Fear-Potential Startle as a Model System for Analyzing Learning and Memory

Previous research has shown that the acoustic startle response, a simple reflex mediated by four synapses in the brainstorm and spinal cord, can be increased when elicited in the presence of a stimulus previously paired with a footshock. This fear-potentiated startle effect can be selectively blocked by drugs that decrease anxiety in humans as well as by lesions of the central nucleus of the amygdala, an area of the brain known to be critical for fear. This year it has been found that a footshocks by themselves cause a marked increase in the startle reflex which appears to result from an activation of the central nucleus of the amygdala b low level electrical stimulation of the central nucleus of the amygdala increases the acoustic startle reflex with a transit time of about 5 msec from the amygdala to the acoustic startle circuit c a direct anatomical connection exists between the central nucleus of the nucleus of the amygdala and the acoustic startle pathway and d lesions at several points along this pathway prevent a fear stimulus from potentiating the startle reflex.