Biomedical subjects

P H Silver

Publications and source records attributed to P H Silver.

17 recordsLinked to original sources

PubMed1988

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↗

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 When external visual feedback was withdrawn in the performance of a bimanual tracking task, partial commissurotomy patients, in whom the anterior portions of the callosum were cut, deviated significantly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

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↗

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↗

PubMed1977

Experiments concerning the initiation of the choroid fissure in Gallus domesticus.

121 experiments are reported in Gallus domesticus, in which the left optic primordium from donor embryos ranging from stages 9 to 17 (Hamburger & Hamilton) was grafted upside down into host embryos at approximately stage 11-(12 somite stage), replacing the host right primary optic vesicle, which had previously been removed. In 36 experiments, up to donor stage 12+, the choroid fissure in the graft developed in hostwise ventral orientation, i.e. from the original dorsal quadrant of the graft. In four cases no fissure appeared. In donor stage 17 grafts, the fissure was invariably in graftwise dorsal orientation. In the intermediate donor stages 14 and 15, hostwise fissures occured in 12 out of 23 experiments, and in the donor stages 15 and 16, in 7 out of 28. Six cases were seen in which the fissure was in a position approximately midway between the hostwise and graftwise positions. Multiple fissures were not encountered. The results are compared with those reported in Trition by Sato (1933).

Animals↗

PubMed1976