Foraging and choosing between multiple options

Matthew Rushworth
Department of Experimental Psychology, University of Oxford

Many investigations of the neural mechanisms have focused on binary decisions – choosing between two 
options. In a recent investigation we used a biophysical model of decision-making to explore how choices 
representations might change when decisions when there are three potential options. The model 
predicted that it would be more difficult to choose accurately between two options with similar values in 
the presence of a third alternative with a low value rather than a high value. Human subject choices 
conformed to this prediction as did fMRI-recorded value difference signals in the ventromedial 
prefrontal cortex (vmPFC). Individual differences in the modulation of vmPFC signals predicted individual 
differences in the degree to which subjects’ decisions were modified by the presence of irrelevant 
alternatives. By contrast, another brain area, the dorsal anterior cingulate (ACC), is able to track the 
average values of several possible alternative choices. The ACC appears to code for the value of 
switching away from taking the current default choice in a manner that is predicted by theories of 
optimal foraging in behavioural ecological investigations. In addition we show that the same ACC region 
tracks dynamic changes in how risk prone or risk averse a person should be. Again such tracking is 
predicted by models of optimal foraging in behavioural ecological investigations.