Interaction between drug discriminative stimuli and exteroceptive, sensory signals.

Interactions between drug discriminative stimuli (based on 5.6 mg/kg and 10 mg/kg pentobarbital) and exteroceptive stimuli (visual and auditory) were studied in a T-maze. In three groups, visual stimuli (light vs. dark) were differentially paired with drug stimuli; the fourth group discriminated combinations of tonal frequencies (1 kHz or 10 kHz) and the presence or absence of pentobarbital. (10 mg/kg). In general, visual stimuli controlled choice behavior (left or right turn) to a greater extent than did the drug training stimuli, whereas the auditory stimuli exerted no apparent control over the pentobarbital stimulus in Group 4. Tests with doses higher than the training doses indicated augmented stimulus control by the drug dimension in two groups (Group 1, 10 mg/kg pentobarbital vs. saline; Group 2, 5.6 mg/kg vs. 10 mg/kg pentobarbital) but not in the third group (5.6 mg/kg pentobarbital vs. saline) in the "conflict" situation, that is, the exteroceptive conditions signaled one response whereas the drug stimulus signaled the opposite response. Discrimination training with only one of the stimulus dimensions resulted in stimulus control in the following order: 10 mg/kg vs. saline greater than 5.6 mg/kg vs. saline greater than 1 kHz vs. 10 kHz, results indicating that the auditory stimuli were of marginal significance. In conclusion, drugs can complete with exteroceptive, visual stimuli for associative strength.