Neurophysiological theory of Kamin blocking in fear conditioning.

Kamin blocking in fear conditioning is thought to reflect diminished processing of the unconditional stimulus (US) in the presence of a conditional stimulus (CS+) that was previously paired with this US. According to Fanselow's (1998) hypothesis, the CS+ drives output from the amygdala that ultimately produces analgesia by causing opiate release onto afferent pain circuits. This hypothesis was explored quantitatively through neurophysiological simulations. The results suggest that opiate-mediated, negative-feedback control of US processing is too slow for efficient blocking of cue conditioning. The reason is that conditioning-produced synaptic modifications can be induced before the opiate-mediated inhibition has any substantial effect on US processing. The results suggest the existence of an additional, faster-acting, inhibitory neurotransmitter in the blocking circuit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)