Figure 1. The short latency response to subthalamic DBS and the electrical stimulus transient are independent signals.

(A) Within a single EEG electrode, responses from FP1-M2 during 20 Hertz left subthalamic DBS show reversal of the stimulus artifact by inversion of the anode and cathode contacts (3+2- and 3-2+, blue and green traces, respectively). The composite ERP demonstrate three discrete peaks at approximate latencies of 1, 6 and 22 milliseconds after stimulus onset (P1, P2, and P3, respectively, red traces). The inset shows the short latency response over a shorter time scale, demonstrating that it retains the same polarity, regardless of the polarity of the bipolar stimulus transient that precedes it. Furthermore, the polarity of the millisecond latency peak shares the same polarity as the later peaks in the response, both in the two anode/cathode pairings (blue and green traces) and in the composite ERP (red trace). (B, C) Across different EEG electrodes, the electrical stimulus transients (blue and green traces) but not the short latency brain response (red traces) in F4-M2 are reversed relative to FP1-M2 and FP2-M2, indicating that the stimulus artifact from the DBS pulse (the large peaks in the blue and green traces) and the short latency brain response (red traces) are spatially independent and cannot localize to the same source. Each trace is the average of approximately 9000 stimulation events in each of the anode-cathode pairings.