Unilateral hemispheric injury and ipsilateral instinctive grasp reaction.

Development of pathological grasping in the hand ipsilateral to a focal cerebral lesion was studied in 100 consecutive patients with unilateral hemispheric lesions caused by recent stroke. Thirteen of 45 patients with right-hemispheric damage (29%) but only two of 55 patients with left-hemispheric damage (4%) showed pathological grasping. The ipsilateral grasping was of the nature of an instinctive grasp reaction. Lesion sites in the patients with this ipsilateral instinctive grasp reaction (IIGR) were in either the perisylvian region or the subcortical region. The IIGR was highly correlated with various right-hemispheric behavioral syndromes. These results suggest that the IIGR is another of the right-hemispheric behavioral syndromes and that the basis of this sign is a disturbance of selective attention. The preponderance of right-sided IIGR may reflect the right hemisphere's dominance for attention and the greater tendency in man to explore the right side of space.