Experimental set-up.

(A) A real-time closed-loop in vitro set-up for experimentally estimating the PRC at a fixed firing rate, based on a Proportional-Integral-Derivative (PID) controller and on a reactive-clamp paradigm, was employed to rapidly and optimally explore the dependency of the PRC of PCs on the cell’s firing rate. To this aim, a brief external current-pulse (B-D at different scales) was repeatedly delivered at different phases φ of the cell cycle (E), and the resulting impact on the time of the next AP was quantified as a phase delay or of advance Δφ (E).