"The Human Brain Memorizes Event Frequencies While Forming Subjective Beliefs"
Mon, January 14, 2013 • 2:00 PM - 3:00 PM • SEA 4.244 (Library)
IRC/Psychology/Neurobiology Job Talk
In order to make adaptive choices, people need to estimate the probability of future events. It is generally assumed that probabilities are inferred by combining a priori, potentially subjective, knowledge with factual observations using Bayesian principles, but the precise neurobiological mechanism remains unknown. In my talk, I will explore whether neural encoding centers on subjective posterior probabilities, and data merely lead to updates of posteriors, or whether objective data are encoded separately alongside subjective knowledge. During fMRI, young adults acquired prior knowledge regarding uncertain events, repeatedly observed evidence in the form of stimuli, and estimated their probabilities. Participants combined the prior knowledge with the factual evidence along Bayesian principles. BOLD response in the default mode network (angular gyri, posterior cingulate, and medial prefrontal cortex) encoded the factual frequencies of stimuli, unaffected by prior knowledge. In this network, activity increased with frequencies and might reflect the accumulation of evidence in memory. In contrast, Bayesian posterior probabilities, computedfrom prior knowledge and stimulus frequencies, were encoded in bilateral inferior frontal gyrus. Here activity increased for improbable events and might reflect an attentional response to events which violate Bayesian predictions. My research thus uncovers a dual system of inference in the brain: empirical-based and knowledge-based. The advantage of separate encoding of empirical observations and subjective beliefs is that objective evidence can be recombined with newly acquired knowledge when a reinterpretation of the evidence is called for. This may provide a biological foundation for psychological therapies centered on re-visiting the past.