The nature of the activity deficit produced by inescapable shock

Two experiments investigated the nature and etiology of the reduced activity in the presence of shock produced by prior exposure to inescapable shock. Previous experiments have demonstrated this deficit in the presence of gridshock. However, gridshock hurts less if movement across the grids is reduced. It is thus unclear whether the inescapable-shock-produced deficit represents a facilitation of learning to reduce movement across the grids in order to alleviate pain or is an “unconditioned” reduction in movement in response to shock. The first experiment tested these possibilities by examining the effects of inescapable shock on subsequent movement during shock delivered via fixed tail electrodes to freely moving subjects. Inescapably shocked subjects still moved less in response to shock than did escapably shocked and restrained control subjects. Experiment 2 examined the possibility that this deficit occurs because unconditioned movement in response to shock during pretreatment diminishes after a few seconds, the reduction then being adventitiously reinforced by shortly ensuing shock termination. Activity during inescapable shock was closely monitored by ultrasonic motion detection. Although activity did decrease across trial blocks, the required within-trial patterns did not occur. Shock-elicited activity did not diminish after a few seconds of shock, but remained unchanged across the 5-sec shock presentations.