Time-dependent effects of post-trial reinforcement, punishment or ECS on passive avoidance learning

Abstract

Three studies were performed to assess the effects of posttrial food reinforcement, ice-water punishment, and ECS on step-down passive avoidance learning in mice. The treatments were each administered at <5, 30, 60 and 90 sec after the footshock. One-half min of feeding beginning either 10 or 30 sec after the footshock increased the step-down latencies 24 hr later. This was considered to support the hypothesis that reinforcement facilitates learning by a direct influence on short-term memory processes. Posttrial ice-water punishment (10 sec immersion) disrupted learning only in the 60 sec postshock delay group. ECS (5.4 mA, 0.35 sec, across the ears) disrupted learning at all posttrial delays except 90 sec, with maximal effects immediately and at 60 sec, and minimal disruption at 30 sec. Similarities in the topography of the ECS and punishment curves suggested that some of the effects of posttrial ECS could be due to aversive properties of the ECS (acting directly on memory processes).