Journal of Behavioral and Brain Science, 2013, 3, 49-56 http://dx.doi.org/10.4236/jbbs.2013.31005 Published Online February 2013 (http://www.scirp.org/journal/jbbs) What Are the Chances? fMRI Correlates of Observing High and Low-Probability Actions Roger Newman-Norlund 1 , Kim Bruggink 2 , Raymond Cuijpers 3 , Harold Bekkering 2 1 Department of Exercise Science, University of South Carolina, Columbia, USA 2 Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen, Nijmegen, The Netherlands 3 Industrial Engineering & Innovation Sciences, Human Technology Interaction Group, Eindhoven University of Technology, Eindhoven, The Netherlands Email: rnorlund@mailbox.sc.edu Received October 5, 2012; revised November 7, 2012; accepted November 15, 2012 ABSTRACT Cognitive scientists often use probabilistic equations to model human behavior in ambiguous situations. How, where, and even if such probabilities are represented in the human brain remains largely unknown. Here, we manipulated the probability of simple bottle-pouring action based on two considerations, the relative fullness of two glasses and the rela- tive distance between the two glasses and the bottle. Whole brain functional magnetic resonance imaging was used to measure brain activity while participants viewed probable and improbable pouring actions. Improbable actions elicited increased activity in the theory of mind (ToM) network, commonly found active when trying to grasp the intentions of others, whereas probable actions elicited increased activity in the human mirror neuron system (hMNS) and areas asso- ciated with mental imagery and memory. These data provide novel insight into the brain mechanisms humans use to distinguish between high and low-probability actions. Keywords: Probability; fMRI; Human Mirror Neuron System; Action Observation 1. Introduction The ability to make predictions about the future state of the world when placed in ambiguous situations is a fun- damental and very useful capacity present in humans. Athletes predict the actions of their opponents, mothers make predictions regarding their baby’s needs, and wri- ters predict the responses of their reviewers. Cognitive scientists have long relied on probabilistic models to ex- plain a wide variety of complex human behaviors in- cluding decision making, action planning, motor learning and behavior [1-5]. Probabilistic models are especially apt at making predictions in ambiguous situations like those mentioned above. In such models, events are typi- cally assigned a specific likelihood after taking into ac- count the current situation and prior experience accord- ing to a well known statistical approach known as em- pirical Bayes. While significant research has been con- ducted with regards to the neural correlates of probabili- ties as they relate to topics such as reinforcement learn- ing, risk taking behavior and reward [6-9], relatively lit- tle is known about the neural representation of action probabilities as they relate to object-directed actions en- countered in everyday situations. In the current experi- ment, we attempted to localize brain areas responsible for coding the probability of actions. Specifically, we con- ducted a functional magnetic resonance imaging (fMRI) experiment in which we could visualize brain activity during the observation of actions that were either likely or unlikely based on the relative distance between objects being combined or the context in which the combination of objects occurred. Based on previous research, we had strong reason to believe that human mirror neuron system (MNS) would be involved in the calculation of action probabilities. The MNS, a system comprised of the human inferior parietal and frontal lobes, is often cited as supporting various as- pects of action understanding. Activity within this system is modulated by the type of action sequences that are “likely” to follow a particular observed movement [10- 13]. For example, Fogassi and colleagues [14] found that activity recorded from primate MNs during the grasp of a peanut depends critically on whether the peanut was then eaten or placed in a cup. In humans, Iacoboni and col- leagues [15] showed that activity recorded from the human MNS during the observation of a grasping action also varies as a function of the subsequent to-be per- formed movements. This sensitivity to future actions, highly relevant to the discussion of action probabilities, has been referred to as “action forecasting”. Here, the idea is that MNs respond most strongly to actions which Copyright © 2013 SciRes. JBBS