Schoenemann, P. Thomas, 1999, "Relationships between prefrontal volume and behavior in normal human females," (abstract of paper presented) American Journal of Physical Anthropology,  Supplement 28:244.

Not only did the hominid brain increase more than three-fold in size during our evolutionary history, but it appears that certain areas of the brain contributed more to this increase than others.  In particular, the prefrontal region appears to be twice as large (considered as a percentage of cortical surface area) as homologous regions in non-human primates.

It is not clear why this region of the brain shows such a disproportionate increase.  The prefrontal region is not involved in primary sensory processing, but rather appears to be important for higher-order cognitive tasks, such as planning and strategy.  Areas in the prefrontal cortex also appear to be important for breaking perseverative tendencies, and for memory of serial order.  However, whether variability in prefrontal volume and/or surface areas may be correlated with specific behavioral abilities has not been extensively investigated in normal humans.

The present study assessed the extent to which prefrontal volumes and surface-areas correlate with a variety of psychometric tests, both between- and within-families.  36 pairs of sisters (72 individuals total) where given a diverse battery of cognitive tests that included four tests known clinically to show prefrontal specificity: STROOP, TRAILS, WCST, and VERBAL FLUENCY.  High-resolution MRI brain scans (voxel size: ~1.3 mm3, with no gaps between slices) where obtained, from which prefrontal volumes and surface where quantified.  Within- and between-family correlations were calculated (controlling for age and simple reaction time) among the behavioral and neuroanatomical variables.

The results showed that between-families two tests correlated significantly with prefrontal volumes: STROOP and TRAILS.  Within-families, the STROOP test (but not TRAILS) remained significant. These findings suggest that significant correlations may exist between localized neuroanatomical volumes and specific cognitive abilities.  Details of the STROOP and TRAILS tests are given, and possible evolutionary implications of these findings are discussed.