An Oxymoron? – Intelligent People Use Less of Their Brain.

No, wait, bigger is better, right? I mean, the larger the brain to body ratio, the smarter the species... Therefore bigger brains = more potential activations = higher intelligence.

Turns out it is more complicated than that. Bigger brains are indeed associated with higher intelligence (across, rather than within, species though), but intelligent people, in fact, may use less of their brains than their less intelligent counterparts! Rex E. Jung of the University of New Mexico and the Mind Research Network and Richard J. Haier of the UC Irvine were among the first to study intelligence using some of the most modern brain-imaging technology available to date. In one experiment, participants performed an intelligence test while their brain activity was recorded via PET technology. The surprising finding was that people who scored higher on the intelligence test had less brain activity, or, in other words, they used less brain energy while performing the test than their less intelligent counterparts!
In a follow-up study, Jung and Haier used PET scanning again to study people while they

played the game of Tetris for the first time, and then after a 50-day practice period. Not only brain activity in all participants decreased after practicing for 50 days, but more intelligent people showed the greatest brain activity decrease!From the first glance, these findings seem like an oxymoron - shouldn't smart people's brains make more connections, thus exhibiting more activity when thinking, especially on a difficult task such as an intelligence test? What Jung and Haier suggest, though, is that intelligent brains are just more efficient, making appropriate neural connections, and making them faster, thus providing more correct answers on an intelligence test.
What about Creativity and the Brain?
Although researchers disagree on the type of relationship between creativity and intelligence, most of them concur that such relationship exists. Jung and Haier, as well as several other researchers, report that similar to intelligent people, creative individuals show low levels of mental activity. Upon closer investigation, however, at least in one of such studies (Jausovec, 2000), the creativity task required participants to find solutions to creative problems. Such tasks seem similar to "convergent thinking" tasks, where usually only one correct, albeit creative, answer exists to any given problem. It appears then that such tests are akin to intelligence tests, thus, not surprisingly, the brain activity during such convergent thinking tasks is similar to brain activity during intelligence tasks. Perhaps this is also the reason convergent thinking is negatively associated with cranial dopamine levels (Akbari Chermahini & Hommel, 2010). Neurotransmitter dopamine has been linked to motivation and behavior activation. Hence the lower the dopamine levels, the lower the brain activity, the higher the convergent thinking.
I would suggest, however, that brain activity during divergent thinking would show a differentiated pattern. A person is required to come up with as many possible (creative) answers to a given problem while performing a divergent thinking test. It appears that in this case, the more is better, as more neural connections would lead to potentially more responses. In fact, several studies conducted by Colin Martindale and colleagues have shown that creative people have greater activity in some parts of the brain, and higher alpha activity during the inspiration stage of the creative process.
More studies will be needed to disentangle and confirm the above findings. At this time, however, we can say with a certain amount of confidence, that smarter brains require less energy to perform various tasks. We can also say that practice can lead to increased brain efficiency, again eventually requiring fewer resources. So keep practicing that guitar - with time you will literally need less brainpower to play like a pro!
References
Akbari Chermahini, S., & Hommel, B. (2010). The (b)link between creativity and dopamine: Spontaneous eye blink rates predict and dissociate divergent and convergent thinking. Cognition, 115, 458-465.
Jausovec, N. (2000). Differences in cognitive processes between gifted, intelligent, creative, and average individuals while solving complex problems: An EEG study. Intelligence, 28, 213-237.