Explicit Disassociation of a Conditioned Stimulus and Unconditioned Stimulus During Extinction Training Reduces Both Time to Asymptotic Extinction and Spontaneous Recovery of a Conditioned Taste Aversion.

Conditioned taste aversions (CTAs) may be acquired when an animal consumes a novel taste (CS) and then experiences the symptoms of poisoning (US). When later given a choice between the poisoned taste and water, the animal will avoid the taste previously associated with malaise. This aversion may be extinguished by repeated exposure to the CS alone. However, following a latency period in which the CS is not presented, the CTA will spontaneously recover (SR). Thomas et al. (2005) have used an explicitly unpaired (EU) procedure to thwart renewal of a conditioned emotional response (CER) following extinction. We applied similar procedures to the CTA paradigm. Sprague-Dawley rats acquired a CTA [3 pairings of oral saccharin (SAC) and i.p. lithium chloride (LiCl)] followed by extinction training (EXT) consisting of either (a) CS-only exposure or, (b) exposure to SAC and LiCl on alternate days (i.e., explicitly unpaired: EU). Both extinction procedures resulted in> 90 % reacceptance of SAC although the EU-EXT procedure significantly decreased the time necessary for rats to reach this criterion (compared to CS-only controls). Rats were subsequently tested for SR of the CTA upon re-exposure to SAC following a 30-day latency period of water drinking. Rats that acquired a CTA and then underwent the CS-only extinction procedure exhibited a significant suppression of SAC drinking during the SR test (as compared to their SAC drinking at the end of extinction). However, animals in the EU extinction group (EU-EXT) did not show such suppression in drinking compared to CS-only controls. These data suggest that the EU-EXT procedure may be useful in reducing both time to extinction and the spontaneous recovery of fears. The findings are clinically relevant as we seek the development of treatments for deficits in fear extinction [e.g., Post Traumatic Stress Disorder (PTSD), phobias]