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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Different Fear-Conditioned Behaviors Mediated By Different Brain Sites ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ WESTPORT, Jul 24 (Reuters) - The amygdala is known to be involved in responses to fear. Now, in studies in rats, British researchers have discovered that Pavlovian fear-conditioned reflexive responses and voluntary avoidance responses are independently mediated by two separate nuclei within the amygdala. Today in Nature, Dr. Barry J. Everitt and colleagues at the University of Cambridge, UK, explain that they first trained the rats to press on two levers for food. Then they taught the animals to recognize an auditory signal that would precede a mild footshock on one of two levers. According to Dr. Everitt, rats with lesions of their central amygdaloid nucleus had impaired conditioned responses to fear stimuli but were still able to select the lever that did not produce the shock, thereby avoiding the fearful stimulus. Rats with lesions of the basolateral amygdala, in contrast, had normal reflexive reactions, but these animals were not able to avoid the fear stimulus by correct choice of lever. "This double dissociation demonstrates that distinct neural systems involving separate amygdaloid nuclei mediate different types of conditioned fear behavior," Dr. Everitt writes. The investigators suggest that the findings have direct implications for the understanding of anxiety and emotional behaviors. "Theories of amygdala function should take into account the roles of discrete amygdala subsystems in controlling different components of integrated emotional responses." Nature 1997;388:377-380. Westport Newsroom 203 319 2700 Copyright =A9 1997 Reuters Limited. <http://www.reutershealth.com/news/docs/199707/19970724sca.html> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [log in to unmask]