Fig. 2.

(A) Spinally transected rats that receive a noxious shock to one hind leg whenever the leg is extended (Master) exhibit a progressive increase in flexion (response) duration over 30 min of testing, which reduces net shock exposure (Grau et al., 1998). Rats that receive the same amount of noxious stimulation, but independent of leg position (Yoked), fail to learn. (B) Spinally transected rats that have previously undergone training with controllable stimulation (Master) learn faster (positive transfer) than untrained (naïve) controls (Grau et al., 1998). Rats that have previously received uncontrollable stimulation (Yoked) exhibit a learning impairment. Importantly, this impairment is not due to an inability to perform the target response; rats that have previously received uncontrollable stimulation exhibit a flexion response when shock is given, but this response-contingent stimulation does not induce an increase in flexion duration. (C) Exposure to variable intermittent tailshock (VIS) for 6 min (180 shocks) impairs learning for 48 hrs (Crown et al., 2002b). (D) Prior exposure to controllable shock (Pretrained) fosters learning when animals are tested with a higher response criterion (Crown et al., 2002a). Under these conditions, naïve (untrained) rats fail to learn. Pretrained rats are able to learn and this is true independent of whether they are tested on the same [ipsilateral (ipsi)] or opposite [contralateral (contra)] leg.