Developmental sex differences in resting state functional connectivity of amygdala sub-regions

Abstract

During adolescence, considerable social and biological changes occur that interact with functional brain maturation, some of which are sex-specific. The amygdala is one brain area that has displayed sexual dimorphism, specifically in socio-affective (superficial amygdala [SFA]), stress (centromedial amygdala [CMA]), and learning and memory (basolateral amygdala [BLA]) processing. The amygdala has also been implicated in mood and anxiety disorders which display sex-specific features, most prominently observed during adolescence. Using functional magnetic resonance imaging (fMRI), the present study examined the interaction of age and sex on resting state functional connectivity (RSFC) of amygdala sub-regions, BLA and SFA, in a sample of healthy adolescents between the ages 10 and 16 years (n = 122, 71 boys). Whole-brain, voxel-wise partial correlation analyses were conducted to determine RSFC of bilateral BLA and SFA seed regions, created using the Eickhoff-Zilles maximum probability maps based on cytoarchitectonic mapping and FMRIB's Integrated Registration and Segmentation Tool (FIRST). Monte Carlo simulation was implemented to correct for multiple comparisons (threshold of 53 contiguous voxels with a z-value ≥ 2.25). Results indicated that with increasing age, there was a corresponding decrease in RSFC between both amygdala sub-regions and parieto-occipital cortices, with a concurrent increase in RSFC with medial prefrontal cortex (mPFC). Specifically, boys and girls demonstrated increased coupling of mPFC and left and right SFA with age, respectively; however, neither sex showed increased connectivity between mPFC and BLA, which could indicate relative immaturity of fronto-limbic networks that is similar across sex. A dissociation in connectivity between BLA- and SFA-parieto-occipital RSFC emerged, in which girls had weaker negative RSFC between SFA and parieto-occipital regions and boys had weaker negative RSFC of BLA and parieto-occipital regions with increased age, both standing in contrast to adult patterns of amygdala sub-regional RSFC. The present findings suggest relative immaturity of amygdala sub-regional RSFC with parieto-occipital cortices during adolescence, with unique patterns in both sexes that may support memory and socio-affective processing in boys and girls, respectively. Understanding the underlying normative functional architecture of brain networks associated with the amygdala during adolescence may better inform future research of the neural features associated with increased risk for internalizing psychopathology.

Keywords: Adolescence; Amygdala; Resting state functional connectivity; Sex differences.

Figure 1

Dorsal and lateral surface mapped results showing significant age-by-sex interactions (blue: negative, yellow: positive) in the coupling of amygdala sub-nuclei and other brain regions. Top left: Age-by-sex interaction with the left basolateral amygdala. Top right: Age-by-sex interaction with the right basolateral amygdala. Bottom left: Age-by-sex interaction with the left superficial amygdala. Bottom right: age-by-sex interaction with the left basolateral amygdala. All findings underwent Monte Carlo multiple comparisons correction (z ≥ 2.25).

Figure 2

Fisher's Z transformed R-values from brain regions with significant functional connectivity age-by-sex interactions with left basolateral amygdala (left) and right basolateral amygdala (right) were extracted and plotted against age and by sex.

Figure 3

Fisher's Z transformed R-values from brain regions with significant functional connectivity age-by-sex interactions with left superficial amygdala (left) and right superficial amygdala (right) were extracted and plotted against age and by sex.