Altered alpha and theta oscillations correlate with sequential working memory in Parkinson’s disease

Daily activities like preparing a meal rely on the ability to arrange thoughts and actions in the right order. Patients with Parkinson’s disease have difficulties in sequencing tasks. Their deficits in sequential working memory have been associated with basal ganglia dysfunction. Here we demonstrate that altered parietal alpha and theta oscillations correlate with sequential working memory in Parkinson’s disease. We included 15 patients with Parkinson’s disease (6 women, mean age 66.0 years), 24 healthy young (14 women, mean age 24.1 years), and 16 older participants (7 women, mean age 68.6 years). All participants completed a picture ordering task with scalp EEG recording, where they arranged five pictures in a specific order and memorized them over a delay. When encoding and maintaining picture sequences, patients with Parkinson’s disease showed a lower baseline alpha peak frequency with higher alpha power than healthy young and older participants. Patients with a higher baseline alpha power responded more slowly for ordered trials. When manipulating picture sequences, patients with Parkinson’s disease showed a lower frequency of maximal power change for random versus ordered trials (Fmax) than healthy young and older participants. Healthy older participants showed a higher Fmax than healthy young participants. Compared to patients with Fmax in the alpha band (8-15 Hz), patients with Fmax in the theta band (4-7 Hz) showed a higher ordering-related accuracy cost (random versus ordered) in the main task and tended to respond more slowly and less accurately in an independent working memory test. In conclusion, altered baseline alpha oscillations and task-dependent modulation of alpha and theta oscillations may be neural markers of poor sequential working memory in Parkinson’s disease.