At which steps of spatial working memory processing do striatofrontal circuits intervene in humans?

Striatofrontal circuits have been implicated in spatial working memory in n on-human and human primates. To determine at which steps of information pro cessing (stimulus encoding, storage or response programming) they intervene , we compared 32 levodopa-treated patients with idiopathic Parkinson's dise ase (PD) and 32 matched control subjects in a visuo-spatial pattern span pa radigm. Our testing procedure allowed us to evaluate the influence of: (1) the type of encoding (controlled vs free); (2) the nature of interference d uring a 10 s delay (spatial vs verbal), and (3) response elaboration (repro duction vs error detection). As expected, the performance of control subjec ts was significantly better in controlled than in free encoding, in verbal than in spatial interference and in detection than in reproduction, clearly demonstrating the sensitivity of the procedure to these factors. Compared to controls, PD patients were impaired in all conditions and the severity o f the deficit was significantly correlated with that observed in tests of e xecutive functions. The global pattern of performance, however, was identic al to that of controls. These data confirm the involvement of striatofronta l circuits in spatial working memory in humans and suggest that the executi ve working memory component intervenes at all steps of working memory proce ssing. (C) 1998 Elsevier Science Ltd. All rights reserved.