Activity in inferior parietal and medial prefrontal cortex signals the accumulation of evidence in a probability learning task

PLoS Comput Biol. 2013;9(1):e1002895. doi: 10.1371/journal.pcbi.1002895. Epub 2013 Jan 31.


In an uncertain environment, probabilities are key to predicting future events and making adaptive choices. However, little is known about how humans learn such probabilities and where and how they are encoded in the brain, especially when they concern more than two outcomes. During functional magnetic resonance imaging (fMRI), young adults learned the probabilities of uncertain stimuli through repetitive sampling. Stimuli represented payoffs and participants had to predict their occurrence to maximize their earnings. Choices indicated loss and risk aversion but unbiased estimation of probabilities. BOLD response in medial prefrontal cortex and angular gyri increased linearly with the probability of the currently observed stimulus, untainted by its value. Connectivity analyses during rest and task revealed that these regions belonged to the default mode network. The activation of past outcomes in memory is evoked as a possible mechanism to explain the engagement of the default mode network in probability learning. A BOLD response relating to value was detected only at decision time, mainly in striatum. It is concluded that activity in inferior parietal and medial prefrontal cortex reflects the amount of evidence accumulated in favor of competing and uncertain outcomes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Frontal Lobe / physiology*
  • Humans
  • Learning
  • Magnetic Resonance Imaging
  • Parietal Lobe / physiology*
  • Probability*

Grant support

The study was supported by the AXA Insurance Research Fund, Centre d'Imagerie BioMédicale of the University of Lausanne, Centre Hospitalier Universitaire Vaudois, Ecole Polytechnique Fédérale de Lausanne, University of Geneva, Hopitaux Universitaires de Genève, the Leenaards and Jeantet Foundations, and the Swiss Finance Institute. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.