Amygdala-prefrontal interactions and conditioned bradycardia in the rabbit

Damage to the amygdala or medial prefrontal cortex (mPFC) produces deficits in learned autonomic adjustments. Whether connections between these 2 structures are necessary for acquiring classically conditioned heart rate (HR) decelerations was studied. Connections between them were interrupted by unilateral lesions of the mPFC and amygdala, but on opposite sides of the brain. One experiment focused on the mPFC and amygdala central nucleus and a second on the mPFC and amygdala basolateral complex. Bilateral lesions of either structure disrupted the HR conditioned response. The response of the 2 crossed lesioned groups also was smaller than that of the sham-operated and unilateral lesioned groups, but significant conditioned stimulus-evoked bradycardia occurred in both, suggesting that although interactions between the amygdala and mPFC may normally occur during associative emotional responding, these connections are not necessary for the acquisition of conditioned bradycardia.

Lesions of the mediodorsal nucleus of the thalamus and classical eyeblink conditioning under less-than-optimal stimulus conditions: role of partial reinforcement and interstimulus interval

Rabbits received lesions of the mediodorsal nucleus of the thalamus (MD) or sham lesions and were subjected to classical eyeblink (EB) and heart rate (HR) conditioning. Separate groups of sham and lesioned animals received either 50% or 25% reinforcement with a periorbital shock unconditioned stimulus. Other groups received an interstimulus interval of either 1.0 or 1.5 s. Animals with MD lesions acquired the EB conditioned response (CR) more slowly than sham-lesioned animals with either the 1.5-s ISI or with the 25% reinforcement schedule. The lesions had no significant effect on the HR CR, however. Results suggest that information processed by MD is relayed to the prefrontal cortex and is required for somatomotor response selection under nonoptimal learning conditions.

Amygdala-prefrontal interactions and conditioned bradycardia in the rabbit

Damage to the amygdala or medial prefrontal cortex (mPFC) produces deficits in learned autonomic adjustments. Whether connections between these 2 structures are necessary for acquiring classically conditioned heart rate (HR) decelerations was studied. Connections between them were interrupted by unilateral lesions of the mPFC and amygdala, but on opposite sides of the brain. One experiment focused on the mPFC and amygdala central nucleus and a second on the mPFC and amygdala basolateral complex. Bilateral lesions of either structure disrupted the HR conditioned response. The response of the 2 crossed lesioned groups also was smaller than that of the sham-operated and unilateral lesioned groups, but significant conditioned stimulus-evoked bradycardia occurred in both, suggesting that although interactions between the amygdala and mPFC may normally occur during associative emotional responding, these connections are not necessary for the acquisition of conditioned bradycardia.

Lesions of the mediodorsal nucleus of the thalamus and classical eyeblink conditioning under less-than-optimal stimulus conditions: role of partial reinforcement and interstimulus interval

Rabbits received lesions of the mediodorsal nucleus of the thalamus (MD) or sham lesions and were subjected to classical eyeblink (EB) and heart rate (HR) conditioning. Separate groups of sham and lesioned animals received either 50% or 25% reinforcement with a periorbital shock unconditioned stimulus. Other groups received an interstimulus interval of either 1.0 or 1.5 s. Animals with MD lesions acquired the EB conditioned response (CR) more slowly than sham-lesioned animals with either the 1.5-s ISI or with the 25% reinforcement schedule. The lesions had no significant effect on the HR CR, however. Results suggest that information processed by MD is relayed to the prefrontal cortex and is required for somatomotor response selection under nonoptimal learning conditions.