Objective: In this study, we aim to understand the functional role of β-γ phase amplitude coupling (PAC) during repetitive movement tasks and its relationship with motor impairment.

Background: Previous study have reported enhanced PAC between β (13-30Hz) and broadband γ (50-150Hz) activities from surface EEG at rest of patients with Parkinson disease (PD) [1], but it is unclear how abnormal PAC is involved in the pathophysiology of PD motor symptoms.

Method: We analyzed EEG signals recorded at rest and during various motor activities in 19 PD patients and 20 healthy controls. The motor tasks consisted of repetitive finger pressing and finger tapping, performed at the subjects’ own pace and at their fastest pace. Source analysis was applied on individual EEG signals to obtain the source signals extracted from 4 brain regions involved in motor control (i.e. premotor cortex, primary motor cortex, primary somatosensory cortex and primary somatosensory complex). Transient PAC values were calculated in each region by mean vector length [2].

Results: PAC averaged across the whole movement period was enhanced in PD patients in the pressing task compared with controls. However, the averaged PAC was similar between patients and controls in all tapping tasks. Besides, we examined the dynamics of PAC during motor transients. When controls performed the pressing task, dynamic PAC decreased around the onset of the pressing and recovered subsequently. A similar pattern was also observed at the offset of pressing and at the onset of slow tapping. In PD patients, the dynamical pattern of PAC was similar in pressing, where performance did not differ from controls. However, in slow tapping, in which the slope of muscle activity was reduced in PD patients, the modulation of the PAC was less pronounced than in the controls.

Conclusion: Persistence of PAC differences during the pressing in which patients perform normally, while lack of PAC differences during the tapping tasks in which patients showed abnormal motor actions, suggest that exaggerated β-γ PAC does not directly signal impaired motor behavior in PD patients. Our findings suggest that transient PAC changes may be linked to a change between distinct movement states.  Exaggerated PAC, as found in PD patients in the resting state and under some movement conditions, may reflect the abnormal invasion of a normal inhibitory mechanism into adjacent movement phases.

References: [1] Gong et al., 2020. Brain [2] Canolty.R.T et al., 2006. Science

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MDS Abstracts - https://www.mdsabstracts.org/abstract/movement-related-dynamics-of-%ce%b2-%ce%b3-phase-amplitude-coupling-in-repetitive-movement-tasks-of-parkinson-disease/