Contextual processing deficits in Parkinson's disease: the role of the frontostriatal system

We investigated the role of the frontostriatal system in contextual processing, by examining neural correlates of local contextual processing in Parkinson's disease (PD). Local context was defined as the occurrence of a short predictive series of visual stimuli occurring before delivery of a target event.

EEG was recorded in eight PD patients and eight controls. Recording blocks consisted of targets preceded by randomized sequences of standards and by sequences including a predictive sequence signaling the occurrence of a subsequent target event. Subjects pressed a button in response to targets. Peak P3b amplitude and latency were evaluated for targets after predictive and non-predictive sequences.

Behavioral and electrophysiological measures showed that controls processed predicted and random targets differentially, while PD patients processed these similarly. Reaction times were shorter for predictable than for random targets in controls but not in patients. PD patients failed to generate the expected P3b latency shift between predicted and random targets, which is observed in controls.

These findings show that predictive local context effects on target detection are altered in PD patients.

The findings suggest a key role for the frontostriatal system in contextual processing.