Extinction of a conditioned taste aversion in rats: I. Behavioral effects.

The literature is divided over whether a conditioned taste aversion (CTA) can be fully extinguished. In Experiment 1, we created a powerful aversion in 54 rats by pairing the taste of 0.0025 M NaSaccharin (CS) with intraperitoneal injections of 127 mg/kg LiCl (US) on 3 occasions. We then offered 23-h deprived rats NaSaccharin for 10 min/day to observe the course of recovery. Extinction occurred in three phases: static, dynamic, and asymptotic. During the static phase (mean = 9.6 days), rats consumed the CS at < 10% of their preconditioned rate. With dynamic recovery (6.0 days), they increased acceptance to > 80% of preconditioning levels. Finally, they achieved asymptote (3.1 days) at 100% acceptance. In Experiment 2, we used 8 additional conditioned rats and 8 unconditioned controls. We followed the same 1-bottle extinction procedure and, again, obtained 100% acceptance. Then we offered both NaSaccharin and water for 8 days at 23 h/day and monitored lick patterns every 6 s to determine taste preferences. The conditioned animals consumed less NaSaccharin than controls on Day 1, and less NaSaccharin as a percentage of total fluid as late as Day 3. For the last 5 days of 2-bottle preference testing, there were no significant differences between the groups with regard to 1. volume of NaSaccharin or water consumed, 2. percentage of total fluid taken as NaSaccharin, 3. consumption of each fluid associated with a meal or taken spontaneously, 4. intake during the light or dark periods, or 5. the characteristics of ingestion, including number of drinking bouts, duration of bouts, number of licks/bout, and rate of licking. Therefore, a robust CTA is subject to complete behavioral extinction.