Fig 2. Characterization of analog feedback system for neural oscillation modification.
(A), Bode diagram of filter response as simulated in LT-SPICE, showing rapid roll-off and linearized phase behavior in the least-attenuated portion of the passband. (B), filter performance on a representative sample of pre-recorded data (Vin = input, Vout = output), demonstrating extraction of alpha (8–16 Hz) activity and sign inversion. This trace also provides an example of a waveform that would be applied as the stimulation in the Closed and Brain conditions. (C), phase response of filter on a signal (pink noise filtered to the alpha band) with predominant power within the filter passband. The histogram shows the difference between the phase of the signal provided at Vin and the phase at Vout, as computed via Hilbert transform on both signals. The phase shift of the filter is, as desired, predominantly at or near 180°. (D), timing of the stimulation periods for the in vivo experiment. The mean was 8.97 seconds, versus a target of 10 seconds, with all stimulation periods between 7.74 and 10.74 seconds in length.