Whether it is savoring an ice cream cone or learning that you got a good
deal on a recent purchase, two regions of your brain may move into gear.
Those regions, the nucleus accumbens and the orbitofrontal cortex, appear
to process the rewarding information that comes from engaging in such
The orbitofrontal cortex, which is known to process rewarding
information accruing from various types of activities, also processes
rewarding information stemming from social interactions. Along with the
nucleus accumbens, it appears to be one of the brain's major reward
Now it looks as if these two brain regions may also be involved in
processing the rewarding information that comes from engaging in social
interactions. The reason? People who are emotionally warm, sentimental, and
eager for people contact have been found to have significantly more gray
matter in these two brain areas than do people who are more self-contained and
The study was headed by psychiatrist Graham Murray, M.D., a Medical
Research Council clinician scientist at the University of Cambridge in
England, and his colleagues. Results were published online on May 20 in the
European Journal of Neuroscience.
As part of a large population study in Finland, some 2,000 young men were
assessed on temperament with the Cloninger Temperament and Character
Inventory, and out of these 2,000, 62 also underwent a structural MRI scan of
their brains. Satisfactory MRI scan results were obtained for 41 of the 62.
Murray and his team used the scan results for these 41 men, as well as the
temperament information about them, for their study. Specifically, they looked
to see whether there were any structural brain differences between subjects
who had scored high on "reward dependence," that is, on human
attachment, human dependence, openness to warm communication, and
sentimentality, and subjects who had scored low on this personality trait.
There were differences. Gray matter was significantly denser in the
orbitofrontal cortex and the nucleus accumbens in the subjects who had scored
high on reward dependence than in the subjects who had scored low on it.
These findings, the researchers noted, not only "provide strong
evidence for a brain structural disposition to social interaction," but
suggest that the same two areas of the brain that are critical for processing
reward information for some other types of activities are also critical for
processing reward information for social interactions.
Still another interesting finding emerged from the study. Gray matter on
the poles of the temporal lobes was significantly denser in the subjects who
had scored high on reward dependence than in the subjects who had not. So
these brain areas may also participate in the processing of reward information
that stems from social interactions.
As tantalizing as such findings are, they raise provocative questions. For
example, even though Murray and his colleagues found a link between a social
personality and the density of gray matter in specific regions of the brain,
can they really deduce from it that those particular brain areas process
Only indirectly, he admitted to Psychiatric News. "It could
be that social interaction itself drives brain growth in these regions rather
than the other way around. Personally I think it's likely to be a two-way
relationship; the more gray matter in these regions, the more pleasurable
social interaction is, and the more you interact, the more growth there is in
these regions. We'll need longitudinal studies of children or adolescents to
Since the same areas of the brain seem to be involved in processing various
types of rewards, could one type of reward perhaps be substituted for another
and thus satisfy people's need for rewards?
"It's a nice idea!" Murray replied. "But just because the
same brain circuits process information about different rewards, it doesn't
mean that your brain doesn't know the difference between sex and
Finally, what are the implications of these findings for psychiatrists?"
We studied individual differences in how much pleasure people take in
social interaction and related it to brain structure," Murray said."
But of course there are psychiatric disorders where the patients may
take little pleasure from social interaction—autism and schizophrenia,
for example. Could it be that variance in brain structure in these conditions
contributes to the lack of social pleasure experienced by the patients? I'm
keen to now look at this issue in patient studies. If brain structure is
important for this issue in patients, how can we address it? Biological
treatments could be one solution, but actually it's possible that long-term
social interventions may partly work by altering brain structure."
The study was funded by the Academy of Finland, Sigrid Juselius Foundation,
Stanley Medical Research Institute, Medical Research Council, and NARSAD.
An abstract of "The Brain Structural Disposition to Social
Interaction" is posted at<www3.interscience.wiley.com/journal/122394540/abstract>.▪