Is priming during anesthesia unconscious?

General anesthesia provides an alternative to typical laboratory paradigms for investigating implicit learning. We assess the evidence that a simple type of learning--priming--can occur without consciousness. Although priming has been shown to be a small but persistent phenomenon in surgical patients (Merikle & Daneman, 1996) there is reason to question whether it occurs implicitly due to problems in detecting awareness using typical clinical signs. This paper reviews the published studies on priming during anesthesia that have included a measure of awareness or of anesthetic depth. We conclude that perceptual priming, but not conceptual priming, takes place in the absence of conscious awareness.