Behavioural strategies of aggressive and non-aggressive male mice in response to inescapable shock.

The effect of exposure to inescapable long-duration shocks of moderate intensity on intershock activity and on subsequent escape or avoidance performance was studied in aggressive and non-aggressive male mice. The activity of the non-aggressive mice was severely suppressed during the inescapable shock session, while that of the aggressive males was hardly influenced. The decremental effect of prior shock exposure on subsequent response latency and activity in an active two-way escape or avoidance task was greater in the non-aggressive than in the aggressive mice. There was no evidence that learned inactivity or learned helplessness (an associative deficit) could explain the results. Instead, individual differences in behavioural strategy in response to threatening situations appeared to account for the effects of inescapable shock. Aggressive male mice predominantly adopted an active behavioural strategy in challenging situations, which resulted in persistent attempts to exercise control over the external situation and hence in a sustained tendency to initiate responses. Non-aggressive mice primarily assumed a passive strategy; their tendency to exercise control was low, which readily resulted in a reduced tendency to initiate responses.