Effects of current pulses on the sustained discharge of visual cells of Limulus

Current pulses were used in the eccentric and retinular cells of the Limulus lateral eye to produce changes in the interspike interval of the discharge sustained by a constant light level. The effects on the interspike interval of hyperpolarizing and depolarizing perturbations, applied at various delays from the previous spike, were measured for different intensities and durations of the current pulse. The results show that when the perturbations were applied in the first part of the interval, effects contrary to what is normal were produced (i.e, hyperpolarizing pulses decreased the interspike interval instead of increasing it and vice versa for depolarizing pulses). Here we discuss briefly the implications on neural encoding models.