Cortical spreading depression and conditioned taste aversion: an attempt to resolve a controversy

The claim (Winn, Todd, & Elias, Behav. Biol. 19, 55-63 (1977) ) that cortical spreading depression (CSD) can serve as US in the conditioned taste-aversion (CTA) paradigm was experimentally examined. Rats given 15-min access to novel 0.1% sodium saccharin (CS) followed by ip NaCl and bilateral or unilateral CSD (US) displayed similar saccharin preference (54%) as the sham-CSD-treated controls in a multiple-bottle retention test. Rats receiving ip LiCl (0.15 M, 2% body weight) and sham CSD as the US showed marked saccharin aversion. It is concluded that CSD does not elicit CTA and that some claims to the contrary can perhaps be ascribed to CSD-induced disruption of attenuation of neophobia.     

Modulation of a conditioned eyeblink response by a putative emotive stimulus conditioned with hindleg shock

Two experiments with rabbits showed that the differential modulation of a conditioned eyeblink response (CR) by 30-s auditory stimuli previously paired with shock was independent of the locus of shock application. In Experiment 1, the modulation occurred when the CR was trained with paraorbital shock and the 30-s stimuli were trained with either hindleg or paraorbital shock. Experiment 2 replicated the observed adequacy of hindleg shock for modulation training, under 2 different conditions of eyeblink conditioning. The data, along with the findings that the same 30-s stimuli similarly facilitate the unconditioned eyeblink and the airpuff-elicited startle response (Brandon, Bombace, Falls & Wagner, 1991), were viewed as supporting the notion that the CR-modulation is dependent upon a conditioned fear response elicited by the 30-s cues (Wagner & Brandon, 1989).     

Retention of a classically conditioned reflex response in spinal cat

Retention of classically conditioned flexion reflex facilitation was examined in unanesthetized, decerebrate, acute spinal cats. Flexion reflex facilitation, recorded from the tibialis anterior muscle, was obtained by pairing saphenous nerve stimulation (the conditioned stimulus) with superficial peroneal nerve stimulation (the unconditioned stimulus). The flexion reflex declined in control animals receiving the same number of nerve stimuli over the same time span, but in an explicitly unpaired sequence. To investigate retention, conditioned stimuli were presented at 5-min intervals following acquisition for a 2 1/2-h period. During this time a significant difference between conditioning and control groups was maintained even to the last trial, with no indication that the difference was subsiding over time. The results support the possibility that a classical conditioning paradigm applied to the spinal cord can induce alterations in spinal reflexes of long duration. Furthermore, the results appear to rule out post-tetanic potentiation as a mechanism producing the observed long-term effects.