Impact of Healthy Aging on Awareness and Fear Conditioning.

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Abstract
Fear conditioning has provided a useful model system for studying associative emotional learning, but the impact of healthy aging has gone relatively unexplored. The present study investigated fear conditioning across the adult life span in humans. A delay discrimination task was employed using visual conditioned stimuli and an auditory unconditioned stimulus. Awareness of the reinforcement contingen- cies was assessed in a postexperimental interview. Compared with young adult participants, middle-aged and older adults displayed reductions in unconditioned responding, discriminant conditioning, and contingency awareness. When awareness and overall arousability were taken into consideration, there were no residual effects of aging on conditioning. These results highlight the importance of considering the influence of declarative knowledge when interpreting age-associated changes in discriminative conditioned learning. Classical conditioning is a form of associative learning that depends on the functional integrity of two partially independent systems in the brain. An amygdala-based system is critical for the conditioning of emotional responses, largely assessed through fear conditioning procedures (Fendt & Fanselow, 1999; LaBar & LeDoux, 2001), whereas a cerebellar-based system is critical for the conditioning of somatomotor reflexes, largely assessed through eyeblink conditioning procedures (Steinmetz, 1998; Thompson, 1990). These systems perform similar functions across species, as electrophysiological and lesion studies initially conducted in ani- mals have been extended to human brain imaging and neurologic