**3. Behavioral avoidance as a precursor for increased arousal**

For some time, the acquisition and performance of avoidance behavior was used as a tool to increase arousal in studies of physiological responsiveness in monkeys (e.g. stress-induced hypertension) because it was obvious to the investigators that control over the stimuli did not necessarily lead to a reduction in arousal (Forsyth, 1968; Forsyth, 1969; Natelson et al., 1976; Natelson et al., 1977). Since that time, avoidance learning fell out of favor as such a tool and was generally replaced by inescapable stressor paradigms. Therefore, with our rodent model of acquisition and extinction of active avoidance behavior, we questioned whether the process of acquiring avoidant behavior would influence general arousal outside of the avoidance-training context, which was not the case for some of the monkey studies (Forsyth, 1968; Forsyth, 1969).

Having established strain and sex differences in the acquisition and extinction of active avoidance, as well as differences in innate reactivity between strains, the question became whether the process of acquiring avoidant behavior would influence general arousal outside of the avoidance-training context. There are three possible periods of time startle reactivity may show changes as a function of acquiring lever-press avoidance and each would have associated with it a different theory of how the learning procedure was affecting general sensory reactivity. First, based on the above inescapable shock model, one could hypothesize that startle reactivity should be increased within days of the first few training trials, following the sessions the rats experience the most shock. Second, if the development of avoidant behavior follows the trajectory of developing anxiety, then one could hypothesize that startle reactivity should increase over acquisition. Yet, there is also a third option. That is, startle reactivity could increase if the association between the signals and the consequence becomes less certain. In this third possibility, startle reactivity could be increased if there is a change in the relationship between the signals that represent threat and the consequences following acquisition (such as conducting extinction trials). Another consideration is that only certain animals may be affected in a way that increases their general arousal. Strain differences in both acquiring the avoidant behavior and resistance to extinguish it may be a sign of anxiety vulnerability that could also be reflected in a change in general arousal (reflected as a persistent change in startle reactivity).
