AROUSAL-INDUCED MODULATION OF MEMORY STORAGE PROCESSES IN HUMANS

We recently demonstrated in human subjects that muscle-tension-induced arousal can enhance later retention performance and that this effect is attenuated by P-adrenergic receptor antagonists. In that study, eac h subject established a baseline for muscle tension by squeezing a han d dynamometer for 30 s with maximum force. This may have served to ''p rime'' subsequent arousal produced by muscle tension. Two experiments were performed to address this issue. At the beginning of each experim ent, young adult subjects were asked to squeeze the hand dynamometer a t maximum effort either for 30 s (Prime) or for only 1 s (No prime). T hen, during the task, arousal was induced by having each subject exert a moderate amount of tension (25 to 50% of baseline maximum). In the first experiment, subjects were shown four consecutive lists of 20 hig hly imageable nouns, given immediate recall tests of each, and then gi ven a comprehensive recall and recognition test at the conclusion of t he experiment. Moderate arousal was induced once for each list (at enc oding, consolidation, or retrieval) or not at all for one list. The se quence of arousal induction was counterbalanced. Significant enhanceme nt of delayed recall was seen in the 30-s group for those lists in whi ch arousal was induced during the consolidation or retrieval period wi th no significant effects in the 1-s group. These results demonstrate that arousal can modulate memory consolidation when induced shortly af ter learning and that an initial priming event may affect the response to subsequent similar arousing events. In the second experiment, subj ects read paragraphs, some of which contained highlighted words (worki ng memory task); half of the subjects were given the 30-s procedure an d half the 1-s procedure. Only those subjects in the 30s group showed significant arousal-induced enhancement of delayed recognition of the highlighted words. Again, no significant effect on retention performan ce was seen in the group that squeezed the hand dynamometer for only 1 s during the priming period. Pulse data suggested that there may be s omewhat greater heart-rate reactivity in the 30s group. These findings suggest that memory modulation by arousal may be primed, or enhanced, by a relevant preliminary arousal event. (C) 1996 Academic Press, Inc .