed1987

Hemidecortication selectively alters release of glutamate in perfusates collected from cerebral cortex of unrestrained rats.

The effect of hemidecortication on the in vivo release of amino acids was examined in different areas of the cerebral cortex of the freely-moving rat. After one side of the cortex was lesioned by aspiration, four guide tubes for push-pull perfusion were implanted chronically on the contralateral side so as to rest above the frontal, parietal, temporal and occipital areas of the cortex. After 10-14 days elapsed, each of these regions was perfused with an artificial cerebrospinal fluid (CSF) at a rate of 25.0 microliter/min. Two types of assays were undertaken to determine the release of either newly synthesized amino acids from [14C]glucose precursor or the actual endogenous content in samples of perfusate. The separation of the [14C]amino acids was performed by thin layer chromatography, whereas endogenous amino acids were separated by HPLC with electrochemical detection and quantitated in the range of 1.0-10.0 picomoles. When compared to the control group, samples collected in the hemidecorticate rat showed no significant differences in the new synthesis of glutamate, aspartate, glutamine, glycine, and GABA from the precursor. On the other hand, the analysis of the endogenous amino acid neurotransmitters revealed that the levels of glutamic acid and glutamine declined in samples obtained from the parietal and frontal cortex, respectively. These results implicate further the potential role of glutamic acid as a neurotransmitter of interhemispheric connections in the cerebral cortex.

Animals↗
PubMed1985

Performance of complex arm movements and facial-movement sequences after cerebral commissurotomy.

Two patients with presumed complete midline section of the interhemispheric commissures and two patients with partial section were asked to copy complex arm movements and facial-movement sequences. Their performance was compared with our previously published findings on these tasks for patients with unilateral removals from the frontal, temporal or parietal region. On the arm-movement task, the commissurotomized patients were impaired equally with either the left or right arm and were as poor at performing this task as patients with excisions of left parietal cortex. On the face-movement task, commissurotomized patients performed very poorly, scoring significantly lower than all excision groups. There was no significant difference on either task between the performance of the patients with partial and those with complete sections.

Adult↗
PubMed1994

Sound localization in hemispherectomized patients.

In order to precisely evaluate the consequences of cortical damage on free-field sound localization in humans, the present study examined response accuracy to auditory targets in three hemispherectomized patients and IQ-matched controls. Listeners reported sound location by pointing with their dominant hand to the apparent sound location in an anechoic chamber. Two conditions were tested: (i) localization of a fixed-sound source and (ii) localization of the beginning and the end of a simulated moving stimulus. In both conditions, the responses of the patients were less accurate than those of the controls in the hemifield contralateral to their removed hemisphere. Moreover, the single-case analyses revealed that the performances obtained with fixed sources were generally more precise than those obtained with moving sources. This result is discussed in terms of a differential involvement of cortical and subcortical pathways in the processing of stationary and moving sounds. Finally, the age at surgery and the post-surgical interval were related with the magnitude of the deficits, suggesting the possible influences of functional reorganization and cerebral plasticity.

Adolescent↗
PubMed1988

Recovery from early cortical damage in rats. IV. Effects of hemidecortication at 1, 5 or 10 days of age on cerebral anatomy and behavior.

Rats with complete removal of the neocortex of one hemisphere in adulthood (hemidecorticate) were compared behaviorally and anatomically with rats with similar removals at 1, 5, or 10 days of age. There was an unexpected relationship between cortical thickness in adulthood and age at surgery: the earlier the lesion the thicker the cortex. At the two extremes rats hemidecorticated in adulthood had a reduction of up to 10% in the contralateral hemisphere, rats with hemidecortications on the day of birth had cortex that was thicker than adult operates. Behaviorally, the animals were administered several tests including a spatial navigation task, tests of beam walking and swimming, tests of turning bias, and a measure of claw cutting. The main finding was that although the hemidecortication at all ages produced a reliable behavioral change on all measures, the neonatal hemidecorticates performed better than the adults. Further, the earlier the lesion, the better the animals performed. These results are contrasted with the effects of bilateral frontal or parietal neocortical removals in infancy where the earliest lesions have the most severe effect on cortical thickness and behavior. This comparison shows that unilaterality of brain damage is an important factor in predicting recovery or sparing of function from early lesions.

Animals↗
PubMed1998

Anterior temporal lobectomy, hippocampal sclerosis, and memory: recent neuropsychological findings.

Anterior temporal lobectomy (ATL) is an effective and increasingly utilized treatment for nonlesional, intractable mesial temporal lobe epilepsy. However, this surgery results in domain-specific neuropsychological morbidity for a subset of patients. Within the past decade, multidisciplinary studies have revealed that left ATL patients without significant sclerosis in the resected hippocampus are most at risk for a substantial postacute decline in the ability to encode new verbal information. These patients are also at risk for a significant decrement in confrontation naming and other retrieval-based language abilities. The memory deficit is not attributable to this disruption of language. A relationship between hippocampal sclerosis (HS) status and memory performance has not been identified consistently in right ATL patients, but investigation of new visuospatial measures continues. The influence of variables other than HS on neuropsychological outcome is also discussed.

Anomia↗
PubMed1998

Neuropsychological outcome following anterior temporal lobectomy in patients with and without the syndrome of mesial temporal lobe epilepsy.

The nature, pattern, and degree of neuropsychological change following anterior temporal lobectomy (ATL) were examined as a function of the presence or absence of the syndrome of mesial temporal lobe epilepsy (MTLE). Fifty-four patients exhibited the syndrome of MTLE, while 34 patients were without the syndrome (non-MTLE). The test-retest performance of a group of 40 epilepsy patients who did not undergo surgery was used to derive regression-based estimates of test-retest change. Overall, the MTLE group did not show significant cognitive decline following ATL. In contrast, the left non-MTLE group showed significant declines on verbal memory, confrontation naming, and verbal conceptual ability. Further, verbal memory was the most substantial area of decline, and was independent of seizure outcome. Clinical and theoretical implications of these findings are discussed.

Adult↗