Results from a recent study from researchers at the University of Utah indicate that there is no evidence to support the theory that some people are "right-brained," while others are "left-brained," giving you one less easy way to dismiss someone's peculiar personality.
There has never been strong evidence to uphold this distinction, but the theory stemmed from the notion that there were two distinct personality types, based on which hemisphere of the brain was dominant. The more active side would have noticeable effects on personality and cognition. "Right-brained" people are supposedly more creative with strong concentration powers. People who are "left-brained" are more analytical, logical, and better with language.
Researchers for the study monitored the fMRI brain scans of 1011 participants, all between the ages of 7 to 29, and did not detect support of brain hemisphere dominance. The participants were asked to think about nothing for five to ten minutes (resting brain state/pre-nap state). The researchers then looked at "each pair of 7266 regions covering the gray matter" (complicated brain stuff, but this sounds like a lot of the brain). According to the study's lead author, Jared Nielsen:
"We just don't see patterns where the whole left-brain network is more connected or the whole right-brain network is more connected in some people. It may be that personality types have nothing to do with one hemisphere being more active, stronger, or more connected..."
Certainly, some people are more creative, some people are more analytical, but this doesn't reflect in brain dominance. Nielsen encourages people to be more specific with their descriptions rather than just spouting sides to talk about people:
"Everyone should understand the personality types associated with the terminology 'left-brained' and 'right-brained' and how they relate to him or her personally."