Lavanya Vijayaraghavan, Jatin G. Vaidya, Clare T. Humphreys, Leigh J. Beglinger, Sergio Paradiso

This study investigated motivational changes in a 44 year-old man (PJ) who developed considerable reduction in spontaneous activity and speech, flat affect, social withdrawal, loss of interest, inability to "feel," and lack of concern regarding his medical condition after bilateral, focal, anoxic lesions of the globus pallidus. PJ and 30 male controls performed a task designed to parse hedonic evaluation, or liking, from incentive motivation, or wanting. Affective stimuli were presented on a computer screen and subjects controlled viewing time by pressing keys. PJ's liking and wanting of unpleasant stimuli was similar to that of controls. In response to pleasant stimuli, PJ showed normal ratings of wanting and hedonic appreciation, but significantly reduced viewing time or made no responses. Active withdrawal from liked stimuli could constitute the basic mechanism underlying poor motivation and social withdrawal associated with globus pallidus damage.