Tactile discrimination learning in the monkey: the effects of unilateral or bilateral removals of the second somatosensory cortex (area SII).

The tactile impairment in monkeys with unilateral removals of area SII is seen as possibly analogous to the rare condition of tactile agnosia. The lesions in a new series of animals with SII removals are described. The performance of 3 groups of monkeys is compared: no group differences were obtained on visual tasks (except retrieval of a moving target); minimal if any differences were obtained on inter-manual transfer of tactile learning; significant differences were found between animals with unilateral or bilateral removals of SII relative to unoperated animals at re-learning tactile discrimination tasks, irrespective of the hand being used. These findings suggest that area SII projects to a further neural system involved in somatosensory performance; and that a unilateral removal has its effect through the functional disruption of the intact SII.