The Protective Action Encoding of Serotonin Transients in the Human Brain.

Area of Science:

• Neuroscience
• Neurochemistry
• Behavioral Economics

Background:

• The precise role of serotonin in human brain function is not well understood, partly due to challenges in measuring its local concentration in real-time.
• Existing theoretical models suggest a potential opposing relationship between serotonin and dopamine signaling.

Purpose of the Study:

• To measure local serotonin concentrations in the human striatum using fast-scan cyclic voltammetry.
• To investigate the correlation between serotonergic signaling and decision-making in a sequential investment game.
• To elucidate the functional role of serotonin in modulating behavior, particularly in response to negative feedback.

Main Methods:

• Fast-scan cyclic voltammetry was employed to infer serotonergic signaling.
• Measurements were taken from the striatum of 14 human patients diagnosed with Parkinson's disease.
• Participants engaged in a sequential investment game to observe decision-making processes.

Main Results:

• Serotonergic concentrations showed transient increases following negative reward prediction errors.
• Serotonin signaling reversed when counterfactual losses were predominant.
• Observed serotonin fluctuations correlated with decreased exposure to negative outcomes in subsequent trials.
• These findings provide initial evidence for serotonin acting antagonistically to dopamine signaling.

Conclusions:

• Serotonin signaling in the striatum appears to act as an opponent to dopamine, as predicted by theoretical models.
• Serotonin fluctuations are associated with inhibiting overreactions and promoting strategy persistence.
• The study suggests serotonin encodes a protective action strategy that mitigates risk and modulates choice selection, especially after adverse events.