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Experimental evidence has linked increased arousal to enhanced memory retention. There is also evidence that procedures reducing arousal, i.e., mental relaxation, might improve memory, but conflicting results have been reported. To clarify this issue, we studied the effects of a single session of relaxation training on incidental visual long-term memory. Thirty-two relaxation-naive subjects viewed 280 slides without being told that there would be subsequent memory testing. Afterwards, subjects listened to a 12 min relaxation tape; 16 subjects relaxed by following the instructions (relaxation group), and the other 16 subjects pressed a button whenever a body part was mentioned (control group). While listening to the relaxation tape, high frequency heart rate variability (HRV) was greater and low frequency HRV was lower in the relaxation group, implying effective relaxation and increasing parasympathetic activation. The relaxation group had superior memory retention 4 weeks later (p=.004), indicating enhancement of long-term memory performance. This effect could not be explained by retroactive interference experienced in the control group because short-term memory performance immediately after the tape was slightly better in the control group. Retention of materials acquired after the relaxation session remained unaffected, suggesting relaxation has retrograde effects on memory consolidation. Our data demonstrate a favorable influence of relaxation on at least this aspect of learning. Our data also extend previous knowledge on the beneficial effects of ascending parasympathetic stimulation on memory retention in that enhanced long-term memory consolidation may also occur in the presence of central and descending parasympathetic activation triggered by willful psychomotor activity.

Increased arousal, stress hormones, and sympathetic nervous system (SNS) activation have been shown to favor memory retention (Cahill & McGaugh, 1998). Relaxation (involving directed psychomotor techniques) is known to reduce arousal and shift autonomic nervous system function toward increased parasympathetic nervous system (PNS) and reduced SNS activity (Sakakibara, Takeuchi, & Hayano, 1994). This raises the possibility that relaxation might degrade memory processes. However, the existing literature on relaxation induced memory effects is equivocal. Short-term memory has been shown to improve after relaxation in some (Krampen, 1997; Legostaev, 1996), but not all (Rankin, Gilner, & Gfeller, 1993) studies. It has also been suggested that incidental memory improves but non-incidental long-term memory remains unaffected by relaxation (Lindsay & Morrison, 1996). Thus, the impact of relaxation on human memory, especially on incidental long-term memory, remains unclear. In the present study, we examined whether a single brief relaxation session would improve short-term and long-term memory retention in healthy adult humans. Relaxation training is known to increase heart rate variability (HRV) (Sakakibara et al., 1994). Thus, we also assessed HRV, as well as self-reported relaxation, as measures of the effectiveness of the relaxation procedure.