We humans are a creative species. When we compare what we do and make with what other species do and make, it is self-evident that we are the most creative species. But what has the role of creativity been over the course of our evolution? Is it just a by-product, an emergent property, of more fundamental cognitive processes, such as those involving problem-solving ability, memory, language, attention, and so on? Or is creativity a distinct and identifiable cognitive process of its own, which varies from individual-to-individual? Heritable genetic variation is the raw material on which natural selection works, so assessing the plausibility of creativity as an important human adaptation depends on understanding variation at both the genetic and neuroanatomical levels.
Psychologists have studied creativity for decades, developing a variety of tests to assess creativity and creative potential in individuals. Using these tests to guide them, cognitive neuroscientists are now using sophisticated neuroimaging tools to assess the neuroanatomical differences between more-creative and less-creative individuals, with the hopes of developing an understanding of creativity from the bottom-up, so to speak. If we are ever to understand creativity in an evolutionary perspective, then we must be able to link the extraordinary painting or inspired insight to the brain structures from which they sprang. This may sound unduly reductionist and coldly scientific to some (you know who you are), but understanding creativity should not make us appreciate it any less. I think it's safe to say that scientists who devote their time and energy to studying creativity probably have as deep an appreciation for the creative process and its results as anyone.
In the 1970s, based on studies of split-brain patients, the idea that the right hemisphere "controlled" creativity became very popular, especially in the public's imagination. This model is now considered overly simplistic; Alice Flaherty (2005, Journal of Comparative Neurology 493:147-153) has provided us with an updated model for the neurological control of creativity, based on research from neuroimaging, lesion analysis, and the effects of drugs. She begins with a definition (p. 147): "A creative idea will be defined simply as one that is both novel and useful (or influential) in a particular social setting." She is concerned that any neurological model of creativity should focus not just on artistic outlets (such as painting and music) but encompass other domains, such as language and mathematics. Such a model is necessarily going to have to involve a network of brain regions, rather than be localized to one part of the brain or one hemisphere. Flaherty proposes first that cortical interactions between the temporal and frontal lobes are critical for regulating creative expression. Temporal lobe deficits can increase the generation of creative ideas, sometimes at the expense of quality, as in various manic states. In contrast, frontal lobe deficits can inhibit creative thinking. Thus via mutually inhibitory pathways, the frontal and temporal lobes work together to not simply generate ideas but those that are "novel and useful"--creative ideas.
In addition to the fronto-temporal network, another brain system is also critical for creative expression: the dopamine pathways of the subcortical limbic system (which also have strong connections to parts of the frontal lobe). Being creative is not a passive process, and creative people are more responsive to sensory stimulation, have higher baseline levels of arousal, and increased goal-directed behavior. In Flaherty's model, people vary in terms of their level of creative drive according to the activity of the dopamine pathways of the limbic system. Dopamine mediates reward-seeking behavior and appreciation for music and beautiful faces--Flaherty suggests that creative motivation also originates in these dopaminergic pathways. The evidence for the involvement in dopamine in creativity comes primarily from drug studies: dopamine agonists (such as cocaine and levodopa) heighten arousal and goal-seeking behaviors while dopamine antagonists (such as antipsychotics) can shut down the free associations that may be necessary for creativity.
Flaherty's model is presented quite clearly and succinctly, and I recommend her paper to anyone as a starting point in exploring the brain and creativity. A couple of papers have been published recently that are clearly relevant to the model. First, Rex Jung and his colleagues (2010, Human Brain Mapping 31:398-409) looked at the correlation between creativity and regional cortical thickness in a group of 61 young adult men and women. They assessed creativity using an instrument called the Creative Achievement Questionnaire, which assesses creativity in ten different domains (e.g., visual arts, music, etc.); in addition, divergent thinking was tested using a variety of design tasks, with the results consensually assessed by raters into a "composite creativity index." Magnetic resonance images of the subjects' brains were compared to one another, and an automated program was used to look at the correlation between the various creative measures and the cortical thickness (the surface gray matter) of the subjects' brains.
Jung and colleagues found several brain regions in which cortical thickness showed statistically significant correlations with performance on these tests of creativity and divergent thinking. These regions were in both hemispheres and included parts of the frontal lobe, and regions on the border between the temporal and occipital/parietal lobes. Without worrying too much about the specific regions here, these results strongly suggest that creativity in the brain does not depend on a specific region or hemisphere but on a dispersed network of brain regions. This is consistent with Flaherty's model, although the regions involved were not all predicted by that model. Furthermore, not all of the statistical associations identified by Jung and colleagues were positive. Composite creative index (CCI) scores were positively correlated with increased thickness in the right posterior cingulate cortex (this is the cortex that surrounds the corpus callosum on the medial surface of the hemisphere, near the medial portion of the frontal lobe); however, CCI scores were negatively correlated with cortical thickness in the left lingual gyrus (another medial surface structure located close to the boundary between the occipital and temporal lobes). Obviously, these results do not support a simple more-is-better model; however, they are consistent with aspects of the Flaherty model, which posits that creativity results in part from mutually inhibitory interactions between parts of the frontal and temporal lobes.
Another paper using a similar methodology sheds some light on the association between the size of dopamine-rich regions of the brain and creativity. In this study by Hikaru Takeuchi and colleagues (2010, NeuroImage 51:575-585), regional brain volume (assessed from MRIs using an automated program) was correlated with performance on a test of creativity and divergent thinking (the S-A creativity test). They found strong associations between performance on this test and larger gray matter volume in dopamine-rich subcortical regions such as the substantia nigra and other fronto-striatal regions; in addition, a portion of the right dorsolateral prefrontal cortex was also correlated with higher creative test performance. Takeuchi and colleagues see their results as supporting the important role of dopamine in creative thinking, but they also stress that this is in the context of a more expansive brain network.
From an evolutionary perspective, these studies provide a couple of potential insights. First, there is clearly quantitative individual variation in creativity that is associated with neuroanatomical variation. Of course, we do not know if this is due to genetics or the environment, but it gets us a step closer to understanding the material basis of creativity, which is an important first step. Second, both studies show that performance on these tests of creativity were largely independent of performance on basic intelligence tests (with the caveat that the subjects were mostly college students with above average in intelligence). Both intelligence (in the IQ test sense) and creativity appear to be the products of widely distributed functional networks in the brain, which are at least partly independent of one another. This leaves open the possibility that creativity, in evolutionary terms, is not simply an emergent property of increased intelligence.