Figure 1.

Electrode localization, experimental setup and representation of the freezing index. (A) Localization of electrocorticography (ECoG) electrodes. The eight contacts (C1–C8) are visualized in the merged image of preoperative MRI and postoperative CT (left). C8 is the contact closest to the DBS bone hole. The white arrow points to the primary motor cortex. A reconstruction of the cortex and the eight contacts relative to the primary motor cortex (black arrow) is shown in the right figure. (B) Localization of the STN electrodes (white arrow) in the merged image of preoperative MRI and postoperative CT. (C) Experimental setup and protocol. Patients were asked to walk barefoot while completing a 10 m (5 m one way) back-and-forth timed up-and-go task at a self-selected pace with sensors attached to the lower limbs. The instant coordinates of the sensor were captured through an optoelectronic motion tracking system hanging on walls on both sides. Synchronized ECoG potentials were recorded through an extended cable. (D) The representative diagram of the freezing index (FI). The blue line represents the vertical position of the foot. The green line represents the forward position of the foot. The red line represents the FI. When the vertical kinematic rhythm becomes irregular and the forward motion stagnates, FI rises and exceeds the 3-point threshold (solid black line). Notably, if the FI drops below ‘3’ but then rises back, with the lowest value still over ‘2’ (grey dashed line), we consider this as one continuous freezing event rather than two. Thus, the diagram shows one continuous freezing event lasting from time point I to time point III. Because FI does not drop below ‘2’, time point II does not mark the end of this freezing event.