Given that PAC in M1 can be related to bradykinesia in Parkinson’s disease,15 we assessed if higher PAC during freezing trials could be induced by the reduced walking velocity per se rather than freezing. We instructed five subjects to complete extra trials of intentionally fast- and slow-velocity walking, and controlled the factor of freezing by analysing non-freezing trials only (n = 72). We found that the average speed (total distance/total time) was significantly different among fast, normal and slow-speed trials (tested through linear mixed effect models, Supplementary Fig. 4A), while no difference was observed in PAC (Supplementary Fig. 4B and C). This suggested that PAC was not directly associated with walking velocity, and the higher PAC observed in freezing trials was unlikely to be induced by velocity change.
