Our results strongly implicate a distinctive pattern of changes in prefrontal cortical activity that underlies the process of spontaneous musical composition. Our data indicate that spontaneous improvisation, independent of the degree of musical complexity, is characterized by widespread deactivation of lateral portions of the prefrontal cortex together with focal activation of medial prefrontal cortex. This unique pattern may offer insights into cognitive dissociations that may be intrinsic to the creative process: the innovative, internally motivated production of novel material (at once rule based and highly structured) that can apparently occur outside of conscious awareness and beyond volitional control.
In jazz music, improvisation is considered to be a highly individual expression of an artist's own musical viewpoint 
. The association of MPFC activity with the production of autobiographical narrative 
is germane in this context, and as such, one could argue that improvisation is a way of expressing one's own musical voice or story 
. In this sense, activity of the MPFC during improvisation is also consistent with an emerging view that the region plays a role in the neural instantiation of self, organizing internally motivated, self-generated, and stimulus-independent behaviors 
. The portion of the MPFC that was selectively activated during improvisation, the frontal polar cortex (Brodmann Area 10), remains poorly understood but appears to serve a broad-based integrative function, combining multiple cognitive operations in the pursuit of higher behavioral goals 
, in particular adopting and utilizing rule sets that guide ongoing behavior 
and maintaining an overriding set of intentions while executing a series of diverse behavioral subroutines 
. All of these functions are necessarily required during the task of improvisation.
In comparison, the lateral prefrontal regions (LOFC and DLPFC), which were deactivated during improvisation, are thought to provide a cognitive framework within which goal-directed behaviors are consciously monitored, evaluated and corrected. The LOFC may be involved in assessing whether such behaviors conform to social demands, exerting inhibitory control over inappropriate or maladaptive performance 
. The DLPFC, on the other hand, is thought to be responsible for planning, stepwise implementation and on-line adjustment of behavioral sequences that require retention of preceding steps in working memory 
. The DLPFC is active, for example, during effortful problem-solving, conscious self-monitoring and focused attention 
In light of these distinct roles, we believe that the dissociation of activity in MPFC and LOFC/DLPFC observed here during improvisation is highly meaningful. If increased activity in the MPFC serves as an index of internally motivated behavior, concomitant decreases in the LOF and DLPFC suggest that self-generated behaviors (such as improvisation) occur here in the absence of the context typically provided by the lateral prefrontal regions. Whereas activation of the lateral regions appears to support self-monitoring and focused attention, deactivation may be associated with defocused, free-floating attention that permits spontaneous unplanned associations, and sudden insights or realizations 
. The idea that spontaneous composition relies to some degree on intuition, the “ability to arrive at a solution without reasoning” 
, may be consistent with the dissociated pattern of prefrontal activity we observed. That is, creative intuition may operate when an attenuated DLPFC no longer regulates the contents of consciousness, allowing unfiltered, unconscious, or random thoughts and sensations to emerge. Therefore, rather than operating in accordance with conscious strategies and expectations, musical improvisation may be associated with behaviors that conform to rules implemented by the MPFC outside of conscious awareness 
. Indeed, in other domains it has been shown that focused attention and conscious self-monitoring can inhibit spontaneity and impair performance 
. In short, musical creativity vis-à-vis improvisation may be a result of the combination of intentional, internally generated self-expression (MPFC-mediated) with the suspension of self-monitoring and related processes (LOFC- and DLPFC-mediated) that typically regulate conscious control of goal-directed, predictable, or planned actions.
While the results of some previous studies 
suggest that decreased activity in the DLPFC may indicate a reduction in working memory demands, we feel that this is unlikely here (indeed, it could be argued that improvisation places a greater demand upon working memory mechanisms than the routinized musical performance characterizing our control conditions). Since we minimized working memory demands in both paradigms–utilizing over-learned control tasks as well as experimental conditions in which subjects were relatively free to improvise–we suggest that attenuation of activity in the DLPFC in the present instance more likely reflects a reduction in the prefrontal mechanisms outlined above.
