EP 54. Alpha activity in Fronto-Parietal Areas is modulated by Dopamine in Switching Visuospatial Attention in Parkinson’s Disease

Abstract

Alpha-band activity (8–12 Hz) is a prominent electrophysiological signal in the human brain. Alpha power is known to be modulated by visuospatial attention in healthy humans( Thut et al., 2006 , Klimesch, 2012 ). Patients with Parkinson’s disease (PD) show a decrease in attentional control and deficits in switching of attention ( Aarsland et al., 2010 ). Here, we studied the role of alpha power in switching of visuospatial attention in PD. In PD, motor symptoms improve with dopamine replacement medication. We additionally studied whether dopaminergic medication alters the network activity in the alpha band during visuospatial attention. 20 subjects with diagnosed PD (15 male, 55 ± 10 y) performed the task in which they had to attend either to the left or right visual hemifield, indicated by a central cue. After a delay (1200 ms) a visual stimulus was presented in each hemifield. After another randomly chosen time, one of the two stimuli changed its color. A button press was required when the color change appeared on the cued side. We measured reaction times, and brain activity with magnetoencephalography. To analyze frequency bands of brain activity, we applied fast Fourier transform on the neural data. Subjects performed the task after 12 h withdrawal from dopamine replacement medication (“OFF”) and after receiving L-DOPA (“ON”). Before and after receiving L-DOPA, we performed the Unified Parkinson’s Disease Rating Scale (UPDRS) to assess efficiency of L-DOPA. We compared switching with not-switching trials, with “switching” meaning two successive trials required attention to opposite hemifields, “not-switching” meaning two successive trials required attention to the same hemifield. Comparison was done between and within medication factor (ON/OFF).UPDRS scores showed significant improvement of motor symptoms after receiving L-DOPA. During OFF, subjects responded faster in not-switching than in switching, whereas during ON there was no difference in reaction times. During OFF, we found a decrease of alpha power for switching relative to not-switching in right parietal (5–15 Hz) and right frontal areas (10–17 Hz) during the delay period. During ON, we found a decrease of alpha power for switching relative to not-switching in right occipital regions (2.5–15 Hz) during the cue period. Finally, we found a positive correlation between alpha power (8–12 Hz) and reaction times during OFF for switching, but not for not-switching. Faster reaction times for not-switching during OFF might reflect a strong focus on the previously attended side. Switching attention during OFF is therefore more difficult, which is reflected in less relative alpha power for switching, and thus more activity, in the fronto-parietal network. L-DOPA, therefore, increases flexibility for switching by lessening suppressing alpha-band activity in the fronto-parietal network. This could be achieved by better visual processing of the cue, as reflected in less alpha power during the cue period in visual areas.