Altered event processing in persons with Parkinson's disease

Electrophysiological alterations during action semantic processing in Parkinson's disease

Assessments of action semantics consistently reveal markers of Parkinson's disease (PD). However, neurophysiological signatures of the domain remain under-examined in this population, especially under conditions that allow patients to process stimuli without stringent time constraints. Here we assessed event-related potentials and time-frequency modulations in healthy individuals (HPs) and PD patients during a delayed-response semantic judgment task involving related and unrelated action-picture pairs. Both groups had shorter response times for related than for unrelated trials, but they exhibited discrepant electrophysiological patterns. HPs presented significantly greater N400 amplitudes as well as theta enhancement and mu desynchronization for unrelated relative to related trials. Conversely, N400 and theta modulations were abolished in the patients, who further exhibited a contralateralized cluster in the mu range. None of these patterns were associated with the participants' cognitive status. Our results suggest that PD involves multidimensional neurophysiological disruptions during action-concept processing, even under task conditions that elicit canonical behavioral effects. New constraints thus emerge for translational neurocognitive models of the disease.

Aberrant neural processing of event boundaries in persons with Parkinson's disease

The perception of everyday events implies the segmentation into discrete sub-events (i.e. event segmentation). This process is relevant for the prediction of upcoming events and for the recall of recent activities. It is thought to involve dopaminergic networks which are strongly compromised in Parkinson's disease (PD). Indeed, deficits of event segmentation have been previously shown in PD, but underlying neuronal mechanisms remain unknown. We therefore investigated 22 persons with PD and 22 age-matched healthy controls, who performed an event segmentation task with simultaneous electroencephalography (EEG). Both groups had to indicate by button press the beginning of sub-events within three movies showing persons performing everyday activities. The segmentation performance of persons with PD deviated significantly from that of controls. Neurophysiologically, persons with PD expressed reduced theta (4-7 Hz) activity around identified event boundaries compared to healthy controls. Together, these results point to disturbed event processing in PD. According to functions attributed to EEG activities in particular frequency ranges, the PD-related theta reduction could reflect impaired matching of perceptual input with stored event representations and decreased updating processes of event information in working memory and, thus, event boundary identification.

Relation between event segmentation and memory dysfunction in Parkinson's disease

The perception of everyday events is thought to imply the segmentation into discrete sub-events. Involvement of dopaminergic networks in this process could relate to particular problems of persons with Parkinson's disease (PD) to recall recent activities. In an event segmentation task, persons with PD and healthy controls had to indicate the beginning of sub-events within three movies showing persons performing everyday activities. In a subsequent recognition task, they should judge whether presented pictures of sub-events were part of the watched movies. In a final order memory task, they had to arrange pictures in the sequence in which they had occurred. With respect to the overall segmentation behavior, persons with PD diverged from healthy controls only in the most familiar of the three demonstrated everyday activities. Moreover, persons with PD compared to healthy controls showed generally worse event recognition and committed more errors in the order memory task. These memory deficits were the higher, the more the segmentation moved away from the 'normative' segmentation pattern identified in healthy controls. The findings suggest that dysfunctional structuring of sensory event information contributes to deficient event representations of ongoing everyday activities and recall problems of these recently perceived events in persons with PD.