کنترهای موسیقی آرامش بخش، تثبیت حافظه هیجانی را افزایش می دهد

Emotional events tend to be retained more strongly than other everyday occurrences, a phenomenon partially regulated by the neuromodulatory effects of arousal. Two experiments demonstrated the use of relaxing music as a means of reducing arousal levels, thereby challenging heightened long-term recall of an emotional story. In Experiment 1, participants (N = 84) viewed a slideshow, during which they listened to either an emotional or neutral narration, and were exposed to relaxing or no music. Retention was tested 1 week later via a forced choice recognition test. Retention for both the emotional content (Phase 2 of the story) and material presented immediately after the emotional content (Phase 3) was enhanced, when compared with retention for the neutral story. Relaxing music prevented the enhancement for material presented after the emotional content (Phase 3). Experiment 2 (N = 159) provided further support to the neuromodulatory effect of music by post-event presentation of both relaxing music and non-relaxing auditory stimuli (arousing music/background sound). Free recall of the story was assessed immediately afterwards and 1 week later. Relaxing music significantly reduced recall of the emotional story (Phase 2). The findings provide further insight into the capacity of relaxing music to attenuate the strength of emotional memory, offering support for the therapeutic use of music for such purposes.

Compared to everyday occurrences, memories of emotional events have been described as more vivid, distinct and robust to forgetting (Davidson et al., 2006, Heuer and Reisberg, 1990, Reisberg and Hertel, 2004 and Windmann and Kutas, 2001). Emphasis of potential threats and other significant stimuli is generally adaptive (McGaugh, 2000), but can also be detrimental to mental health. This is apparent in individuals suffering from the symptoms of Post Traumatic Stress Disorder (PTSD), where heightened retention of unwanted emotional material is a key symptom of this condition (Herman, 1992). Efforts to challenge heightened retention of unwanted emotional material are therefore of considerable clinical significance. While the underlying cause(s) of heightened emotional memory is still debated (Levine & Pizarro, 2004), there is now substantial evidence that emotional arousal acts a ‘neuromodulator’ of memory encoding or consolidation (Cahill and McGaugh, 1995 and Liu et al., 2008). An emotional event or stimulus that is significant and of influential capacity activates the Sympathetic Nervous System (SNS), which subsequently triggers the release of arousal hormones (such as cortisol, noradrenaline, and adrenaline) into the bloodstream, which then enhance memory by increasing noradrenergic activation within the amygdala (McGaugh, 1989 and McGaugh, 2004). In a pioneering study by Cahill and McGaugh (1995), participants were presented with a slideshow of 11 images accompanied by narratives of either an emotional or neutral story. Both conditions contained identical images with closely matched storylines. Arousal was manipulated by varying the accompanying narrative in the middle phase of the story (‘Phase 2’), where the emotional content was introduced. Subjective reports of arousal and long-term retention of the story were consistently higher among those who viewed the emotional, as compared to neutral, story (Arntz et al., 2005, Cahill and McGaugh, 1995, Hamann and Canli, 2004 and Quevedo et al., 2003). Furthermore, this discrepancy was most prominent during Phase 2 of the story. The consistency of images between conditions in this design excludes the possibility that differences in recall were due to variations to the intrinsic visual elements of the slides rather than narrative-induced changes in arousal (Christianson and Loftus, 1987 and Heuer and Reisberg, 1990). The facilitation of memory in these studies is typically attributed to increased emotional arousal which is intrinsic to the material being remembered (i.e., the emotional content of the story). However, the neuromodulatory process can extend beyond the initial formation of memory, in that arousal influences memory consolidation as well as memory encoding. For instance, intermediate doses of arousal hormones (adrenaline or noradrenaline) administered to young chicks up to 30 min after learning have been shown to enhance memory when tested several hours later (Crowe et al., 1990 and Gold and Van Buskirk, 1975). Emotionally arousing music has also been found to enhance long-term retention of a word list when presented 20 min after learning (Judde & Rickard, 2010). These findings suggest that the strength of a memory trace can be modulated by either exogenous or endogenous means of arousal presented during or after the learning phase (McGaugh, 2000). Importantly, the neuromodulatory process is bidirectional, implying that while increased arousal levels can enhance memory strength, reduced arousal levels can also attenuate recall (Cahill, Prins, Weber & McGaugh, 1994; Pitman et al., 2002). Cahill et al. (1994) demonstrated that enhanced recall among participants who viewed an emotionally arousing story can be prevented by the administration of the noradrenergic antagonist, propranolol. As this study eliminated the sedative influence of the drug as a contributing factor, the finding suggests that sources extrinsic to the emotional event or stimuli can reduce emotionally induced arousal and the enhanced memory that normally accompanies it. Recent studies (Pitman et al., 2002 and Vaiva et al., 2003) have further explored the therapeutic application of propranolol among the clinical population. Participants who were administered the drug tended to display fewer PTSD symptoms and later PTSD diagnoses in subsequent follow ups, when compared to those administered the placebo. While these studies support the potential of the therapeutic use of propranolol to reduce retention of unwanted emotional material and even the onset and severity of PTSD, pharmaceutical approaches have been contentious. Some have argued, for instance, that using a drug to erase or blunt unwanted emotional material may interfere with the normal process of emotional recovery, or falsify a true understanding and perception of reality (Dossey, 2006). While arousal-reducing music is also subject to such criticism, there is likely to be less community resistance to using music interventions in this context, perhaps because music is already part of everyday life for most people, whereas pharmaceutical manipulation of cognitive processes is not. The arousal-modulating capacity of music (see Baumgartner et al., 2006, Krumhansl, 1997 and Rickard, 2004) presents a plausible non-therapeutic alternative to the use of propranolol in attenuating the strength of unwanted memories. Indeed, relaxing music is often used to alleviate anxiety and stress-induced arousal responses, such as decreases in heart rate, blood pressure and skin conductance levels, in both clinical and non-clinical settings (Hodges, 2010, Knight and Rickard, 2001 and Pelletier, 2004). While it has been demonstrated that arousing music can increase emotionally induced arousal and subsequently enhance memory strength (Judde & Rickard, 2010), the neuromodulation theory also implies that relaxing music should also be capable of countering emotionally induced arousal and consolidation of emotional memory. The aim in the reported experiments was to explore whether music can challenge the heightened memory for emotionally arousing material. In Experiment 1, it was hypothesised that in the presence of relaxing music, the heightened retention scores for the emotionally arousing story would be significantly reduced (similar to those for the neutral story). In Experiment 2, it was hypothesised that this effect would also occur when music was presented after learning, and would not be generalised to non-relaxing or another auditory non-music condition.

