Duration and nature of retrograde amnesia produced by stimulation of caudate nucleus

Rats given a single brief footshock while standing upright and drinking from a water tube were slow in returning to the tube and drinking when tested 24 hr later. When single pulse bilateral electrical stimulation of the caudate nuclei followed the footshock they were quick to return and drink. This retroactive effect of the stimulation was temporally graded. It resulted from a retrograde amnesia produced by the stimulation. A delay of 5 min was effective. A futher experiment repeating the treatment a second time indicated that a 15 min delay was not effective. Another experiment repeated the treatment four times. Rate of learning (avoidance of the tube) increased as the delay of stimulation increased indicating that the stimulation was stopping the encoding of short-term associative learning into memory at the time of its application.