title: Distinct contributions of the amygdala and hippocampus to fear expression.
abstract: The present study attempted to distinguish the independent contributions of the amygdala and hippocampus to fear expression. Rhesus monkeys (Macaca mulatta) with bilateral excitotoxic amygdala lesions (n = 4), bilateral excitotoxic hippocampal lesions (n = 8) and unoperated controls (n = 9) were allowed to reach over a neutral junk object or fear-provoking stimulus (i.e., a rubber snake or a jumping rubber spider) to retrieve a food reward. Monkeys were exposed to each stimulus for 30 s. On each trial we recorded the monkey's latency to retrieve the food reward and scored their whole-body reactions to the object. Confirming previous work we found that, relative to controls, both operated groups showed shorter food-retrieval latencies and exhibited fewer defensive and more approach behaviors when exposed to the fear-provoking stimuli. However, only monkeys with amygdala lesions showed an abnormal, excessive visual interest in the snake and spider. By contrast, monkeys with hippocampal lesions displayed behaviors that were unrelated to the presence of the fear stimuli, thereby indicating a lack of interest in, and emotional reactivity towards, the snake and spider. These data show that the hippocampus and amygdala contribute independently to the overall expression of defensive responses.
authors.affiliation: Neurobiology of Learning and Memory Section, Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA. yogita.chudasama@mcgill.ca
authors.forename: Yogita
authors.initials: Y
authors.lastname: Chudasama
authors.forename: Alicia
authors.initials: A
authors.lastname: Izquierdo
authors.forename: Elisabeth A
authors.initials: EA
authors.lastname: Murray
mesh_terms: D000679:Amygdala / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D005133:Eye Movements / Q000502:physiology; D005239:Fear / Q000502:physiology*; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007051:Ibotenic Acid / Q000633:toxicity; D008253:Macaca mulatta; D008297:Male; D009043:Motor Activity / Q000502:physiology; D009483:Neuropsychological Tests; D009498:Neurotoxins / Q000633:toxicity; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time; D013647:Task Performance and Analysis
chemical_list: D009498:Neurotoxins; D007051:Ibotenic Acid