Epinephrine enhancement of human memory consolidation: Interaction with arousal at encoding
Introduction
Considerable evidence suggests that adrenergic hormones modulate the consolidation of long-term memory for experiences that induce their release. For example, post-training injection of adrenergic drugs or hormones enhances memory consolidation in many species (Cahill & McGaugh, 1998; Cahill, Prins, Weber, & McGaugh, 1994; Gold & van Buskirk, 1975; McGaugh, 2000; McGaugh, Cahill, & Roozendaal, 1996; Soetens, Casaer, D’Hooge, & Hueting, 1995). Despite this evidence, no demonstrations exist of enhanced memory consolidation in humans produced by adrenergic hormones, although enhanced consolidation in humans has been reported with post-learning administration of amphetamine (Soetens et al., 1995) glucose (Manning, Parsons, & Gold, 1992), and yohimbine (Southwick et al., 2002). The hypothesis that endogenous adrenergic hormones compose a necessary part of an endogenous memory-modulating system for emotionally arousing events in humans (Cahill & McGaugh, 1998) requires that, in appropriate conditions, these hormones be shown to enhance human long-term memory consolidation.
In this study, healthy humans received an intravenous infusion of epinephrine (EPI) after viewing a series of standardized slides. On the basis of a straightforward ‘time dependency’ view of memory consolidation (McGaugh, 1966), we predicted that EPI would most likely enhance memory for the slides viewed most recently before the infusion (recency effect). Other evidence suggests that drug-induced memory enhancement in humans can be restricted to the primacy portion of a series of items (Crow, 1979; Messier, Pierre, Desrochers, & Gravel, 1998). Therefore, we also examined the influence of EPI on retention of the initial slides viewed (primacy effect).
Section snippets
Materials and methods
Healthy volunteers (mean age (±SEM)=21.9±0.7 years, 22 male, 20 female). viewed a series of 21 standardized slides (Lang, Bradley, & Cuthbert, 1999) while seated comfortably before a viewing screen. Prior to slide viewing, each subject received an intravenous line in their left arm, and electrodes for continuous monitoring of heart rate (MP100 recording system, Biopac Instruments, Santa Barbara, CA) and pressure cuff on their right arm for blood pressure monitoring. The time between insertion
Results
Post-learning epinephrine administration significantly enhanced memory for the primacy slides (Fig. 1). A one-factor ANOVA of recall scores revealed a significant effect of drug condition [F(2,39)=3.74, p<.05]. Post-hoc t tests comparisons revealed a significant difference that subjects in the EPI 80 group recalled significantly more of the primacy slides that did subjects in the saline group [t(30)=−2.78,p=.009]. ANOVA of recall scores for the recency portion revealed no significant difference
Discussion
These findings support two primary conclusions. First, consistent with prior animal research, adrenergic hormones can produce retrograde enhancement of long-term memory in humans. Because epinephrine was administered after learning, its enhancing effect on memory cannot be attributed to actions on attentional, emotional, perceptual, or encoding processes during slide presentation. The findings thus provide new support for the hypothesis that adrenergic hormones, released by emotionally
Acknowledgments
Supported by NIMH Grant MH-57508 to L.C.
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