Compensatory mechanisms--neural and behavioural: evidence from prenatal damage to the forebrain commissures.
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Agenesis of Corpus Callosum↗
Biomedical subjects
M A Jeeves
Publications and source records attributed to M A Jeeves.
Hemispheric interactions: the bilateral advantage and task difficulty.
Twenty-five normal subjects made "same-different" responses to dot patterns presented in the LVF, RVF or bilaterally. Task difficulty was manipulated in each condition by varying the number of dots in the two patterns presented from two to four to six. The pairs of patterns always had the same number of dots on a given trial. Response latency and accuracy worsened as the number of dots increased for all three presentation conditions and for both "same" and "different" judgements. Overall, responding was faster and the number of errors lower on Bilateral presentations. For response latencies to identical patterns of dots, the size of the bilateral advantage increased relative to RVF responding as task difficulty increased but did not change significantly relative to LVF responding. When the two patterns were not identical the size of the advantage did not change as task difficulty increased. "Same" judgements were faster but less accurate than "different" judgements. A model of hemispheric interactions is proposed to account for the findings.
Adult↗
Stereo perception in callosal agenesis and partial callosotomy.
Stereoperception in two acallosal patients and two partial callosotomy patients was compared with that of three normal subjects. All three patients with the splenium missing, whether due to agenesis or surgical intervention, showed midline deficits and broadly similar profiles; namely, they made few uncrossed midline responses. The patient with partial callosal section but with the splenium almost totally spared performed better at the midline than in the periphery. All degrees of disconnection produced some overall loss of performance, confirming the results of Hamilton and Vermeire (In Two Hemispheres--One Brain, F. Lepore, M. Pitto and H. H. Jasper (Editors), pp. 315-333. Alan R. Liss Inc., New York, 1986) and Hamilton et al. (Suppl. Invest. Ophthal. Vis. Sci. 28, 294, 1987). The results are discussed in the context of earlier reports of human and animal studies of stereoperception. Bearing in mind reports of structural alterations in layer III of the striate cortex in acallosals (Shoumjra, K. et al. Brain Res. 93, 241-252, 1975. Also, Akert, K. et al. Trans. Am. Neurol. Assoc. 79, 151-153, 1954), it is speculated that the specific difficulties encountered by them in handling uncrossed disparities may be due to a marked reduction or absence of far neurones in acallosal brains (Poggio, G. F. and Poggio, T. Ann. Rev. Neurosci. 7, 379-412, 1984). The likely importance of the anterior commissure in the efficient integration of crossed disparity (near neurones) (Cowey, A. In Brain Mechanisms and Spatial Vision, D. Ingle (Editor), NATO Advanced Study Institute Series, Martinus Nijhoff, The Hague, 1985) is seen as a possible explanation of the acallosals relative success in making crossed disparity judgements. The variability of performance in normals documented by Hamilton and Vermeire (In Two Hemispheres--One Brain, F. Lepore, M. Pitto and H. H. Jasper (Editors), pp. 315-333. Alan R. Liss Inc., New York, 1986) and Hamilton et al. (Suppl. Invest. Ophthal. Vis. Sci. 28, 294, 1987) is, not surprisingly, even more marked amongst acallosals.
Adult↗
Reading in callosal agenesis.
It has been suggested that deficits in explicit phonological processing are causal in developmental dyslexia. Deficits in such skills have been reported in developmental phonological dyslexia, though not in developmental surface dyslexia. The reading performance of two children with callosal agenesis, who have been previously shown to have impairments on rhyming tasks, are reported. Neither child is dyslexic in the traditional sense, since word reading levels are appropriate for age. However, both children have impaired development of the phonological reading route despite normal lexical skills. The pattern of their reading is therefore comparable to developmental phonological dyslexia. Problems in explicit phonological processing may be causal in the failure to establish an efficient phonological reading route but this is insufficient to create difficulty with word recognition itself. The corpus callosum may be essential for the normal development of a phonological reading route.
Agenesis of Corpus Callosum↗
Ten pen men: rhyming skills in two children with callosal agenesis.
Cases of callosal agenesis provide unique opportunities to investigate the normal role of the corpus callosum in the development of cognitive functions, including language. The only language impairment which has been consistently observed in three acallosal patients is on the retrieval of words from rhyming cues. Two new cases of callosal agenesis in children of normal intelligence are presented. Their performance on a variety of rhyming tasks involving both production and recognition of rhyme is reported. Both children display deficits and possible explanations are discussed.
