Significant phenotypic correlations between surface area and cigarette pack-years (-0.13 < rP < -0.11, p = 0.0001-0.02) explained by significant unique environmental factors (-0.13< covE < -0.10, p = 0.005-0.04) were observed for three specific regions within the frontal lobe and cingulate cortex. These regions include the right rostral middle frontal, left posterior cingulate, and left pars orbitalis (Table II). The magnitude of the environmental covariance was fairly consistent across adjusted and unadjusted measures of surface area, although the relationship between the left pars orbitalis was no longer significant after adjustment for surface area (Table III). The average environmental covariance among unadjusted ROIs was -0.12 while those adjusted for total surface area was -0.13.
