Preventing Recovery Of Learned Fear: A Novel Extinction Procedure
Following fear conditioning in a typical extinction experiment, animals are returned to and remain in the apparatus in the absence of shock until fear is extinguished. The effect of extinction is often temporary: with passage of time fear recovers. This recovery is thought to result from an inhibitory memory acquired during extinction that temporarily suppresses the otherwise intact fear memory. In contrast to the typical extinction procedure, we recently used a modified extinction procedure in which animals, following contextual fear conditioning, were exposed to the conditioning apparatus in the absence of shock for a brief period (30-sec); thus, animals were removed from the apparatus before an opportunity developed to recall fear to a significant degree. A retention test the next day revealed that the brief-exposure was effective in weakening retention of fear. What remained to be determined were the endurance of the brief-exposure effect and the degree to which it could be manipulated. To this end, in the present study, male Long-Evans rats underwent contextual fear conditioning followed 24 hr later by the brief-exposure procedure. Fear conditioning consisted of placing rats in a dark compartment for 120 sec followed by a single footshock (0.8 mA, 0.5 sec); the brief-exposure procedure consisted of confining the animals to the dark compartment in the absence of shock for 0 sec, 30 sec, 60 sec or 180 sec or for two 30-sec exposures separated by 10 min (the 30-sec/10 min/30-sec condition). Level of fear (freezing behavior) was monitored during the exposure conditions and a retention test to assess recovery of fear was administered either 1 or 13 days later. The results indicated that fear increased during exposure in all conditions with one exception: fear decreased in the 30-sec/10 min/30-sec condition. In addition, retention of fear decreased in the short term (retention test 1 day later) and recovered in the long term (retention test 13 days later) in all conditions with one exception: retention of fear did not recover in the 30-sec/10 min/30-sec condition. To account for these results, we propose that learning occurs during the exposure conditions, but the type of learning is dependent on the level of fear during the exposure. If fear is relatively high (as a result of 30, 60 or 180 sec exposure) inhibitory learning (or equivalently prediction error) occurs, the original fear memory is temporarily suppressed and retention of fear recovers. If fear is relatively low (as a result of the 30-sec/10 min/30-sec condition) the animal learns to associate weak fear with the apparatus, the original fear memory is displaced and retention of fear does not recover.
Society For Neuroscience 2015 Annual Meeting
October 17-21, 2015
Allen M. Schneider; P. E. Simson; Molly J. Lichten , '15; Jennifer L. Walsh , '15; Daniel J. Kalamarides , '14; E. Carr Everbach; and L. G. Kirby.
"Preventing Recovery Of Learned Fear: A Novel Extinction Procedure".