When generating a stimulation signal comprising stimulation pulses delivered to a target area of a human or animal body, an electrophysiological signal measured from the body for closed-loop control of the stimulation signal, is sampled, at a sampling frequency in an analogue-to-digital converter for deriving a feedback signal for closed-loop control of the stimulation signal. The generation of the stimulation signal and the sampling of the electrophysiological signal are synchronised and have a relative phase selected to cause the sampling to occur outside the stimulation pulses, which prevents the effect of the stimulation pulses from interfering with the digital electrophysiological signal, whiles allowing maintenance of Nyquist-Shannon rules and the integrity of the discrete Laplace transform (z-transform) required in discrete control theory.