(A) Left, network firing rates during closed-loop control (black) and during replay of closed-loop control signals in open-loop (grey), along with corresponding control inputs UC (blue) and UH (yellow). These time series data were derived from culture 1. Note that in all instances, open-loop replay of input signals recorded from previous successful closed-loop control failed to clamp firing levels and resulted in erratic activity levels over the control epoch. Middle, time-averaged firing rates for both cultures during closed-loop control (black) and during subsequent replay of control signals in open-loop (grey). Right, average unit-to-unit cross-correlogram for both cultures (top, bin = 5 ms) and unit-to-unit synchronization structure for culture 1 (bottom) during optogenetic feedback control. Synchronization was defined as,
where Ncc is number of correlated events within ± 10 ms, and Ni and Nj are the number of spikes from units i and j used to calculated the cross-correlogram.
(B) Same as (A) for triangle optical stimuli modulated according to.
(C) Same as (A) for sinusoidal optical stimuli modulated according to.
(D) Same as (A) for pseudo-random binary sequence of optical pulses modulated according to.
(E) Same as (A) for continuous optical stimuli modulated according to.
Each protocol was performed in the same culture.
Periodic stimuli (panels A–C) were applied at 10 Hz so that the periodicity of evoked activity would be apparent in the correlation functions. In all cases, the 590 nm light was modulated according the standard control scheme (Equation 10 of ‘Materials and methods’). Note that each input type evokes a unique correlation and synchronization structure while still achieving accurate firing rate control.