hang on: so IMPROVISATION of melody results from DEACTIVATION of the rTPJ ? For context:
rTPJ: “The right temporoparietal junction (rTPJ) is frequently associated with different capacities that to shift attention to unexpected stimuli (reorienting of attention) and to understand others’ (false) mental state [theory of mind (ToM), typically represented by false belief tasks]”
“While we had hypothesized that differences would likely be found in the frontal regions involved in generation and selection of novel motor sequences (e.g., inferior frontal gyrus, anterior cingulate cortex, dorsal premotor cortex), we did not predict that the main difference would be in degree of deactivation of a parietal region, nor that the difference would be for melodic improvisation but not rhythmic improvisation, nor that the frontal areas listed above would show no differences between groups. In what follows, after reviewing relevant literature on the purported role of the rTPJ and its deactivation in various cognitive tasks, we propose an explanation for the relevance of expertise-related deactivation of this region during improvisation. We then discuss possible explanations for the lack of group differences during rhythmic improvisation and in the frontal areas seen in our previous study of musicians alone.
The rTPJ is thought to be part of a ventral attentional network for bottom-up stimulus-driven processing (for reviews, see Corbetta and Shulman, 2002; Corbetta et al., 2008). Brain imaging results have supported the hypothesis that this region is important for reorienting attention when behaviorally relevant stimuli in any sensory modality are detected (Downar et al., 2000, 2001, and 2002; Kincade et al., 2005; Serences et al., 2005; Corbetta and Shulman, 2002; Corbetta et al., 2008). Deactivation of this region has been postulated to occur in response to top-down signals during goal-driven behavior so as to inhibit attentional shifts toward task-irrelevant stimuli that could cause decrements in performance (Shulman et al., 2003; Todd et al., 2005; for a review, see Corbetta et al., 2008). These top-down signals are thought to serve a filtering function, allowing only taskrelevant stimuli to activate the rTPJ, and preventing a reorienting to task-irrelevant stimuli (Corbetta et al., 2008). In support of such theories of rTPJ function, increasing deactivation of this region has been found to correlate with more successful task performance in target detection (Shulman et al., 2007) and visual short-term memory (Chee and Chuah, 2007), as well as faster reaction times when processing large numbers of objects as opposed to smaller numbers (Ansari et al., 2007).
Although deactivation of the rTPJ has been correlated with improved task performance in these contexts, the deactivation of this region as a function of expertise revealed in the present paper is, to our knowledge, a novel finding. The deactivation of the rTPJ cannot be critical for the invention of novel motor sequences: despite a lack of deactivation in this region, nonmusicians achieved a level of novelty in melodic improvisation equivalent to that of the musician group, as evidenced by the lack of difference between the two groups in the percent of unique melodic sequences generated during the melodic improvisation conditions. In light of the prior work on the rTPJ reviewed above, we propose two related (and not mutually exclusive) possibilities for why musicians would demonstrate substantial deactivation of this region during improvisation while nonmusicians do not show any significant change in activity: training-induced changes in goal-directed attention and/or shifts toward a more topdown cognitive strategy. When improvising, musicians are in a goal-driven state of invention, and, at least in the case of our experiment, the pursuit of novelty. It is thus important for their attention not to be distracted by irrelevant stimuli (e.g., in this experiment, scanner noise, errors in intended performance, etc.). The deactivation of the rTPJ region in experienced musicians suggests that their expertise may allow them to enter a more focused attentional state during performance of this task. Moreover, while the deactivations in the rTPJ in the musician group were statistically significant only for conditions involving melodic improvisation, visual inspection of Fig. 2 shows that a trend toward deactivation is seen even with rhythmic improvisation alone (Patterns/Rhythmic Improvisation) and to a lesser degree, with no improvisation at all (Patterns/Metronome). This suggests that musicians are entering a different state of attentional focus than nonmusicians as soon as they engage in even the simple act of playing, and that this effect is particularly heightened during melodic improvisation. Widespread deactivations during the performance of a previously memorized piece of music have been theorized to play a similar role in that context (Parsons et al., 2005). Sustained attention is indeed thought to be a critical cognitive process for creativity (Dietrich, 2004). Thus, one interpretation of the present finding is that musicians may have been more focused and/or goal driven in their task performance, whereas nonmusicians, because of lack of experience, may have been less so.
Beyond the general possibility of a more focused goal-driven attentional state, a more specific potential interpretation of the musicians’ deactivation of the rTPJ during improvisation is that they strategized in a more top-down fashion, conceiving of and/or planning their improvised melodies as 5-note groups, and thus inhibiting any sort of stimulus-driven response to what they played while they planned their next improvised sequence. Nonmusicians, lacking musical experience, may have been more dependent on stimulus-driven information (i.e., auditory and sensory feedback) during melodic improvisation. This is consistent with the proposal of a recent fMRI study in which musicians’ and nonmusicians’ brain activity were compared during tasks of rhythmic synchronization, showing overlapping but distinct neural substrates between the two groups (Chen et al., 2008). These authors postulate a model in which musicians use a top-down strategy based on their prior knowledge of musical structure, whereas nonmusicians, without such knowledge, are relegated to bottom-up processing. Our results may indicate a similar training-induced shift toward a top-down processing strategy in improvisation. Such a strategy has also been described in a recent EEG study of the imagery of improvised dance in professionals versus novices (Fink et al., 2009b). In this study, increased alpha synchronization in right temporoparietal and parietooccipital areas in professional dancers as compared to novices was revealed, which the authors interpreted as reflecting top-down inhibition to prevent interference from task-irrelevant information during creative thinking. Top-down inhibition of stimulus-driven attention is also thought to correlate with novel idea generation during creative problem solving in the verbal domain (Fink et al., 2009a). Thus, such top-down inhibition may be an important component of creative thought across domains
from Expertise-related deactivation of the right temporoparietal junction during musical improvisation