Musical Emotion

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The neural substrates permitting the perception and expression of emotions through music are a relatively unexplored dimension of musical behaviour despite their obvious centrality to the enjoyment and importance of music. However, investigations into the perception of affect are under way.

Anne Blood, Robert Zatorre, and colleagues used PET to measure the correlation between CBF changes and the degree of dissonance or consonance (and unpleasantness or pleasantness) in musical excerpts constructed by altering the harmonic accompaniment of a novel tonal melody (Fig. 9A). Activation in the right parahippocampal gyrus and right inferior parietal lobe increased with increasing dissonance; that in portions of the orbitofrontal and subcallosal cingulate cortex increased with increasing consonance (Fig. 9B). Volunteers also rated the emotional quality of the excerpts along adjective pairs (e.g., pleasant vs unpleasant), two of which were known not to correlate with dissonance (happy vs sad). The fact that dissonance was associated with particular emotions (e.g., tense, unpleasant, irritated, and angry) and not others (Fig. 9A) suggests that the areas identified are involved in the perception of certain emotions, but not all.

The parahippocampal region is strongly and reciprocally connected with the amygdala, possibly involved in processing these emotions. CBF increases in the parahippocampal gyrus are also associated with unpleasant emotions in response to pictorial stimuli. Orbitofrontal and subcallosal cortex have been associated with emotional processing (e.g., the former with emotional disinhibition in monkeys following selective lesions, and deficits in emotional identification following subcallosal lesions in humans).

Blood and Zatorre measured the neural correlates of the experience of thrill during music perception. Though studied from a cognitive point of view by John Sloboda, this is probably the first study of the cortical and subcortical correlates of musical thrill. Subjects heard self-selected musical excerpts and made postscan ratings of subjective emotional intensity. Increased activity was associated with increasing intensity of thrill in the nucleus accumbens, midbrain, insula, thalamus, SMA, anterior cingulate, and orbi-tofrontal cortex. Decreasing activity was observed bilaterally in the amygdala and ventrolateral frontal cortex. These complex findings suggest the involvement of neural systems known to be associated with reward and arousal in the generation of musical thrill. Many of these areas have also been implicated in reward responses to other euphoria-inducing stimuli, both naturally occurring (e.g., food, sex) and artificial (e.g., cocaine, heroin). Thus music listening appears to serve some important biological function.

Peretz and colleagues noted that one of their auditory agnosia patients who no longer recognized any previously familiar melodies ("tune" agnosia) and could not detect pitch or rhythmic variations within novel melodies, utilize melodic contour or interval information, or sing, nevertheless reported that she still enjoyed music. Tests of her ability to discriminate the happy vs sad emotional valence of musical excerpts revealed that this ability was entirely intact. When the stimuli were presented in computer-synthesized versions rather than as recordings of live performances, emotional discrimination was unaffected, indicating that at least for these stimuli, expressive variations in timing and intensity were not significantly contributing to their emotional processing. The judgments were demonstrated to rely primarily on the mode (major/ minor) and tempo of the selection. This patient suffered sequential strokes affecting the left and right MCAs, which left extensive damage to almost the entirety of the left superior temporal gyrus (STG), the anterior third of the right STG, the middle and inferior temporal gyri, the left insula and frontal operculum, the right inferior and middle temporal gyri, and the left anterior parietal area. Though many hypotheses could be generated about the musical functions that might be impaired by such damage (e.g., singing and auditory-tonal working memory), it is interesting to note that most of the regions implicated by the PET studies of musical emotion described previously (with the exception of the left insula and left anterior parietal lobe) are spared. On the other hand, the emotional valence studied (happy vs sad) was not addressed by either of the activation studies. Clearly, much work remains to be done before the neural networks critical for the perception of specific categories of musically expressible emotions can be sorted out.

Figure 9 Consonant vs dissonant music perception. (A) (Top) Excerpts from the most consonant version (major triads; DissO) and the most dissonant version (13ths with flat 9ths; Diss5) of the musical stimuli presented during PET scanning. (Bottom) Line graphs demonstrating averaged subject ratings following scans for each of the six versions Diss0-Diss5. Note that dissonance was related to judgments of pleasantness/unpleasantness but not happiness/sadness. (B) Regions demonstrating significant rCBF correlations with dissonance level, parametrically varied from consonant to most dissonant in five steps by altering the harmonic accompaniment to a novel tonal melody. Correlations are shown as t-statistic images superimposed on corresponding averaged MRI scans. (a-c) Positive correlations in rCBF with increasing dissonance in (a) right parahippocampal gyrus in saggital section and (b) coronal section and (c) right precuneus. (d-f) Negative correlations with increasing dissonance (equivalent to positive correlations with increasing consonance) in (d) bilateral orbitofrontal cortex, (e) medial subcallosal cingulate in sagittal section, and (f) right frontopolar cortex (reproduced with permission from Blood et al., 1999).

Figure 9 Consonant vs dissonant music perception. (A) (Top) Excerpts from the most consonant version (major triads; DissO) and the most dissonant version (13ths with flat 9ths; Diss5) of the musical stimuli presented during PET scanning. (Bottom) Line graphs demonstrating averaged subject ratings following scans for each of the six versions Diss0-Diss5. Note that dissonance was related to judgments of pleasantness/unpleasantness but not happiness/sadness. (B) Regions demonstrating significant rCBF correlations with dissonance level, parametrically varied from consonant to most dissonant in five steps by altering the harmonic accompaniment to a novel tonal melody. Correlations are shown as t-statistic images superimposed on corresponding averaged MRI scans. (a-c) Positive correlations in rCBF with increasing dissonance in (a) right parahippocampal gyrus in saggital section and (b) coronal section and (c) right precuneus. (d-f) Negative correlations with increasing dissonance (equivalent to positive correlations with increasing consonance) in (d) bilateral orbitofrontal cortex, (e) medial subcallosal cingulate in sagittal section, and (f) right frontopolar cortex (reproduced with permission from Blood et al., 1999).

Although in the context of Peretz's task of emotional classification, expressive microvariations in timing, intensity, or pitch did not play a significant role, clearly in other contexts they are manipulated by skillful musicians to effectively communicate musical emotion. Examples of masters in this musical domain include musicians such as Mahalia Jackson, Maria Callas, Nusrat Fateh Ali Khan, and Claudio Arrau. Future studies may help to determine the neural processing consequences of both the sensory characteristics used to convey particular emotions (e.g., consonance/dissonance, tempo, harmonic structure, and intensity) and the particular emotions (e.g., happiness/sadness, pleasantness/unpleasantness, and thrill).

Finally, the neural substrates supporting the expression of musical emotion have yet to be explored (i.e., the motor control of the actions producing these expressive variations in musical sound and the perceptual processing of the emotional content of one's own performance). Though complex, to the degree that these expressive parameters can be quantified, neural correlates of their motor control may be sought.

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