Brain Hemispheres Selectively Track the Expected Value of Contralateral Options

Abstract

A main focus in economics is on binary choice situations, in which human agents have to choose between two alternative options. The classical view is that decision making consists of valuating each option, comparing the two expected values, and selecting the higher one. Some neural correlates of option values have been described in animals, but little is known about how they are represented in the human brain: are they integrated into a single center or distributed over different areas? To address this issue, we examined whether the expected values of two options, which were cued by visual symbols and chosen with either the left or right hand, could be distinguished using functional magnetic resonance imaging. The two options were linked to monetary rewards through probabilistic contingencies that subjects had to learn so as to maximize payoff. Learning curves were fitted with a standard computational model that updates, on a trial-by-trial basis, the value of the chosen option in proportion to a reward prediction error. Results show that during learning, left and right option values were specifically expressed in the contralateral ventral prefrontal cortex, regardless of the upcoming choice. We therefore suggest that expected values are represented in a distributed manner that respects the topography of the brain systems elicited by the available options.

Lesion mapping of cognitive control and value-based decision making in the prefrontal cortex

“…S5), consistent with prior studies (42,55). Alternatively, the left-lateralized IGT effect may be due to effector-specific, contralateral value representations in the vmPFC in our mostly right-handed participants (317 of 344) (56).…”

The left hemisphere learns what is right: Hemispatial reward learning depends on reinforcement learning processes in the contralateral hemisphere

“…These findings, together with findings highlighting a crucial role for DA in activational aspects of behaviour Everitt, 1992, 2007), have led researchers to suggest that the impact of motivation on behaviour is mediated by DA (Chakravarthy et al, 2010;Salamone and Correa, 2012;Wise, 2004). Several studies have also shown that the same neural circuitry may also represent the expected value of stimuli presented to one hemifield, but largely restricted to the contralateral hemisphere (Gershman et al, 2009;Palminteri et al, 2009;Wunderlich et al, 2009), suggesting the possibility of unilaterally activating the brain's motivational system. This notion was recently confirmed in a study where unilateral deep brain stimulation of the subthalamic nucleus, a procedure mimicking the impact of DA enhancers, boosted motivational processes within the stimulated hemisphere, as indicated by greater exerted force for the hand controlled by the stimulated hemisphere following increased monetary incentives (Palminteri et al, 2013).…”

“…For example, PEs for actions performed by the right or left hand are predominantly represented in the contralateral ventral striatum (Gershman et al, 2009;Madlon-Kay et al, 2013;Palminteri et al, 2009). Because all effectors used to respond in the present study were controlled by the left hemisphere (i.e.…”

“…Moreover, such models can be used to summarize complex learning behaviours into a few parameters which can be used to link differences in post-learning behaviour to differences in learning processes (Frank et al, 2007). Here, we used a modified version of the classical Q-learning model to account for differences in learning from different hemifields (for similar approaches, see Palminteri et al (2009) and Palminteri et al (2013)). In this modified Q-learning model, each symbol is assigned a value Q i j , which depends on its reward history.…”

“…While incentive motivation can be increased in one hemisphere separately (Palminteri et al, 2013;Schmidt et al, 2010), and the neural representation of reward values for lateralized presented objects are located in the contralateral hemisphere (Gershman et al, 2009;Palminteri et al, 2009;Wunderlich et al, 2009), it remains unclear whether the neural correlates of hemifield-specific incentive motivation are also lateralized. The present results demonstrate that subtle differences in incentive motivation between hemifields, implicating lateralized brain structures during learning (i.e.…”