It has also been suggested that deactivation of the lateral prefrontal regions represents the primary physiologic change responsible for altered states of consciousness such as hypnosis, meditation or even daydreaming 
. This is interesting in that jazz improvisation, as well as many other types of creative activity, have been proposed to take place in an analogously altered state of mind 
. Moreover, a comparable dissociated pattern of activity in prefrontal regions has been reported to occur during REM sleep 
, a provocative finding when one considers that dreaming is exemplified by a sense of defocused attention, an abundance of unplanned, irrational associations and apparent loss of volitional control, features that may be associated with creative activity during wakefulness as well 
Since improvisation was also accompanied by changes in sensorimotor and limbic systems, it is tempting to speculate that these changes might be causally related, triggered in a top-down fashion by changes initiated in the prefrontal cortex. Increased activity in some of the sensory areas involved might be explained by their role in processing complex stimuli in the auditory modality. For example, the anterior temporal regions (anterior STG, MTG, and intervening STS) that were selectively activated during improvisation appear to play an integral role in processing complex features of highly structured acoustic stimuli, including music 
. However, we observed similar increases in other sensory areas as well. While some of these increases may simply reflect task-related processing in other modalities during improvisation, co-activation of multiple sensory areas also suggests the intriguing possibility that musical spontaneity is associated with a generalized intensification of activity in all sensory modalities. This possibility is supported by our findings of widespread activation of neocortical motor systems even though the analysis of MIDI data revealed no significant differences in number or distribution of piano notes played during improvised or control conditions. Therefore, rather than reflecting an increase in motor activity per se
, these activations may be associated with encoding and implementation of novel motor programs that characterize spontaneous improvisation.
Previous studies of music perception have reported both increases and decreases in limbic activity. Because of the presumed relationship between musical creativity and emotion, involvement of the limbic system was anticipated here. The deactivation of the amygdala and hippocampus we observed may be attributable to the positive emotional valence associated with improvisation, consistent with studies that have reported these limbic structures to be less active during perception of music that is consonant 
or elicits intense pleasure 
. However, we also observed more extensive deactivation of limbic structures in the hypothalamus, ventral striatum, temporal pole, and orbital cortex. The role played by these structures during improvisation will require further study.
In an intriguing neuroimaging study of musical improvisation in classically trained pianists, Bengtsson et al. 
found activations in the right dorsolateral prefrontal cortex, as well as premotor and auditory areas during improvisation. Our study differs from this one in several important ways. First, the study by Bengtsson et al. utilized contrasts that were designed to remove deactivations. In comparison, we had the explicit goal of identifying relevant deactivations that might support the notion of a hypofrontal state associated with creative activity. Hence, the masking strategies employed by our studies were fundamentally different, and would be expected to lead to divergent results. Second, our subjects were jazz pianists (rather than classical pianists). This difference is relevant in that jazz, much more so than classical music, is intrinsically characterized by improvisation. As a result, we believe that our findings reflect neural mechanisms behind improvisation in a perhaps more natural context, and certainly in musicians who have finely developed improvisational skills. Lastly, Bengtsson and coworkers utilized conditions in which musical improvisations were generated and then subsequently reproduced by memory. These conditions address an interesting facet of improvisation—the interaction between spontaneous musical performance and memory. We sought to eliminate the secondary impact of episodic memory encoding on improvisation by using either an over-learned or completely improvised condition (without a reproduction task in either condition).
Because our experiments were performed in highly trained musicians, it remains to be clarified whether or not our findings have characterized a higher qualitative level of musical output (as opposed to that which might be produced by less skilled performers). However, the similar findings seen for both Scale and Jazz paradigms, despite the musical simplicity of the former, strongly suggest that our findings are attributable to neural mechanisms that underlie spontaneity more broadly rather than those specific to high-level musicality alone. Taken together, the consistency of findings reported here suggests that the dissociation of activity in medial and lateral prefrontal cortices is attributable to the experimentally constant feature of improvisation and may be a defining characteristic of spontaneous musical creativity.