A specific feature of the perceptually based music memory system is that the stored information is relatively abstract (compared with that in semantic memory), allowing recognition despite changes in instrumentation, loudness, tempo or register. Lesion studies and recent brain imaging studies [19-21] have shown that this perceptual memory system is located bilaterally in the auditory cortex (including the supramarginal gyrus). In addition, the inferior frontal and inferior temporal brain areas have been shown to be important in recognizing familiar tunes. To determine where other kinds of musical memory are stored in the brain, however, a distinction needs to be made between an episodic and a semantic musical memory system. Episodic memory for musical information is defined by Platel and colleagues [5] as "the capacity to recognize a musical excerpt (whether familiar or not) for which the spatiotemporal context surrounding its former encounter (i.e., when, where, and how) can be recalled". Semantic memory allows us to identify familiar songs or melodies by naming the tune or by humming or whistling the subsequent notes of a melody. It is thought that musical semantic memory may represent a musical lexicon, which is different from a verbal lexicon, even though there are certainly strong links between them (see above). On the basis of a high-resolution positron emission tomography study, Platel and colleagues [5] delineated different brain networks involved in processing semantic and episodic memory. For episodic musical memory they found increases in cerebral blood flow bilaterally in the middle and superior frontal gyrus region (with a left-sided preponderance) and the precuneus, whereas for semantic musical memory there was a blood flow increase bilaterally in the medial and the orbitofrontal cortex, the left angular gyrus, and the left anterior part of the middle temporal cortex. From these findings one can conclude that these two different musical memory systems have a different neural representation. It is interesting to note that these brain areas partly overlap with verbal semantic and episodic memory systems.
Emotion, music and memory
Another recent study [22] examined the memories and emotions that are often evoked when hearing musical pieces from one's past. In this experiment, subjects were presented with a large set of short musical excerpts (not longer than 30 seconds per excerpt) of past popular songs. Using a set of newly designed questionnaires, the authors found that, on average, 30% of the presented songs evoked autobiographical memories. In addition, most of the songs also evoked various strong emotions, which were mainly positive ones such as nostalgia. These results are consistent with the broader literature (reviewed in [23]) in which enhanced recall is observed for both positively valenced (intrinsically pleasant) and arousing (stimulating) events. Thus, positive emotions and high arousal levels that are associated with specific events act as a memory enhancer for these particular events. In the context of associative memory models, this memory-enhancing effect of emotions and arousal can be explained as a strengthening of the associations between the memories due to strong emotions and to arousal.
Until recently however, no study has explicitly examined whether emotional valence or arousal are correlated with musical memory. In a recent paper published in BMC Neuroscience, Eschrich and colleagues [6] investigate whether musical pieces that induce high arousal and very positive valence are remembered better by non-musicians than unarousing and emotionally neutral musical pieces. To examine these questions the authors designed a behavioral memory experiment composed of two sessions. In the first session (the encoding phase) the subjects were exposed to 40 musical pieces, each lasting 20–30 seconds. One week later, in the recognition phase, participants listened to the 40 old musical excerpts randomly interspersed with 40 new excerpts and were asked to make a decision about whether each one was old or new, and to indicate the arousal level and emotional valence of the pieces. The musical stimuli were selected from a larger data pool by musically trained raters and comprised symphonic film music by various composers. From the old/new decisions of the participating subjects, the researchers calculated recognition scores and demonstrated that musical pieces that were rated as very positive were recognized significantly better than those rated as less positive. Arousal ratings were not predictive for recognition performance, meaning that only emotional valence is related to musical memory [6].
A further part of this experiment [16] was designed to assess whether different psychological conditions present during the encoding phase might have an influence on musical memory performance. For this, the authors divided the subject sample into two groups: one required to judge valence during encoding (the emotion group) and the other required to estimate the length and general loudness of each musical stimulus (the time-estimation group). The two groups did not differ in their recognition scores. It is interesting that the time-estimation group, despite not concentrating on the emotions during the first encoding session, showed the same recognition performance as the emotion group. This shows that emotion is automatically evoked by the musical pieces and inevitably influences recognition, even when it is not focused on.
In summary, the study by Eschrich and colleagues [6] is consistent with the rest of the literature on emotion as a memory enhancer. The novel aspect of this study, however, is the finding that musical memory is strongly related to the rated attractiveness and not to the experienced arousal of the musical piece. Thus, emotion enhances not only memories for verbal or pictorial material, as summarized by Buchanan [23], but also for musical pieces. This study [6] also provides additional support for a tremendous role of music in building our autobiographical memories. Emotional music we have heard at specific periods of our life is strongly linked to our autobiographical memory and thus is closely involved in forming our view about our own self. In this respect it is interesting to note that listening to music is not only accompanied by blood flow increases in brain areas known to be involved in generating and controlling emotions [12,13], but it is also accompanied by a general increase and change of brain activation within a distributed network comprising many brain areas and the peripheral nervous system [11,24-27]. Thus, listening to music (even when we listen passively) activates many psychological functions (emotion, memory, attention, imagery and so on) located in a distributed, overlapping brain network.
If music has such a strong influence on emotions and our cognitive system, this raises the question of whether the memory-enhancing effect of emotional music can be used to enhance cognitive performance in general and in clinical settings. In a single-blind, randomized and controlled study, Särkämö et al. [28] examined whether everyday music listening can facilitate the recovery of cognitive functions and mood after a stroke. The results of this study revealed that recovery of verbal memory and focused attention improved significantly in the group of patients who listened to their favorite music on a daily basis compared with the patients who listened to audio books or received no listening material (control group). Besides the improvement in cognitive functions, there was also a substantial mood improvement in the patients who listened to music (they were less depressed and less confused) compared with the control group.
These studies and especially the study by Eschrich and colleagues [6] support the tremendous influence of music on our emotional and cognitive system. Music automatically awakes us, arouses us and engenders specific emotions in us, which in turn modulates and controls many cognitive functions.