Investigations of hypesthesia: using anesthetics to explore relationships between consciousness, learning, and memory

This paper discusses the ways in which anesthetic agents can be used to investigate the role of awareness in learning and memory. It reviews research into learning during light, subclinical anesthesia, termed hypesthesia. This research suggests that the effects of anesthetics on implicit and explicit memory are roughly comparable, although implicit memory for simple stimuli may resist the effects of very low doses of anesthetic. In addition, this paper reports experimental data demonstrating that long-term retention of information is prevented by doses of anesthetic that are low enough to permit awareness and even shortterm memory of auditory stimuli. Overall, these findings are consistent with the hypothesis (e.g., Caseley-Rondi, 1996) that frontal lobe function is particularly sensitive to anesthetics. They raise theoretical and practical questions about the necessity of consciousness for learning and about interpretation of the evidence for learning during surgery under general anesthesia.