Fig. 3.

Chronic evaluation of ECoG-electrode parameters and HFB-power. (A) Mean HFB-power per run (65–95 Hz) HFB-power (mean per run) during the Baseline-task in the motor strip (home use pair e2-e3) in black and dlPFC-strip (best performing pair, e9-e11) in grey. The dotted lines are the linear trend lines. Shaded area surrounding the line represents the standard deviation per run. Triangles represent data acquired after the research period. Note: motor and dlPFC-strips have independent analog amplifiers on the device, therefore the absolute HFB-power values of motor and dlPFC cannot be compared. (B) HFB-power (pair e2-e3 of the motor strip) during the active (black) and rest (grey) phase of the Target-task. Note that due to the analogue filtering on board of the device (center frequency 80 Hz, bandwidth 2.5 Hz; effective frequency range at these settings is 80 ± ∼10 Hz) the power values differ from the calculated power values in panel A. The dotted lines are the linear trend lines, the shaded area surrounding the line represents the standard deviation, and the triangles represent data acquired after the research period. Note that HFB power appears to stabilize after week 112. (C and E) Electrode pair impedances over time. Colored lines indicate values per electrode pair, averaged per month. In black the mean over all pairs of the motor strip, in red the pair used for control. Panel A shows the impedance values obtained using stimulation at 0.25 V. Panel C shows the values obtained after stimulation settings were increased to 0.7 V in April 2016 when some recordings using 0.25 V reached the maximum displayable value of 4000 Ω. Triangles represent the data collected after the research period (from November 2017). (D) Linear regression results of the impedances in panels A and C. During the first 5 months, a significant increase in impedance was found in all electrode pairs. From April 2016 onwards the impedances stabilized for all but 4 pairs (e1-e3, e1-e4, e2-e4 and e3-e4).