Conditioning, awareness, and the hippocampus

For the past 50 years, psychologists have wrestled with questions regarding the relationship between conscious awareness and human conditioned behavio r. A recent proposal that the hippocampus mediates awareness during trace c onditioning (Clark, Squire, Science 1998;280:77-81) has extended the awaren ess-conditioning debate to the neuroscience arena. In the following comment ary, we raise specific theoretical and methodological issues regarding the Clark and Squire study and place their finding into a broader context. Thro ughout our discussion, we consider the difficulties in assessing subjective awareness, the importance of establishing necessary and sufficient conditi ons for cognitive mediation effects, the influence of conditioned response modality, and the nature of hippocampal requirements across conditioning pr otocols. It is clear that trace eyeblink conditioning is a hippocampal-depe ndent task, but whether awareness is a necessary component of trace conditi oning is not definitively proven. We propose that future functional neuroim aging studies and behavioral experiments using on-line measures of awarenes s may help clarify the relationship among classical conditioning, awareness , and the hippocampus. Hippocampus 1998;8:620-626. (C) 1998 Wiley-Liss, Inc .