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Probabilistic reasoning by neurons

Abstract

Our brains allow us to reason about alternatives and to make choices that are likely to pay off. Often there is no one correct answer, but instead one that is favoured simply because it is more likely to lead to reward. A variety of probabilistic classification tasks probe the covert strategies that humans use to decide among alternatives based on evidence that bears only probabilistically on outcome. Here we show that rhesus monkeys can also achieve such reasoning. We have trained two monkeys to choose between a pair of coloured targets after viewing four shapes, shown sequentially, that governed the probability that one of the targets would furnish reward. Monkeys learned to combine probabilistic information from the shape combinations. Moreover, neurons in the parietal cortex reveal the addition and subtraction of probabilistic quantities that underlie decision-making on this task.

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Figure 1: Probabilistic categorization task.
Figure 2: Responses of an LIP neuron during probabilistic classification.
Figure 3: Population analyses.
Figure 4: Effect of individual shapes on LIP activity.
Figure 5: The effect of logLR on firing rate is not explained by motor planning.

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Acknowledgements

We thank H. Brew, A. Churchland, T. Hanks, R. Kiani and J. Palmer for advice and comments, M. Mihali and V. Skypeck for technical assistance, and M. McKinley for preparing movie demonstrations. This work was supported by the Howard Hughes Medical Institute (HHMI) and grants from the NEI and NCRR.

Author Contributions The authors designed the project together. T.Y. collected data and performed the data analysis. T.Y. and M.N.S. wrote the paper.

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Correspondence to Tianming Yang or Michael N. Shadlen.

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Supplementary information

Supplementary Information

This file contains Supplementary Notes divided into the following parts: A. Conditional dependency and alternatives to the logLR; B. A simple illustration of conditional dependence; C. Effect of target configuration on the representation of logLR; D. Guide to Supplementary Movies and finally Supplementary Figures 1-8 and Legends (PDF 3484 kb)

Supplementary Movie 1

This file contains Supplementary Movie 1 which is an example of a trial from the experiment; corresponding to Movie 1 in Appendix D. (MOV 175 kb)

Supplementary Movie 2

This file contains Supplementary Movie 2 which is an example of a trial from the experiment; corresponding to Movie 2 in Appendix D. (MOV 774 kb)

Supplementary Movie 3

This file contains Supplementary Movie 3 which is an example of a trial from the experiment; corresponding to Movie 3 in Appendix D. (MOV 110 kb)

Supplementary Movie 4

This file contains Supplementary Movie 4 which is an example of a trial from the experiment; corresponding to Movie 4 in Appendix D. (MOV 92 kb)

Supplementary Movie 5

This file contains Supplementary Movie 5 which is an example of a trial from the experiment; corresponding to Movie 5 in Appendix D. (MOV 226 kb)

Supplementary Movie 6

This file contains Supplementary Movie 6 which is an example of a trial from the experiment; corresponding to Movie 6 in Appendix D. (MOV 105 kb)

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Yang, T., Shadlen, M. Probabilistic reasoning by neurons. Nature 447, 1075–1080 (2007). https://doi.org/10.1038/nature05852

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