Effect of midazolam on memory: a study of process dissociation procedure and functional magnetic resonance imaging

To assess the effects of midazolam on explicit and implicit memories, 12 volunteers were randomly divided into the two groups: one with an Observer's Assessment of Alertness/Sedation score of 3 (mild sedation) and one with a score of 1 (deep sedation). Blood oxygen-level-dependent functional magnetic resonance imaging was measured before and during an auditory stimulus, then with midazolam sedation, and then during a second auditory stimulus with continuous midazolam sedation. After 4 h, explicit and implicit memories were assessed. There was no evidence of explicit memory at the two levels of midazolam sedation. Implicit memory was retained at a mild level of midazolam sedation but absent at a deep level of midazolam sedation. At a mild level of midazolam sedation, activation of all brain areas by auditory stimulus (as measured by functional magnetic resonance imaging) was uninhibited. However, a deep level of midazolam sedation depressed activation of the superior temporal gyrus by auditory stimulus. We conclude that midazolam does not abolish implicit memory at a mild sedation level, but can abolish both explicit and implicit memories at a deep sedation level. The superior temporal gyrus may be one of the target areas.