Sex and Gender Differences in Brain Structure and Function

Structural and Functional Differences Between Chromosomal Males and Females

Structural Differences

The Sexually Dimorphic Nucleus (SDN-POA)

Amygdala

Hippocampus

Corpus Callosum

Functional Differences

Default Mode Network

Research on sex differences in default mode network (DMN) activity has revealed several patterns, though it’s important to note that findings can vary across studies and individual differences are substantial.

Structural Differences

Connectivity Patterns: Females typically show stronger within-network connectivity in the DMN, particularly between key hubs like the posterior cingulate cortex, medial prefrontal cortex, and angular gyrus. Males often display more between-network connectivity, with stronger connections linking the DMN to other networks.

Network Topology: Females tend to have more bilateral DMN connectivity patterns, while males show more lateralized connectivity, particularly with stronger left-hemisphere dominance in some DMN regions.

Functional Differences

Resting-State Activity: Studies suggest females often exhibit higher baseline activity in DMN regions during rest, particularly in areas associated with self-referential thinking and social cognition, such as the medial prefrontal cortex and posterior cingulate cortex.

Task-Related Deactivation: Males may show more pronounced DMN deactivation during externally-focused cognitive tasks, while females sometimes maintain higher DMN activity even during task engagement.

Regional Variations

Medial Prefrontal Cortex: Females typically show greater activity and connectivity in ventromedial regions associated with emotional processing and self-reflection.

Posterior Cingulate/Precuneus: Sex differences in this region are less consistent, but some studies report higher female activity in areas linked to autobiographical memory and self-awareness.

Angular Gyrus: Females often show stronger connectivity in this region, which is involved in conceptual processing and theory of mind.

Functional Implications

These differences may relate to documented sex differences in:

• Self-referential processing: Females may engage more in introspective and self-focused thought
• Social cognition: Enhanced female DMN connectivity might support greater attention to social and emotional information
• Rumination patterns: Stronger DMN activity in females could relate to higher rates of rumination and mood disorders

Important Caveats

Individual Variation: There’s enormous overlap between males and females, with individual differences often exceeding group differences.

Methodological Considerations: Study findings can vary based on sample characteristics, scanning parameters, analysis methods, and whether participants are matched for factors like age and education.

Hormonal Influences: DMN activity can be influenced by hormonal fluctuations, particularly estrogen and progesterone cycles in females.

Development and Aging: Sex differences in DMN activity may change across the lifespan, with different patterns emerging during puberty, adulthood, and aging.

The research suggests meaningful sex differences in DMN function, but these should be understood as average tendencies rather than categorical differences, with significant implications for understanding conditions that affect DMN function differently across sexes, such as depression, anxiety, and autism spectrum disorders.

Language Processing

Spatial Processing