Electromyographic Characteristics of Postactivation Effect in Dopamine-Dependent Spectrum Models Observed in Parkinson's Disease and Schizophrenia.

This study aimed to test the hypothesis that the postactivation effect (PAE, involuntary normal muscle tone) is modified by dopaminergic mechanisms. The PAE was tested with surface electromyography (sEMG) in the "off medication" phase in participants with Parkinson's disease (PD) and in the "on medication" state in participants with schizophrenia (SZ), which modeled hypodopaminegic conditions, and in participants with PD "on medication" (PD) and in participants with SZ "off medication" (SZ) state which modeled the hyperdopaminergic conditions. Healthy age-matched participants constituted the control group (HC, = 11). In hyperdopaminergic models, PAE was triggered in 71.3% of participants in SZ and in 35.7% in PD conditions. In the hypodopaminergic models, PAE was triggered in 12% in SZ and in 21.4% in PD conditions. In the HC group, PAE was present in 91% of participants. In the HC and PD groups, the mean frequency and correlation dimension of sEMG at PAE was higher than that during voluntary isometric contraction. In conclusion, in hypodopaminergic models, PAE triggering was inhibited. The manifestations and EMG characteristics of PAE in people with PD or SZ may indicate dopaminergic dysfunction.