Objective: To determine the relation between apathy and neural oscillations in Parkinson’s disease (PD).

Background: Apathy in PD, characterized by lack of motivation, is often resistant to therapy, difficult to quantify and poorly understood. Prior studies have used incentivized motor tasks to measure apathy, but it is unclear whether these measures are reflected in neural oscillations. Normally, alpha (8-12 Hz) and beta (13-30 Hz) oscillations in the motor cortex decrease in power just before and during movement. We combine an incentivized motor task with EEG recordings to explore apathy in PD.

Methods: 12 apathetic (PD-A) and 12 non-apathetic PD (PD-NA) subjects on medication and 13 healthy control (HC) subjects performed a squeeze grip task in response to varying monetary incentives while EEG was recorded. Either $1, $10 or $50 were presented randomly and subjects were required to squeeze a hand grip to earn money (15 trials/money value). The amount earned in each trial was proportional to the grip force response (GFR), calibrated to each subject’s maximum squeeze force. We computed absolute and relative (percent change in power) time frequency data. Linear regression was performed to examine associations of power with apathy score and disease severity. ANOVA and Tukey Post-hoc tests were used to determine GFR and oscillatory power differences across groups.

Results: The mean GFR of PD-A subjects was significantly lower than that of PD-NA (p=0.003) and HC groups (p=0.0002), while no significant difference was observed between PD-NA and HC groups. At rest, PD-A subjects had higher absolute alpha power compared to PD-NA (p=0.047) and HC subjects (p=0.0003) in centro-parietal regions. A similar trend in beta power between PD-A and PD-NA groups was observed but was not significant. Resting alpha power was positively associated with apathy score (p=0.012) in PD irrespective of disease severity. Interestingly, despite higher baseline values, alpha power reduction relative to baseline was greater during motor execution in PD-A subjects compared to PD-NA (p=0.016) and HC subjects (p=0.026).

Conclusions: Our results suggest that because apathetic PD patients have a higher baseline alpha power, they require a stronger alpha reduction to execute movement. Absolute resting alpha power and the degree of alpha reduction may serve as potential biomarkers for apathy severity in PD.

References: Schmidt, L., d’Arc, B. F., Lafargue, G., Galanaud, D., Czernecki, V., Grabli, D., Schüpbach, M., Hartmann, A., Lévy, R., Dubois, B., & Pessiglione, M. (2008). Disconnecting force from money: effects of basal ganglia damage on incentive motivation. Brain, 131(5), 1303-1310. Meyniel, F. & Pessiglione, M. (2014). Better get back to work: a role for motor beta desynchronization in incentive motivation. Journal of Neuroscience, 34(1), 1-9.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/apathy-in-parkinsons-disease-is-associated-with-abnormal-alpha-oscillatory-behaviour-during-incentivized-movement/