2013年10月28日月曜日

Hierarchical Prediction Errors in Midbrain and Basal Forebrain during Sensory Learning

Sandra Iglesias, Christoph Mathys, Kay H. Brodersen, Lars Kasper, Marco Piccirelli, Hanneke E.M. den Ouden, Klaas E. Stephan
Neuron, Volume 80, Issue 2, 519-530, 16 October 2013

ヒトfMRI。
「手掛かり刺激と結果の連合強度」や「その強度の不安定さ(ボラティリティ)」など、「環境についての様々なレベルの情報」についての学習がヒトの脳内でどのように行われているのか?
低次な予測誤差(刺激と結果の連合の学習に利用される)は中脳(midbrain、ドーパミン系)で処理され、高次な予測誤差(連合の不安定さの学習に使われる)は前脳基底部(basal forebrain、アセチルコリン系)で処理されている。

In Bayesian brain theories, hierarchically related prediction errors (PEs) play a central role for predicting sensory inputs and inferring their underlying causes, e.g., the probabilistic structure of the environment and its volatility. Notably, PEs at different hierarchical levels may be encoded by different neuromodulatory transmitters. Here, we tested this possibility in computational fMRI studies of audio-visual learning. Using a hierarchical Bayesian model, we found that low-level PEs about visual stimulus outcome were reflected by widespread activity in visual and supramodal areas but also in the midbrain. In contrast, high-level PEs about stimulus probabilities were encoded by the basal forebrain. These findings were replicated in two groups of healthy volunteers. While our fMRI measures do not reveal the exact neuron types activated in midbrain and basal forebrain, they suggest a dichotomy between neuromodulatory systems, linking dopamine to low-level PEs about stimulus outcome and acetylcholine to more abstract PEs about stimulus probabilities.

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