Friday, January 11, 2008

East Asian & American brain activity - what does fMRI say?   posted by Razib @ 1/11/2008 05:20:00 PM

Culture Influences Brain Function, Study Shows:

To find out, a team led by John Gabrieli, a professor at the McGovern Institute for Brain Research at MIT, asked 10 East Asians recently arrived in the United States and 10 Americans to make quick perceptual judgments while in a functional magnetic resonance imaging (fMRI) scanner--a technology that maps blood flow changes in the brain that correspond to mental operations.

Subjects were shown a sequence of stimuli consisting of lines within squares and were asked to compare each stimulus with the previous one. In some trials, they judged whether the lines were the same length regardless of the surrounding squares (an absolute judgment of individual objects independent of context). In other trials, they decided whether the lines were in the same proportion to the squares, regardless of absolute size (a relative judgment of interdependent objects).

In previous behavioral studies of similar tasks, Americans were more accurate on absolute judgments, and East Asians on relative judgments. In the current study, the tasks were easy enough that there were no differences in performance between the two groups.

However, the two groups showed different patterns of brain activation when performing these tasks. Americans, when making relative judgments that are typically harder for them, activated brain regions involved in attention-demanding mental tasks. They showed much less activation of these regions when making the more culturally familiar absolute judgments. East Asians showed the opposite tendency, engaging the brain's attention system more for absolute judgments than for relative judgments.

As noted in the summary there have been previous behavioral/psychological studies which pointed to this difference, the book Geography of Thought surveyed that literature. I can't find the paper online yet, or on the site of Psychological Science, so the question I have is what was the ethnic make up of the "10 Americans"? In the previous psychological work it seems that Asian Americans tend to cluster with other Americans if they arrived as small children, but more with Asians if they arrived as adults (with teenagers somewhere in between). That argues for some level of plasticity in regards to this sort of cognition, or at least a critical period. If the fMRI confirmed this, that is, Asian Americans born in the United States exhibit signatures similar to European Americans, then that would suggest that this sort of cognitive function is subject primarily to cultural variation.

You might think "of course it is a function of culture," but do note that the physical differences in shape across brains. And recent signatures of selection show that East Asians have derived alleles on genes which are involved in development of the structure of the brain. Finally, East Asian and European infants seem to have very different initial personalities. So I don't think the priors here are clean cut at all. Culture influences the shape of our genome and biology; LCT anyone?

Note: If there is a difference between East Asians and Europeans even before or controlling for acculturation on these sorts of tasks, I would suspect that it would be a small average difference when considered in light of the difference phenotypes. I suspect that small differences in means can lead to different metastable cultural norms. Or, more clearly, small differences in propensity of East Asian origin people raised in Western culture to think in a particular manner may totally be dampened by the other exogenous inputs (primarily, the constant interaction with people of European origin with cultural norms at sharp variance with those dominant in East Asia). But as the frequency of East Asians increases one could imagine that a likelihood might exist that a "peak shift" might occur so that East Asian Americans in predominantly East Asian neighborhoods and socialized by those of the same ethnicity may develop a subculture more at variance with the European American norm and similar to what we see in East Asia. In other words, non-linearities due to gene-environment correlation & interaction.