Apathy in Parkinson's Disease: EEG Microstate Characteristics

Apathy is a cognitive, behavioral, and emotional disorder marked by a decrease in goal-directed activities as well as affective flattening. This multifaceted disorder has been described in Parkinson's disease as a highly common neuropsychiatric feature. The pathophysiology that underlies apathy, however, is still not entirely understood. The major goal of this study was to determine the microstate correlations of apathy in Parkinson's disease. This study involved patients with the diagnosis of idiopathic Parkinson's disease. Based on the Apathy Evaluation Scale criteria, Parkinson's disease groups were divided into two main groups- apathetic and non-apathetic. Patients underwent clinical, motor, and demographic characteristics as well as neuropsychometric evaluations. Spontaneous EEG brain activity was recorded, and a microstate analysis was conducted. The clinical and motor functions of the apathetic and non-apathetic groups did not differ significantly; nevertheless, the apathetic group performed worse on several executive function and memory tests. A comparison of EEG microstates between the apathetic and non-apathetic groups found that the apathetic group had an increase in the duration and coverage of microstates B and E, whereas the frequency of Microstate D decreased. Additionally, in patients with apathy, an increased transition was observed from Microstate A > B, C > E and C > G. Our findings suggest that the increased transitions from Microstate A to B and from C to E and G, along with an increase in Microstates E and B and a decrease in Microstate D, may reflect changes in the activity or functional connectivity of several large-scale brain circuits in Parkinsonian apathy. On the other hand, Microstate E could be the fundamental microstate reflecting changes associated with the Default Mode Network in Parkinsonian apathy.