Signaled tailshock is perceived as similar to a stronger unsignaled tailshock: Implications for a functional analysis of classical conditioning.

Abstract

Water-deprived rats given fixed-electrode, variable-intensity tailshock at random times rated each trial by pressing either a "high-aversiveness" or "low-aversiveness" lever in order to obtain water. Trials on which a warning signal preceded tailshock resulted in more "high-aversiveness" leverpressing than did otherwise equivalent unsignaled trials. The magnitude of this effect increased and decreased as a function of several parameters including signal-shock interval, signal duration, and range and absolute value of shock intensities but was never reversed despite efforts to achieve such a reversal. Variation in the size of the effect as a function of signal parameters as well as lick suppression scores indicated that the signal had acquired aversive characteristics, which suggests that the effect of the signal on lever choice was due largely to the aversiveness of the signal summating with the aversiveness of the tailshock. Several hypotheses concerning factors that might have either masked or prevented classically conditioned preparatory responses elicited by the signal from reducing tailshock aversiveness were tested and rejected. Despite the greater aversiveness of the signaled condition, when given the choice of receiving or not receiving the signal, the animals displayed a preference for signaled tailshock. Implications for the role of preparatory responding both in the preference-for-signaled-shock phenomenon and in classical conditioning are discussed.

Effects of predictability on the welfare of captive animals

“…It appears, therefore, that predictable shock may be more aversive (in terms of physiological stress responses) than unpredictable shock under certain experimental conditions. Pitman et al (1995) showed that greater predictability of shock was associated with higher plasma corticosterone and norepinephrine levels, taken to be indicative of chronic stress, supporting the conclusions of Miller et al (1983). Pitman et al (1995) believe that signals reliably predicting shocks cause sensitisation of central neural control of adrenocortical activity, whereas unpredictable shocks cause habituation of the central nervous system to occur.…”

“…This finding implies that preference does not necessarily indicate the stressfulness of the various conditions. Arthur (1986) claims that it is nonsensical to conclude that predictable shock is less stressful when there is evidence (Miller et al, 1983) that rats experience predictable shock as more intense. It appears, therefore, that predictable shock may be more aversive (in terms of physiological stress responses) than unpredictable shock under certain experimental conditions.…”

“…The discrepancy between behavioural preference for predictable over unpredictable shock (reviewed by Badia et al, 1979) and the physiological stress response which does not wholly support this conclusion suggest that behavioural and physiological measures of stress are not analogous. Miller et al (1983) trained water-deprived rats to press a 'high-aversiveness' or 'lowaversiveness' lever in response to a fixed-electrode variable-intensity tail shock, in order to obtain water. This enabled the experimenters to gauge how intense the rats perceived the shocks to be.…”

Male-Specific Conditioned Pain Hypersensitivity in Mice and Humans

“…All extant studies in humans were conducted using repeated pairings of discrete, noxious thermal or electrical stimuli as the unconditioned stimulus (UCS), usually with neutral visual or auditory stimuli as the conditioned stimulus (CS). Although conditioning-based methods are increasingly used in preclinical pain research to quantify pain [12], it has been virtually impossible to demonstrate conditioned hypersensitivity in rodents [13,14], even though electric shocks are used routinely as the UCS in fear-conditioning paradigms and conditioned stress-induced analgesia is a well-studied phenomenon [15].…”

The multiple determinants of observing behavior

“…Because observing behavior has been seen in situations that appear to be devoid of both overt and covert preparatory responding (e.g. Miller et al 1983), preparatory responding is not a likely alternative explanation of observing behavior that could obviate the need for other explanations such as secondary reinforcement. However, the absence of preparatory responding in these cases stems largely from the use of specific preparations that make preparatory responding unlikely, such as fixed electrodes for shock delivery.…”