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PubMed1993

Language and development in FG syndrome with callosal agenesis.

The FG syndrome is characterized by unusual facies, sudden infant death, developmental delay, and abnormalities of the cardiac, gastrointestinal, and central nervous systems. No longitudinal data on development in surviving patients are currently available. Serial evaluations of a patient with FG syndrome, whose sole central nervous system anomaly was agenesis of the corpus callosum, showed a consistent pattern over time. Specific language impairments in syntactic and pragmatic-semantic areas are emerging. These findings represent the first detailed data on which expectations for children with the FG syndrome can be based. The findings also fit theoretical constructs on the function of the corpus callosum and may therefore be generalized to provide expectations for other patients with isolated agenesis of the corpus callosum. Given the information gained from this case, it is clear that language intervention/consultation should be a pivotal service for such children, and that the speech-language pathologist should play a role in the development of an integrated educational services plan.

Abnormalities, Multiple↗
PubMed1982

Simple reaction times to lateralized visual stimuli in a case of callosal agenesis.

Simple reaction times (RTs) of a young acallosal woman were measured using three different intensity levels of the visual stimulus. It was found that "'crossed" stimulus/hand combinations yielded finger RTs about 20 msec longer, on average, than "uncrossed" combinations. In addition, an inverse relation was found between stimulus intensity and the magnitude of this crossed/uncrossed difference in RT. It was also found that vocal RTs displayed a large advantage (18 msec) for right visual-field stimulation. It is suggested that the stimulus information in crossed finger reactions must cross the midline through visually-coded neurones in the acallosal brain.

Adult↗
PubMed1985

Reaction times to lateralized visual stimuli in callosal agenesis: stimulus and response factors.

A young acallosal man was intensively tested in a standard simple reaction time (RT) paradigm using briefly-presented lateralized spots for light. In Experiment 1, findings on previous acallosal patients of a large disadvantage for crossed (e.g. right hemifield-left hand) as against uncrossed (e.g. left hemifield-left hand) RTs were replicated. This crossed-uncrossed difference (CUD), as in previous work, turned out to be smaller in a bimanual response task than in the conventional unimanual task. Experiment 2 was a factorial study of unimanual RTs in which (a) stimulus intensity and (b) spatial S-R compatibility, were varied. As in a previously tested patient, decreased intensity resulted in a greatly increased CUD. S-R compatibility on the other hand had no effect on CUD. The results are interpreted as favouring a role for visual commissural neurones in the acallosal CUD, and as evidence against a spatial compatibility hypothesis.

Adult↗
PubMed1986

Neglect in a patient with partial callosal disconnection.

A right-handed woman suffered destruction of the anterior two thirds of the corpus callosum and the adjacent medial frontal lobes as a sequel of bleeding from an anterior cerebral artery aneurysm. When drawing and writing with her right hand, the patient displayed neglect of the left hemispace. In line bisection each hand deviated towards the side ipsilateral to the lesion, but the size of error decreased when the lines were placed to the ipsilateral side of the body. When tested for her verbal report of tachistoscopically presented, horizontal pairs of simple geometrical figures, she showed a systematic rightward shift of attention when stimuli were presented to the left hemispace or to the centre, but not with presentation to the right hemispace. These results cannot be attributed to a mere deficit in motor control of the hand, nor can they be entirely referred to perceptual rivalry between simultaneous bilateral stimuli. It seems that a directional bias in favour of the right side is introduced when the left hemisphere processes sensory information to prepare a motor or verbal response.

Agnosia↗
PubMed1986

Hemispheric specialization and attention: effects of complete and partial callosal section and hemispherectomy on dichotic monitoring.

Dichotic word monitoring tasks were given to four cases with complete forebrain comissurotomy, three cases of partial section of the corpus callosum, one case of right hemispherectomy, and control subjects. The task involved a unimanual response to target words in either ear (divided attention, Experiment 1) or to target words in one voice that changed ears unpredictably (focused attention, Experiment 2). Left-ear extinction, defined as chance level (25%) detection of left-ear targets and 75% right-ear target detection, varied both between and within subjects during divided attention. No examples of extinction were obtained with focused attention. These results highlight attentional aspects of dichotic listening. Neither the structural, hemispheric asymmetry model (Cortex 3, 163-178, 1967), nor the cognitive, attention priming model (Attention and Performance V, pp. 87-97, Academic Press, New York) could account for the obtained results. We propose an alternative account in terms of the different processing modes and attentional capabilities of the two cerebral hemispheres.

