Sensory and associative effects of LSD in classical conditioning of rabbit (Oryctolagus cuniculus) nictitating membrane response.

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Abstract
The effects of LSD (30 nmol/kg) on the acquisition of the rabbit''s classically conditioned nictitating membrane response were studied. Experiment (exp) 1 revealed that LSD significantly enhanced the acquisition of conditioned responses [CR], and control groups receiving unpaired conditioned stimulus/unconditioned stimulus (CS/UCS) presentations served to identify LSD effect on learning. Whether LSD enhancing effects could have arisen from its altering the sensory processing of the CS and/or the UCS was determined. In exp 1, unconditioned response (UCR) amplitude to a 3 mA UCS was not significantly affected by LSD. Exp 2 revealed that LSD had no significant effect on the psychophysical functions relating UCS intensity to the frequency or amplitude of UCR and that the drug did not affect the UCS-intensity threshold for evoking UCR. Exp 3 revealed that LSD significantly enhanced the frequency of CR to an extended range of CS intensities in the psychophysical function relating CS intensity to CR frequency. LSD lowered the CS intensity threshold. The drug''s enhancement of the sensory processing of the CS was postulated to facilitate conditioning through both learning and performance mechanisms.