Classical conditioning of heart rate discriminations using subcortical electrical stimulation as conditioned and unconditioned stimuli

Heart rate (HR) discriminations were classically conditioned in rabbits by having electrical stimulation of one medial geniculate or dorsal lateral geniculate body, but not the contralateral structure, immediately followed by hypothalamic, subthalamic or midbrain electrical stimulation. The major findings were that: (a) HR discriminations were elicited to midbrain or diencephalic unconditioned stimuli (US); (b) larger HR discriminations were conditioned to diencephalic than to midbrain US stimulation; (c) in both the midbrain and diencephalon, US electrode placements were found which either elicited accelerative or decelerative HR conditioning; and, (d) in diencephalic and midbrain reticular formation, but not midbrain central grey US sites, a strong positive relationship was found between accelerative HR responses and diffuse movement.