“…PD is characterized by death of midbrain dopamine cells projecting to the BG (Kish et al, 1988), and associated motor symptoms including tremor, rigidity, and slowness of movement (McAuley, 2003). PD patients also have a variety of cognitive deficits, ranging from procedural learning to working memory, decision making and attention (Ashby, Noble, Ell, Filoteo, & Waldron, 2003;Cools, Barker, Sahakian, & Robbins, 2001bFrank, 2005a;Frank, Seeberger, & O'Reilly, 2004;Gotham, Brown, & Marsden, 1988;Jackson, Jackson, Harrison, Henderson, & Kennard, 1995;Knowlton, Mangels, & Squire, 1996;Maddox & Filoteo, 2001;Rogers et al, 1998;Shohamy et al, 2005). Given the proposed BG role in selecting among various competing low-level motor responses by modulating frontal motor activity, and the parallel circuits linking the BG with more frontal cognitive areas (Alexander et al, 1986;Middleton & Strick, 2000, 2002, it is natural to extend this action selection functionality to include higher-level cognitive decisions (Frank, 2005a;Frank & Claus, 2006;Frank et al, 2001;Houk, 2005).…”