The postshock activity burst

When a rat receives an electric shock delivered to the floor of an enclosure, it reacts with frenzied activity. On shock termination, the activity persists for a brief period of time and then gradually gives way to a period of freezing. Subsequent grid shocks temporarily disrupt freezing, with the length of disruption determined by shock intensity (Experiment 1). The duration of this activity burst depends predominantly on the test shock intensity but not on the training shock intensity. The reverse is true for the probability of freezing, which is positively related to training shock intensity (Experiment 2). Based on this finding, it is argued that the activity burst is a UR, while freezing is a CR. Further support that freezing is a CR is provided by Experiment 3, which demonstrates that a delay, during which the rat is out of the shock-associated context, between the training and testing periods does not disrupt freezing. A topographical analysis of the behaviors making up the activity burst is provided by Experiment 4. The postshock activity burst was composed predominantly of head movement, turning, and rearing.