Delayed-response performance following optic tract section, unilateral frontal lesion, and commissurotomy.

Abstract

Serial operations were performed on 9 Macaca mulatta to transect optic tract on one side, to ablate one frontal area, and to transect the corpus callosum, psalterium and anterior commissure. Delayed-response performance in Ss with visual input ipsilateral to normal frontal area was superior to that in those with visual input contralateral to normal cortex. Subsequent commissurotomy virtually ended correct delayed-response performance in Ss with contralateral lesions, but had far less effect on those with ipsilateral lesions. Hyperactivity was not correlated with impairment of delayed-response performance. Corticocortical connections between occipital and anterior frontal cortex via cortical association fibers are probably crucial for successful delayed-response performance. Moreover, interhemispheric connections are capable of sustaining psychological functions dependent on corticocortical connections.

Visuospatial asymmetries and interocular transfer in the split-brain rat.

“…Larger heading errors and entries into more nontarget quadrants make clear that callosum section resulted in an impairment in (a) orientation toward the target and (b) formation and maintenance of a spatial representation of the target in relation to the cues signifying its location and to changing spatial position. These findings add a specific spatial impairment to earlier reports of learning deficits in brain-bisected cats and monkeys (Glickstein, Aurora, & Sperry, 1963; Robinson & Voneida, 1970), debilities variously described as the result of interrupting the “mass action” facilitation of the corpus callosum (Jeeves, 1981) or of “halving the neuron pool” (Butler, 1981). Whatever the basis for this split-brain cognitive impairment, it is clear that in mapping the spatial surround, two halves of a divided brain do not add up to the capability of a whole one.…”

Active Representation of Shape and Spatial Location in Man

“…Following initial visual processing in the occipital cortex, it has been proposed that the processing of spatial and non-spatial features of objects follow divergent dorsal and ventral pathways to the posterior parietal and the inferior temporal cortex, respectively (Van Essen, 1985;Zeki and Shipp, 1988). Lesions within these pathways impair performance on both discrimination and delay tasks in the respective modality (Glickstein et aL, 1963;Fuster et aL, 1985;Quintana et aL, 1989). Recently, relatively selective activation in the parietal and temporal cortex associated with attention to spatial and non-spatial attributes has been demonstrated in man using positron emission tomography (PET) (Corbetta et aL, 1991;Haxby^ai, 1991).…”