Effect of the duration of a conditioned stimulus on component recognition in binary taste mixtures in rats

The aim of this behavioral study was to investigate the duration of a conditioned stimulus (CS-duration) necessary for rats to recognize the components of a binary taste mixture in a conditioned taste aversion (CTA) paradigm as well as the relationship between CS-duration and their spontaneous recovery.

The experimental rats were categorized under conditioned and control groups and further divided into three groups according to the CS-duration: 10, 30, and 60 s. As the test stimuli, a mixture of 100 mM sucrose (S) + 30 μM quinine hydrochloride (Q) and its components were used.

On day 1 of the CTA test, the number of licks (NL) for S + Q and S in all conditioned groups was significantly lower than that of the control group presented with CS for 60 s (CON-60), which was the representative control group determined by the initial CTA test. For Q, there was no significant difference between NL of the CTA group presented with CS for 10 s and that of CON-60; however, NL in the other two CTA groups, i.e., CTA-30 and CTA-60, was significantly lower than that of CON-60. When the rats were presented with a shorter CS-duration, they showed spontaneous recovery earlier depending on the CS-duration.

These results suggest that rats can recognize a binary taste mixture and its components using a CS-duration of more than 30 s and that spontaneous recovery from CTA learning depends on the CS- duration.