Sex Differences and Exogenous Estrogen Influence Learning and Brain Responses to Prediction Errors

Area of Science:

• Neuroscience
• Pharmacology
• Computational Psychiatry

Background:

• Mesocorticolimbic dopaminergic (DA) pathways are crucial for reward processing and implicated in addiction.
• Animal studies reveal significant sex differences and estrogen (E2) effects on these DA pathways.

Purpose of the Study:

• To investigate the combined effects of biological sex and estrogen levels on human reinforcement learning and the dopaminergic system.
• To explore how these factors modulate reward prediction error (RPE) signaling and learning rates.

Main Methods:

• A computational pharmacological fMRI study involving 67 males and 64 females in their low-hormone phase.
• Participants were randomly assigned to receive either E2 or placebo in a double-blind manner.
• Reinforcement learning task performance and associated brain activity were measured using fMRI.

Main Results:

• RPE-related brain activity was significantly enhanced in women compared to men.
• Elevated E2 levels further enhanced RPE-related activity in both sexes.
• Both female sex and E2 administration led to slower adaptation to RPEs, indicated by smaller learning rates.

Conclusions:

• Organizational sex differences and activational effects of E2 differentially impact DA release and receptor binding, explaining the observed discrepancy between enhanced RPE activity and reduced learning rates.
• Findings highlight the complex interplay of sex and estrogen in modulating the human dopaminergic system during reinforcement learning.