Receptive field characteristics of single units in tree shrew temporal cortex before and after lesions in areas 17 and 18
The lateral geniculate nucleus of the tree shrew projects exclusively to its striate cortex; area 18 and portions of the temporal cortex receive visual input by way of the superior colliculus and pulvinar nucleus. In contrast to striate cortex, whose cells consist of the simple and complex varieties found in other species, cells in the temporal cortex of the tree shrew were very unresponsive to visual stimulation. The majority of microelectrode penetrations in this area yielded no visual driven cells. Cells which did respond to visual stimulation usually had large receptive fields and could be driven by a variety of stimuli. Because evoked potentials are readily generated in response to light flashes in this area, a more responsive cell population had been anticipated. Possibly the trigger features of the cells of tree shrew temporal cortex are more complex than those of the striate cortex. Complete ablations of area 17 and parts of area 18 did not alter the properties either of evoked potentials or of cell responses over a survival period ranging from 2 to 6 weeks. Specifically, no orientation selective cells could be found, yet ablated animals retained visual function (cf: Snyder and Diamond, Brain Beh. Evol. 1:244, 1968). Tree shrews seem to be able to distinguish simple visual patterns after losing orientation selective cortical cells.
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