Adolescent↗
The formation of finger grip during prehension in an acallosal patient.
The grasping behaviour of an acallosal patient is compared with that of a group of normals. Video records of the hands of the patient and the normals allowed frame by frame analysis of the prehensile movements involved. The normals behaved according to the earlier reports by Jeannerod [Behav. Brain Res. 19, 99-116, 1986; and in Two Hemispheres--One Brain, F. Leporé, M. Ptito and H. H. Jasper (Editors), pp. 369-383, Alan R. Liss, Inc., New York, 1986] with the thumb and forefinger closing upon the object to be grasped by the time it was reached. By contrast the acallosal did not begin to close the finger and thumb until after contact was made with the object. The results are seen as further evidence for (a) the enhanced development of uncrossed ipsilateral pathways in acallosals and (b) absence in acallosals of the normal inhibitory action of the callosum in suppressing such enhanced ipsilateral output which consequently competes with the contralateral output controlling the fingers.
Adult↗
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↗
Cerebral asymmetries and interhemispheric processes.
Those who attempt to characterize the functions of the cerebral hemispheres tend, broadly speaking, to do so either in terms of structural specializations or of different information-processing modes. Often little attention is paid to the possible importance, in determining the outcome of experiments in this field, of interhemispheric processes. An experiment is described which concurrently studies hemispheric response differences and interhemispheric processes. Sets of dot patterns are learned, each made up of an original and three distortions of the original. The degree of distortion is systematically changed and is quantified in terms of information theory. Subjects then examine pairs of patterns and decide whether they belong to the 'same' family, i.e. an original and one of its distortions, or 'different', i.e. a pattern previously learned and a completely new one. Manual response times are recorded for 'same' and 'different' responses and functions plotted of response latencies against degree of pattern distortion. The pairs of patterns are presented under three different conditions. Either both patterns in one visual field (unilateral condition), one pattern in each visual field (bilateral condition) or the patterns one above the other straddling the vertical meridian (central condition). Response latencies are shortest for the bilateral condition, next shortest for the unilateral condition and slowest for the central condition. Models which may account for these results are examined and one crucially involving changed information transmission rates with increasing distortion of patterns to be compared is found to provide the most parsimonious explanation of the results from all three experimental conditions.
Adolescent↗
Interhemispheric transfer of spatial tactile information in callosal agenesis and partial commissurotomy.
The De Renzi Rod Test was used to investigate the transfer of spatial tactile information between hands in acallosals and partial commissurotomy patients. The right-handed performance of young acallosals was impaired, confirming the results of an earlier study by Meerwaldt (1983). The adult acallosals, with one exception, showed no difference between right and left hand performances. Two partial callosotomy patients with sparing of the most caudal parts of the body of the callosum showed no difference between the hands. A third callosotomy patient with little, if any, sparing of the most caudal part of the body of the callosum showed a marked impairment when performing the tactile task with the right hand. The unimpaired performances of the adult acallosals are attributed to the use of ipsilateral pathways and the development of behavioural strategies. The callosotomy patients' results are consistent with the mapping by Pandya and Seltzer (1986) of the interhemispheric callosal pathways between the cortical parietal areas in non-human primates.
Adult↗
A further study of language function in callosal agenesis.
A subset of the tests of language ability administered by M. Dennis (1981, Brain and Language, 12, 33-53) was given to two adult acallosal patients. One of the patients studied showed widespread language deficits not restricted to the syntactic-pragmatic core as in Dennis' patient. The other showed a very specific deficit which does not encompass syntactic-pragmatic skills. The data does not support the view that the corpus callosum is necessary for the normal development of specific language functions.
Adolescent↗
The Chief Scientist reports...theoretical problems and practical solutions to behaviour disorders in retarded people.
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Adult↗
Visual cells in the temporal cortex sensitive to face view and gaze direction.
The direction of eye gaze and orientation of the face towards or away from another are important social signals for man and for macaque monkey. We have studied the effects of these signals in a region of the macaque temporal cortex where cells have been found to be responsive to the sight of faces. Of cells selectively responsive to the sight of the face or head but not to other objects (182 cells) 63% were sensitive to the orientation of the head. Different views of the head (full face, profile, back or top of the head, face rotated by 45 degrees up to the ceiling or down to the floor) maximally activated different classes of cell. All classes of cell, however, remained active as the preferred view was rotated isomorphically or was changed in size or distance. Isomorphic rotation by 90-180 degrees increased cell response latencies by 10-60 ms. Sensitivity to gaze direction was found for 64% of the cells tested that were tuned to head orientation. Eighteen cells most responsive to the full face preferred eye contact, while 18 cells tuned to the profile face preferred averted gaze. Sensitivity to gaze was thus compatible with, but could be independent of, sensitivity to head orientation. Results suggest that the recognition of one type of object may proceed via the independent high level analysis of several restricted views of the object (viewer-centred descriptions).
