Semantic and affective priming as a function of stimulation of the subthalamic nucleus in Parkinson's disease

Lexical-semantic and emotional processing deficits have been associated with Parkinson's disease. This study investigated automatic and controlled lexical-semantic processing, the automatic activation of emotional evaluations, and the processing of words conveying negative and neutral emotional connotations in a combined affective and semantic priming paradigm. Eighteen participants with Parkinson's disease who had undergone surgery for deep brain stimulation (DBS) of the subthalamic nucleus (STN) completed a lexical decision task at short and long stimulus onset asynchronies (SOAs), during on and off stimulation conditions. Nineteen non-neurologically impaired participants acted as controls. The results indicated that automatic lexical-semantic and emotional evaluative processes are unimpaired in Parkinson's disease as reflected in the presence of comparable semantic and affective priming effects at the short SOA in on and off stimulation conditions compared with healthy controls. In contrast, participants with Parkinson's disease in the off stimulation condition showed a pattern of aberrant controlled lexical-semantic processing as evidenced by a lack of semantic priming effects at the long SOA condition. Controlled semantic priming was present, however, when the participants with Parkinson's disease were receiving stimulation of the STN, suggesting that STN stimulation modulates basal ganglia-thalamocortical circuits involved in such processes. Finally, delayed reaction times for negatively valenced targets compared with neutrally valenced targets was evident in participants with Parkinson's disease in the on stimulation condition and control participants, but not for participants with Parkinson's disease in the off stimulation condition, suggesting that the incidental evaluation of negatively versus neutrally valenced words in Parkinson's disease is modulated by basal ganglia-thalamocortical circuits.