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In experiments using a total of 144 albino rat subjects, the authors assessed the ability of fear-weakening treatments to prevent fear renewal (relapse). Conditioned suppression of operant behavior served as the measure of fear in an A-B-A (acquisition-treatment-test) renewal paradigm. In Experiment 1, 100 nonreinforced exposures to a feared cue during treatment (extinction) did not reduce fear renewal relative to 20 exposures. In Experiment 2, explicitly unpaired (EU) treatments thwarted both renewal and reacquisition. In Experiment 3, conditioned inhibition (CI) and differential conditioning (DC) treatments weakened renewal and resisted both reacquisition and a form of reinstatement. In Experiment 4, EU, DC, and CI treatments all thwarted renewal. Evidence suggested that the ability of the treatments to do so reflected the combined effects of transfer of extinction across treatment and test contexts and habituation to the unconditioned stimulus.

In three experiments, groups of albino rats received one strictly simultaneous pairing ofa 4-sec auditory conditioned stimulus (CS) and a 4-sec I-rnA shock unconditioned stimulus (US). Other groups received a backward pairing, in which the US began before the CS, or a forward pairing, in which the CS began before the US. Control groups received only the US or received both the CS and the US but widely separated in time. Later, the CS was presented while the rats licked a drinking tube for water, and CS-elicited suppression of licking was taken as an index of the Pavlovian conditioned response (CR). It was found that groups receiving a single forward or a single simultaneous pairing suppressed more than groups that had received a backward pairing; and the backward groups, in turn, suppressed more than the control groups. It appears, then, that excitatory fear conditioning, as reflected in conditioned suppression of licking in rats, can be produced in a single trial by both backward and simultaneous conditioning procedures.

In two expertments, we examined the effects of a wide range of interstimulus intervals (2.5, 15,45, 120,135, and 405 sec) on one-trial context fear conditioning with rats. Here, the interstimulus interval (ISI) denotes the time between placement in a conditioning chamber and the onset of a single footshock. On the conditioning day, we observed that the rats' behavior at the time of shock onset varied systematically across lSI values. On the subsequent test day, we used context-evoked freezing as a measure of context conditioning and found the well-known inverted V-shaped lSI function. We also found that conditioned freezing for the shortest lSI values was concentrated early in the test session, whereas freezing at longer ISIs was distributed more evenly throughout the test session. The freezing results found here are more consistent with the literature on conditioning with punctate cues than are previously described results from one-trial context fear-conditioning procedures.

Conditioned suppression was found in groups of albino rats which had received different truly random control procedures. The degree of conditioning did not covary with the number of CSs, the number of USs, or the number of chance pairings. Conditioning was determined by the location of pairings. If pairings occurred before nonpairings, then excitatory conditioning was found. If nonpairings occurred before pairings, then excitatory conditioning was not found. a Requests for reprints should be sent to James 0

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