Effect of hippocampal lesions on heart-rate during classical fear conditioning

Of 22 male albino rats, eight received bilateral lesions at three levels of the hippocampus, six received bilateral lesions of the amygdaloid complex and eight served as unoperated controls. Each rat received 30 fear conditioning trials in which shock was paired with a CS, either light or a tone. After every tenth trial there was a test trial in which heart-beats were recorded. The typical heart-rate response of controls was deceleration-acceleration while for hippocampal lesioned rats it was short latency acceleration. The results were interpreted in terms of two heart-rate theories.