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Babayan, Benedicte

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Babayan

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Benedicte

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Babayan, Benedicte

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Author's Publications: search.filters.isAuthorOfPublication.5d5b9832-96a1-4baa-af01-eef6923bda9e

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    Dopamine reward prediction errors reflect hidden state inference across time
    (2017) Starkweather, Clara; Babayan, Benedicte; Uchida, Naoshige; Gershman, Samuel
    Midbrain dopamine neurons signal reward prediction error (RPE), or actual minus expected reward. The temporal difference (TD) learning model has been a cornerstone in understanding how dopamine RPEs could drive associative learning. Classically, TD learning imparts value to features that serially track elapsed time relative to observable stimuli. In the real world, however, sensory stimuli provide ambiguous information about the hidden state of the environment, leading to the proposal that TD learning might instead compute a value signal based on an inferred distribution of hidden states (a ‘belief state’). In this work, we asked whether dopaminergic signaling supports a TD learning framework that operates over hidden states. We found that dopamine signaling exhibited a striking difference between two tasks that differed only with respect to whether reward was delivered deterministically. Our results favor an associative learning rule that combines cached values with hidden state inference.
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    Opposite initialization to novel cues in dopamine signaling in ventral and posterior striatum in mice
    (eLife Sciences Publications, Ltd, 2017) Menegas, William; Babayan, Benedicte; Uchida, Naoshige; Watabe-Uchida, Mitsuko
    Dopamine neurons are thought to encode novelty in addition to reward prediction error (the discrepancy between actual and predicted values). In this study, we compared dopamine activity across the striatum using fiber fluorometry in mice. During classical conditioning, we observed opposite dynamics in dopamine axon signals in the ventral striatum (‘VS dopamine’) and the posterior tail of the striatum (‘TS dopamine’). TS dopamine showed strong excitation to novel cues, whereas VS dopamine showed no responses to novel cues until they had been paired with a reward. TS dopamine cue responses decreased over time, depending on what the cue predicted. Additionally, TS dopamine showed excitation to several types of stimuli including rewarding, aversive, and neutral stimuli whereas VS dopamine showed excitation only to reward or reward-predicting cues. Together, these results demonstrate that dopamine novelty signals are localized in TS along with general salience signals, while VS dopamine reliably encodes reward prediction error. DOI: http://dx.doi.org/10.7554/eLife.21886.001