Serotonin encodes surprise

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While the dopamine system encodes reward/punishment information (Schultz2016), serotonin appears to encode non-specific surprise (Matias2017).

• Optogenetics in mice have revealed 5-HT-expressing neurons in the dorsal raphe nuclei fire in response to unexpected outcomes independent of their value sign (valence)

Averaged surprise is fundamentally equivalent to uncertainty, and therefore synonymous with entropy (Bestmann2008)

It is possible that serotonin relaxes prior assumptions so as to weaken perseverative/habitual responding (Carhart-Harris2017a, Matias2017) to facilitate new learning, in conditions where prior assumptions become counterproductive. This would be consistent with predictive processing, and the REBUS model.

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Related Notes

Ref: Carhart-Harris2018