Results
Behavioural Data
Figure 1 shows individual and average tension ratings for the Mendelssohn piece (version with dynamics). Pearson product–moment correlation coefficients between individual and average tension ratings of the different stimuli were high (M = 0.70; s.d. = 0.20). Overall, average tension profiles thus were in good correspondence with individual tension ratings. Likewise, within-participant correlations assessed by comparing tension ratings before and after scanning were high (Mendelssohn: M = 0.76; s.d. = 0.12; Mozart: M = 0.62; s.d. = 0.28) indicating that the subjective experience of musical tension remained relatively stable over time.
Mean valence ratings of the pieces (measured on a five-point scale) ranged between 3.47 and 4.38 (M = 4.00; s.d. = 0.34) showing that participants enjoyed listening to the pieces. Mean arousal ratings for the different pieces were moderate, ranging from 2.00 to 2.98 (M = 2.41, s.d. = 0.31).
Except for one participant who missed one of the four sine tones that had to be detected, all participants correctly detected the tones indicating that they attentively listened to the music stimuli during scanning.
fMRI Data
SPMs for the different contrasts and regressors are shown in Figure 2 (for details, see also Table 1). The contrast music > rating (Figure 2A) showed activation of bilateral supratemporal cortices. In each hemisphere, the maximum of this activation was located on Heschl's gyrus in the primary auditory cortex (right: 90% probability for Te1.0, left: 60% probability for Te1.0 according to Morosan et al., 2001), extending posteriorly along the lateral fissure into the planum temporale as well as anteriorly into the planum polare. Moreover, this contrast showed bilateral activation of the cornu ammonis (CA) of the hippocampal formation (right: 80% probability for CA, left: 70% probability for CA according to Amunts et al., 2005). Smaller clusters of activation for this contrast were found in the right central sulcus, left subgenual cingulate cortex, left caudate and left superior temporal sulcus (STS).
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Figure 2.
SPMs of different contrasts and regressors, (A)–(E) whole-brain analyses (P < 0.05, FWE-corrected) for the contrasts music > rating (A), loudness (B), tension (C), tension (versions with dynamics) > tension (versions without dynamics) (D), and tension increase > tension decrease (E). (F) ROI analysis for left and right amygdala for the contrast tension increase > tension decrease (P < 0.05, small-volume FWE-corrected). All images are shown in neurological convention.
Results of the loudness regressor (which, in contrast to the global music > rating contrast, specifically captured brain responses to loudness variations within music pieces) are shown in Figure 2B. This regressor revealed activations of Heschl's gyrus bilaterally (primary auditory cortices, right: 80% probability for Te1.0, left: 50% probability for Te1.0 according to Morosan et al., 2001) extending into adjacent auditory association cortex.
Figure 2C shows results of the tension regressor (pooled over versions with and without dynamics), indicating structures in which activity is related to felt musical tension. (Note that loudness was controlled for by including the loudness regressor in the model, and that, therefore, loudness did not contribute to the results of this tension analysis.) The tension regressor indicated a positive correlation with blood oxygen level-dependent (BOLD) signal changes in the left pars orbitalis of the IFG. No significant negative correlations were observed. To test whether the activation of the tension regressor differed between versions with and without dynamics, we also contrasted the tension regressor of original versions with versions with equalized MIDI velocity values (see Methods). For this contrast, i.e. tension (versions with dynamics) > tension (versions without dynamics), activations were found in left caudate nucleus (Figure 2D). The ROI analysis for the tension regressor in left and right amygdalae (guided by our hypotheses, see Introduction) did not result in any significant activations.
To investigate structures in which activity correlates specifically to the rise and decline of tension, we also compared epochs of increasing and decreasing tension (see blue and red areas in Figure 1). Figure 2E shows results of the contrast tension increase > tension decrease. This contrast yielded significant activations of Heschl's gyrus bilaterally (primary auditory cortices, right: 70% Te1.0, left: 70% Te1.1) extending in both hemispheres posteriorly into the planum temporale. Smaller foci of activation for this contrast were also found in right anterior middle frontal gyrus (MFG), right thalamus, right precentral sulcus and right cerebellum. The opposite contrast (tension decrease > tension increase) did not reveal any significant activations. An ROI analysis for the contrast tension increase > tension decrease in left and right amygdala indicated a significant activation of the right amygdala (MNI peak coordinate: 21 −4 −11; 80% probability for superficial group according to Amunts et al., 2005; P < 0.05, FWE-corrected on the peak level; cluster extent: six voxels; Figure 2F).
Functional Connectivity/Psychophysiological Interactions. To investigate whether there is a functional link between the brain regions associated with tension (in particular, the pars orbitalis and the amygdala), we also performed a post hoc functional connectivity/PPI analysis (Friston et al., 1997) in which we tested (i) which brain areas correlate to the activity in the peak voxels of the pars orbitalis and amygdala activations reported above (irrespective of subjectively experienced tension) and (ii) whether there is a psychophysiological interaction (PPI) with increasing or decreasing tension, i.e. in which brain areas the functional connectivity is modulated by tension (increasing vs decreasing).
The seed voxel in the left pars orbitalis (MNI coordinate: −39 38 −17) showed, among others, a significant functional connectivity (P < 0.05, FWE-corrected) with bilateral hippocampal and amygdalar regions (Figure 3). Conversely, the seed voxel in the right amygdala (MNI coordinate: 21 −4 −11) was functionally connected to the left pars orbitalis (for a complete list of significant activations from the functional connectivity analysis, see supplementary Table S1 http://scan.oxfordjournals.org/content/9/10/1515/suppl/DC1). The PPI analysis investigating in which regions functional connectivity is modulated by tension did not yield any significant results.
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Figure 3.
SPMs (P < 0.05, FWE-corrected) for the functional connectivity analysis with the peak voxel of the left pars orbitalis used as seed region (MNI coordinate: −39 38 −17). The maps show functional connectivity with bilateral hippocampal and amygdalar regions.