Adolescent↗
PubMed1987

Visual processes in a hemialexic patient with posterior callosal section.

A patient with surgical section of the splenium and, probably, the posterior end of the truncus of the corpus callosum was studied 9-13 yr after the operation. His reading aloud, reading comprehension and word-matching abilities were moderately disturbed only in the left hemifield. These three disturbances were equally disturbed. The disturbances were not the result of visual disturbances such as tachistoscopic hemiamblyopia or tachistoscopic hemineglect since Landolt's ring matching was intact in the left hemifield as well as in the right. The disturbances were also not due to the disturbance of tachistoscopic word perception since the patient correctly performed same-different judgment of pairs of words in each hemifield. In his reading aloud and reading comprehension disturbances, ideogram words were less impaired than phonogram words, even when the number of letters in the words was the same. His picture naming ability was not disturbed in each hemifield.

Adult↗
PubMed1987

Perceptual and attentional processes following callosal section in humans.

Studies are reviewed that examine how perceptual and attentional systems operate in the cortically disconnected human. The data indicate that even though both simple and complex perceptual information associated with the cognitive activities of each disconnected half brain show virtually no interactions, the attentional system remains largely integrated in the split-brain patient. It also appears that the human brain is subject to a set of finite resources it can allocate to cognitive activities. These resources are not changed following cortical disconnection. Taken together, studies to date support the view that the attentional system is an independently functioning and integrated entity, following brain bisection, that participates in both perceptual and cognitive activities of each hemisphere.

Attention↗
PubMed1988

Bimanual co-ordination in callosal agenesis and partial commissurotomy.

Studies [Preilowski, B.F.B. in Cerebral Localization, pp. 116-131, Springer, Berlin, 1975; Reynolds, D.M. and Jeeves, M.A. Neuropsychologia 12, 287-290, 1974] of bilateral motor coordination in commissurotomy patients pointed to the importance of direct interhemispheric integration for the fine regulation of the lower motor system within each hemisphere. When external visual feedback was withdrawn in the performance of a bimanual tracking task, partial commissurotomy patients, in whom the anterior portions of the callosum were cut, deviated significantly when drawing lines which required asymmetrical input from the two hands. The task devised by Preilowski was given to two adult acallosals, an 11 yr old acallosal boy, and an 11 yr old girl in whom the centre one-third of the corpus callosum had been sectioned. The acallosals performed in a manner similar to Preilowski's partial commissurotomy patients. The results were interpreted as confirming the interhemispheric integrative function of the corpus callosum. It is argued that they constitute further evidence for the existence of hemispheric dominance for motor control in acallosals. The partial commissurotomy patient did not differ in performance from normals. Her results were consistent with the view that it is the anterior parts of the callosum which are crucial for the interhemispheric integration of the lower motor system in each hemisphere.

Adult↗
PubMed1988

Tactual extinction without anomia: evidence of attentional factors in a patient with a partial callosal disconnection.

Tactual extinction was examined in a 43-yr-old left-handed male patient (MM) with a hematoma in the trunk of the corpus callosum sparing the genu and the ventral part of the splenium as well as the cerebral hemispheres. Experiments I and II showed no deficit in tactual perception nor in the inter-hemispheric transfer of tactual information. In Experiment III, MM palpated stimuli differing in their association value, and responded vocally or manually. There was no difference in performance between the hands in unimanual control conditions, but in a dichhaptic condition an overall right-hand advantage was observed, depending on the kind of stimulus and on the mode of response: such results were not observed in control subjects. Results showed that MM's left-hand performance reached right-hand levels after specific modifications in the allocation of attention between the hands or the load of information in haptic memory (Experiment IV). Experiment V revealed a major deficit in the matching of left- and right-hand information only for the dichhaptic procedure. The results are discussed with a view of cerebral mechanisms as dynamic rather than structurally determined: it is suggested that extinction phenomena are sensitive to cognitive strategies and attentional factors and that the corpus callosum plays a critical role in the lateral control of attention to tactual as well as to auditory and visual information.

Adult↗
PubMed1995

Transient left-sided alien hand with callosal and unilateral fronto-mesial damage: a case study.

A patient who showed a transient left alien hand after a subarachnoid haemorrhage, due to a ruptured aneurysm of the anterior communicating artery, is described. No left agraphia and left apraxia could be found. A CT-scan including coronal sections showed a right medial frontal hypodensity and different ischaemic lesions in the anterior part of the corpus callosum. The possible anatomic site of the lesion responsible for the permanent form of alien hand is discussed.

Adult↗