Disruption and Recovery of the Orienting Response Following Shock or Context Change in Preweanling Rats

Abstract

Previous research has shown that placement of preweanling rats in an unfamiliar environment inhibits both heart rate and behavioral orienting responses to an auditory stimulus, and that the orienting response gradually reappears during the following 15 min. Four experiments designed to evaluate two potential explanations of this effect were conducted. If the arousal induced by an unfamiliar environment disrupts sensory information processing, so should the arousal induced by mild electric shock. In two experiments, the orienting response was inhibited in proportion to number of shocks received and rate of recovery was comparable to that observed in the unfamiliar environment. New environments also contain many unfamiliar stimuli which may overload the rats' limited information processing capacity. In two experiments a change in environmental stimulation was shown to inhibit the orienting response. Recovery of the orienting response followed the same time course as that seen following shock or placement in an unfamiliar environment. Although the results of this study clearly demonstrate environmental inhibition of the orienting response, they provide little support for either the "arousal" or the "information overload" hypotheses of orienting response inhibition. The implications of these data for current theoretical conceptualizations of the orienting response are discussed.

Latent habituation of the orienting response in the preweanling rat

“…These findings have obvious conceptual and temporal similarities to the results of the present paper. In combination with the present results (see also Richardson et al, 1988, andSaiers et al, 1990), the recent work by Carew and his colleagues firmly establishes the generality of inhibition of unconditioned reactions to sensory stimuli. This effect is seen not only across species (rats and Aplysia), but also with different types of unconditioned responses (orienting and defensive responses).…”

“…The same pattern of results following shock was also found in Experiment 1 of Saiers et al (1990; but see Experiment 2 of that study).…”

“…When an auditory stimulus that normally elicits an orienting response is presented 30 sec after animals have been placed in an unfamiliar environment, shocked, or experienced a shift in contextual cues, no evidence of a cardiac or a behavioral orienting response is detected (Richardson et al, 1988;Saiers, Richardson, & Campbell, 1990). If the orienting response is a necessary precursor for subsequent stages of information processing (e.g., Ohman, 1979), then inhibition of this response should preclude the formation of a neuronal representation of the eliciting stimulus.…”

“…The only difference was that the four presentations of the auditory stimulus began either 30 sec or 15 min after the animals had been given a brief series of electric shocks. This procedure had been shown to inhibit the orienting response in an earlier study (Saiers et al, 1990). As in the preceding experiment, all animals were given a second series of stimulus presentations 15 min after the first in order to determine the effects of shock-induced inhibition of the orienting response on habituation.…”

“…The context change consisted of altering the olfactory, visual, and auditory characteristics of the test environment. This procedure is known to inhibit the orienting response to an auditory stimulus (Saiers et al, 1990). Fifteen minutes after the initial stimulus sequence, the same auditory stimulus was presented to determine what effect, if any, inhibition of the orienting response had on habituation of the orienting response.…”