Modality and Prior Habituation as Critical Factors in Development of Rapid Discriminated Conditioned Suppression in Rats

Removing the bar in an appetitive lever-press task, the effects of number of CS-US pairings (1, 2, or 4), modality of the CS (2 tones vs light and tone) and prior CS habituation trials on the development of discriminated conditioned suppression were evaluated. Two or 4 CS-US pairings produced virtually a perfect discrimination with complete suppression to CS and little suppression to CS⁻. In addition there was a significant interaction of modality × shock, indicating that going from CS⁺ to CS⁻ had far less effect when the stimuli were in the same modality (T-T) than when modality changed (L-T). The effect of habituation training on suppression while not significant was in the expected direction, attenuating suppression to both CS⁺ and CS⁻.