Enhancement of conditioned fear during extinction

Abstract

Eight rats were given five sessions each of noncontingent shock at 2-, 3-, and 4-min intervals, followed by five sessions of extinction. The rats were immobile longer during the first two sessions of extinction than they were during the final two sessions of fear conditioning. The incubation effect was attributed to the prospective function as distinct from the retrospective function of the CS. Eysenck (1979) has suggested that, under some circumstances, animals undergoing extinction may show higher levels of the previously reinforced response than they did during conditioning (Le., the incubation effect). Noting that some neurotic behaviors are highly resistant to extinction, Eysenck theorized that aversive CSs may a~quire drive properties of their own that maintain CRs in the absence of the UCS.In a recent review, Mineka (1979) has argued that extinction of fear is at least partially independent of extinction of avoidance-escape responding. Several studies have suggested that subjects may exhibit fear even when avoidance responding has ceased following extinction or flooding (Coulter, Riccio, & Page, 1969;Kamin, Brimer, & Black, 1963;Mineka & Gino, 1979; see also Starr & Mineka, 1977). These fmdings suggest that levels of conditioned fear may be higher than might be expected on the basis of avoidance response data. In addition, Mineka and Gino (1979) have suggested that conditioned fear may peak at the time that the subject ceases to respond during extinction.Several studies have directly shown that fear levels were enhanced if the subjects experienced a brief, unreinforced CS presentation after acquisition but before a series of regularly presented extinction or flooding trials (linton, Riccio, Rohrbaugh, & Page, 1970;Rohrbaugh, Riccio, & Arthur, 1972). However, only in the Rohrbaugh et al. (1972) study was the total time spent in the training apparatus equated for all groups; and in this study the enhancement effect seemed rather transitory. Furthermore, in all three studies, only one brief acquisition training session was given, followed · quickly by a brief unreinforced CS presentation and the other extinction or flooding trials. Recently, Boyd (1981) reported that incubation was partially related to shock intensity and that avoidance Nicholas R. White is now at the University of Toronto. The study was supported by a research grant from the Natural Science and Engineering Research Council of Canada to the second author.behavior was increased only for high-shock groups despite prolonged exposure to nonreinforced CS.The main purpose of the present study was to determine whether conditioned fear would be enhanced during extinction after a prolonged period of noncontingent shock presentation. Conditioned fear was measured by amount of time spent in freezing or immobility. In addition, we attempted to determine if food-deprived rats would show a higher level of fear than nondeprived rats. METHOD SubjectsEight male Walker-Walker hooded rats were used in this study. All subjects were experimentally naive and ha...