Animals↗
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↗
Visual analysis of body movements by neurones in the temporal cortex of the macaque monkey: a preliminary report.
Movement provides biologically important information about the nature (and intent) of animate objects. We have studied cells in the superior temporal sulcus of the macaque monkey which seem to process such visual information. We found that the majority of cells in this brain region were selective for type of movement and for stimulus form, most cells responding only to particular movements of the body or some part of it. A variety of cell types emerged, including cells sensitive to: translation of bodies in view, movements into view (appearance) or out of view (disappearance) and the articulation and rotation of the body/head. Directional selectivity for cells sensitive to translation tended to lie along one of 3 orthogonal Cartesian axes centred on the monkey (towards/away, left/right and up/down). One type of rotation sensitive cell was tuned to rotation about one or more of these axes, a second type was sensitive to different head rotations which brought the face to confront the monkey or turned the face away. Reconstructions of cell positions indicated that cells of the same type were clumped anatomically both across the surface of the cortex and perpendicular to the surface.
Animals↗
Functional consequences of the transcallosal removal of intraventricular tumours.
Colloid cysts and other benign tumours of the third and lateral ventricles may be exposed through a small incision in the body of the corpus callosum. This approach is practicable even when ventricular dilatation is slight, and is theoretically less likely to cause epilepsy than the more usual transcortical approach. Disturbances of memory have been noted soon after such operations, but do not cause serious long-term disability. Three patients who underwent transcallosal removal of cysts or tumours some years earlier have been tested by procedures designed to demonstrate interhemispheric transfer of information: they were all found to have defects in transfer of tactile data, but not of information obtained visually. They were not aware of this inability, and do not appear to be inconvenienced by it. The transcallosal route is convenient. The operation sacrifices a functionally significant part of the corpus callosum, but the neurological sequelae have seemed acceptable. However, especially in the elderly, stereoventriculoscopic aspiration may be considered as the initial method of treatment.
Adolescent↗
A developmental study of hemisphere specialization for recognition of faces in normal subjects.
In a developmental study of hemisphere lateralization for recognition of faces in normal subjects three groups of subjects (mean ages: 7 years 9 months; 13 years 10 months; and 19 years 6 months) were tested. The procedure was a go-no go reaction time task in which the subject responded to faces tachistoscopically presented to the right or left visual field. A left visual field superiority was found for the two older age groups, which is interpreted as a right hemisphere dominance for recognition of faces. However, the 7 and 8 year old group did not demonstrate a significant visual field difference. These results indicate that the hemisphere specialization (lateralization) for recognition of faces involves processes which develop with increasing age through childhood and is not well-established until some time after the age of 8 and before age 13.
Adolescent↗
A developmental study of hemisphere specialization for alphabetical stimuli.
Three groups of normal female subjects (7 and 8 years of age, 13 and 14 years of age, and young adults) were tested on a choice reaction time task using a tachistoscopic presentation of single letters to either hemisphere. The two older groups of subjects were found to exhibit a significant right visual field (left hemisphere) superiority in reaction time to letters, but the 7 and 8 year old children did not show a hemisphere asymmetry. These reaction time results for the two older groups are consistent with Rizzolatti et al.'s (1971) finding of a right visual field superiority in reaction time to letters in male adults. The analyses of error rates for visual field differences were not significant for the children or the adolescents. In this study, in contrast to Rizzolatti et al.'s result with male adults, the female adults produced a significant visual field difference in error rate.
Adolescent↗
Further studies of tactile perception and motor coordination in agenesis of the corpus callosum.
A 12-year-old female with total agenesis of the corpus callosum has been tested on several tasks involving tactile perception and motor coordination. Her performance has been compared with a group of normals of the same age and sex and a group of subjects matched for age, sex and I.Q. On 3 of the bimanual motor coordination tasks the acallosal's performance was not clearly distinguishable from the control's. She was, however, slower than the controls on the pegboard task. On a transfer of training task (formboard) the acallosal was slower than normals and did not manifest transfer. However, transfer of training was shown on a maze-learning task. No deficit was found in the ability to tactually cross-identify objects, but a deficit in tactile cross-localization was evidenced.
Adolescent↗