Subjects with a low reactive temperament at 4 months had a thicker cortex in a region of left orbitofrontal cortex compared with those with a high reactive temperament, whereas high reactives had thicker cortex than low reactives in a region of right ventromedial prefrontal cortex (See and ). There was no difference in cortical thickness between the genders, nor any interaction between temperament and gender in either of these regions.
Right Ventromedial Prefrontal Cortical Thickness Difference Map
illustrates the 225 mm2 region of left OFC that was thicker in the 18 year olds who had a low reactive temperament, compared with those who were high reactive infants. The point of maximal thickness difference between the two temperamental groups, marked with a bright blue spot, lies in the transverse orbital sulcus. The cluster extends into the anterior-lateral portion of the posterior orbital gyrus, the most extreme lateral aspect of the medial orbital gyrus, the most extreme medial aspect of the lateral orbital gyrus and pars orbitalis, and the most posterior aspect of the anterior orbital gyrus. This cluster bridges several anatomical regions as defined by surface gyral and sulcal anatomy. illustrates the 169 mm2 region of right ventromedial prefrontal cortex (VmPfc) that was thicker in the 18 year olds who had a high reactive temperament in infancy, compared with those subjects who were low reactive infants. This cluster is located on the medial wall of the gyrus rectus of the VmPfc. The cluster extends diagonally across the medial wall of the rectus gyrus angled upwards from its most inferior/posterior territory to the most superior aspect of the cluster which is more anterior. The most superior aspect extends to include cortex lying within the superior rostral sulcus, which defines the most superior extent of the rectus gyrus on the medial wall.
shows the range of Talairach coordinates that occur in the regions illustrated in and , and the Talairach coordinates of the vertex at which the thickness difference between the temperament groups is greatest.
Range and Maxima of Talairach Coordinates of regional cortical thickness differences between temperaments
The two major contemporary maps of the human OFC are by Petrides and colleagues50, 51
, and by Price and Ongur52, 53
. In the Petrides’ map, the location of the left orbitofrontal cluster would correspond primarily to area 13, bounded by a transitional zone between 13 and 47/12 laterally, areas 13 and 11 anteriorally, and the junction of 13 and 14 medially. In the more fine-grained schema of Price and Ongur, the cluster would correspond to cortex in areas 47/12m, 13l, and 11l and is bounded by the transitions between 47/12m and 47/12l laterally, 47/12m and 11l anteriorally, and the junction of 13m and 13l medially.
The right ventromedial cluster, which is thicker in the high reactives, lies on the medial wall of the cerebral hemisphere and would correspond in the Petrides map to limbic cortex within areas 14 in the inferior/posterior part of the cluster and area 32 in the superior/anterior part of the cluster. In Price and Ongur’s map, the most posterior aspect of the cluster would correspond to area 14r; the cluster extends into the most posterior aspect of area 11m and the most inferior/anterior corner of area 10m, before reaching area 10r at the its most superior and anterior aspect.
Vertex-wise analyses did not reveal any additional clusters of thickness differences between the two temperament groups that survived correction for multiple comparisons at the whole brain level. In addition to this whole brain approach, as we had predicted, the posterior comparison region of visual cortex (cuneus, pericalcarine, and lingual gyrus) did not show significant difference in cortical thickness between groups [Left: Low Reactive (LR) (Mean ± SEM) 1.81 ± .015 vs. High Reactive (HR) 1.81± .017, t(74) = 0.05, p= .96; Right: LR 1.87 ± .017 vs. HR 1.86± .016, t(74) = 0.37, p= .71].
Because the cluster method detects thickness differences at adjacent vertices, we wondered if there was any evidence of additional scattered thickness differences related to temperament in ventral prefrontal cortex. Analysis of the residual territory in ventral prefrontal cortex that remained after clipping out the territories of the clusters in & showed no evidence of such diffuse thickness differences between the groups [Left: Low Reactive (LR) (Mean ± SEM) 2.58 ± .020 vs. High Reactive (HR) 2.56± .021, t(74) = 0.83, p= .41; Right: LR 2.51 ± .023 vs. HR 2.50± .024, t(74) = 0.45, p= .66].
Because social anxiety disorder in adolescence has been linked to an inhibited temperament, we asked whether our results might be due to a confounding with the use of medication, social anxiety disorder, or major depressive disorder. The results indicated that the thickness differences between the temperament groups were not associated with any of these factors ().
Mean +/−SEM cortical thickness by temperament in subjects without Social anxiety disorder, MDD and history of medication use