\input zb-basic \input zb-ioport \iteman{io-port 05298177} \itemau{Samejima, Kazuyuki; Doya, Kenji} \itemti{Estimating internal variables of a decision maker's brain: A model-based approach for neuroscience.} \itemso{Ishikawa, Masumi (ed.) et al., Neural information processing. 14th international conference, ICONIP 2007, Kitakyushu, Japan, November 13--16, 2007. Revised selected papers, Part I. Berlin: Springer (ISBN 978-3-540-69154-9/pbk). Lecture Notes in Computer Science 4984, 596-603 (2008).} \itemab Summary: A major problem in search of neural substrates of learning and decision making is that the process is highly stochastic and subject dependent, making simple stimulus- or output-triggered averaging inadequate. This paper presents a novel approach of characterizing neural recording or brain imaging data in reference to the internal variables of learning models (such as connection weights and parameters of learning) estimated from the history of external variables by Bayesian inference framework. We specifically focus on reinforcement leaning (RL) models of decision making and derive an estimation method for the variables by particle filtering, a recent method of dynamic Bayesian inference. We present the results of its application to decision making experiment in monkeys and humans. The framework is applicable to wide range of behavioral data analysis and diagnosis. \itemrv{~} \itemcc{} \itemut{} \itemli{doi:10.1007/978-3-540-69158-7\_62} \end