There are two explanations for the observed high PAC in freezing trials. First, PAC peaked only when freezing occurred while maintaining a normal level during non-freezing walking. Second, PAC was constantly at an abnormally higher level during freezing trials, not limited to the period where freezing occurred. To investigate, we compared PAC levels between different walking episodes (Fig. 3A and B). We found that PACs of the FN and FF were at similar levels (P = 0.147, signed-rank test), while both were significantly higher than that of the NN (P = 0.003 for FN, P = 0.007 for FF, signed-rank test, Fig. 3C). This trend was evident in almost each subject (Fig. 3D) and also held true after correcting the different FI level using linear mixed effect models [FN versus NN: β = 0.427, 95% confidence interval (CI) = 0.104 to 0.749, P = 0.010; FF versus NN: β = 0.615, 95% CI = 0.060 to 1.170, P = 0.030]. These results indicated the non-freezing walking episodes in freezing trials were also electrophysiologically abnormal.
