Cortical Connections Position Primate Area 25 as a Keystone for Interoception, Emotion, and Memory

Area of Science:

• Neuroscience
• Affective Neuroscience
• Primate Neuroanatomy

Background:

• Subgenual cingulate area 25 (A25) integrity is critical for emotional processing and homeostasis.
• Disruptions in A25 are linked to mood disorders, but its full cortical connectivity remains uncharacterized.
• A25 plays a key role in affective networks, influencing emotional expression and equilibrium.

Purpose of the Study:

• To systematically map the cortical connections of subgenual area 25 (A25) in rhesus monkeys.
• To elucidate the neural circuitry underlying A25's role in emotion, cognition, and homeostasis.
• To provide a circuit basis for understanding A25's vulnerability in psychiatric and neurologic disorders.

Main Methods:

• Utilized neural tracers in rhesus monkeys to investigate A25's structural and functional connectivity.
• Analyzed termination patterns within cortical layers to infer functional effects (excitatory/inhibitory).
• Correlated anatomical findings with known functions of connected brain regions.

Main Results:

• Identified dense connections between A25 and ventromedial/posterior orbitofrontal areas involved in emotion and homeostasis.
• Revealed a moderate pathway from A25 to frontopolar area 10, potentially regulating negative affect.
• Found connections with auditory, memory-related medial temporal, and interoceptive anterior insula cortices, with specific laminar targeting suggesting dominant excitatory effects in PFC and inhibitory gating in entorhinal cortex.

Conclusions:

• A25 functions as a central feedback system within the prefrontal cortex, integrating emotional, cognitive, and homeostatic information.
• Specific pathways, particularly to area 10, offer potential therapeutic targets for mood disorders by modulating negative affect.
• The detailed connectivity and laminar patterns provide a circuit-level understanding of A25's role in psychiatric and neurological conditions.