The findings from these two experiments provide a novel demonstration of the effects of relaxing music on emotional memory. In addition, by introducing music into the experiment paradigm developed by Cahill and McGaugh (1995)after the learning phase, these data provided support for the neuromodulatory influence of relaxing music. While there is also evidence that emotional memory is modulated by cognitive factors such as attentiveness to, or distinctiveness of the emotional stimuli ( Burke et al., 1992 and Heuer and Reisberg, 1990), the use of extrinsic manipulation and presentation of stimuli after learning in this study implies that these factors are less likely to account for the effects in the current study. To our knowledge, this is the first demonstration, within a well-controlled experimental paradigm, that music can prevent heightened consolidation following exposure to aversive emotional stimuli. While the intensity of aversive experience induced by the emotional slideshow in no way simulates traumatic experience, studies examining the use of propranolol in attenuating the full intensity of traumatic emotional memories are to date scarce and limited by small sample sizes ( Pitman et al., 2002 and Vaiva et al., 2003). The current findings therefore provide some promise for the use of music as a potential treatment for decreasing the negative impact of emotionally laden information, including those associated with some forms of PTSD. Most significantly, they may offer a non-pharmaceutical means of modifying arousal levels in the aftermath of traumatic experiences, such that unwanted material does not become over-consolidated. Music exposure provides a simple and safe method of achieving this goal, and its efficacy even when presented shortly after the learned material makes it a practical therapeutic tool. Future research using different types of music with distinct populations may further clarify the capacity of music to prevent the potentially harmful physiological concomitants of stress reactions.