Cost-benefit valuation and decision making

How are costs and benefits associated with available options encoded by phasic dopamine transmission in the striatum?

What is the role of integrated frontal-striatal-dopaminergic circuits in choosing one out of several options?

In order to make appropriate decisions, it is imperative that we weigh up both the anticipated costs and expected future benefits of courses of action.  The costs of a course of action may include the associated physical exertion of a response, the time required to achieve a goal or more abstract elements such as the opportunity cost that comes from engaging with one option at the expense of doing something else.  Similarly, the benefits of a decision may be evaluated in terms of the degree to which they provide reward to satisfy current desires or in terms of the information they provide about what the optimal response might be.

It has long been known that certain psychiatric patients or patients with frontal lobe damage can exhibit seemingly contradictory decision making deficits.  For example, frontal lobe patients can sometimes simultaneously seem both impulsive and risk-taking yet also indecisive and apathetic.  We have demonstrated a critical and dissociable role for two frontal regions - the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) (panel A) - in allowing animals to overcome effort (ACC, panel B) or delay (OFC, panel C) costs to gain greater reward.  Further experiments have demonstrated that these functions may be connected with the role of each region in learning about and using associations between actions and outcomes (ACC) or stimuli and outcomes (OFC) to guide decision making.

We have recently been investigating how phasic dopamine transmission in the nucleus accumbens core might be involved in encoding the anticipated costs and benefits of courses of action and how dopamine release relates to animals' subsequent choices.  Nucleus accumbens dopamine has been implicated in energising responses and allowing animals to overcome effort constraints, and the firing rates of midbrain dopamine cells correlate with decision variables such as reward size and delay length.  However, we hypothesised that to play a meaningful role in effort-related computations, accumbens dopamine signals paradoxically should not be modulated by upcoming effort by should simply signal the benefits of choosing a particular course of action.  Once animals had had extended training on the task, this is exactly what we found to be the case.

Current and ongoing research focuses on:

• Electrochemical studies of how costs and benefits are encoded by phasic dopamine transmission in the striatum.

• The role of integrated frontal-striatal-dopaminergic circuits play in enabling us to overcome costs to achieve greater benefits and to resist more easily obtained but lesser rewards.

Selected Key Papers

Reviews:

• Walton ME, Rudebeck PH, Bannerman DM, Rushworth MFS (2007).  Calculating the cost of acting in frontal cortex.  Ann N Y Acad Sci 1104: 340-56.
• Phillips PE, Walton ME, Jhou TJ (2007).  Calculating utility: preclinical evidence for cost-benefit analysis by mesolimbic dopamine.  Psychopharmacology 191: 483-95.
• Walton ME, Kennerley SW, Bannerman DM, Phillips PE, & Rushworth MFS (2006). Weighing up the benefits of work: Behavioral and neural analyses of effort-related decision making.  Neural Netw. 19: 1302-1314

Primary research papers:

• Gan JO*, Walton ME*, Phillips PE (2010).  Differential encoding of costs and future rewards by nucleus accumbens dopamine.  Nature Neurosci. 13: 25-7.(*, these authors contributed equally to this work)
• Croxson PL*, Walton ME*, O’Reilly JX, Behrens TEJ, Rushworth MFS (2009). Effort-based cost-benefit valuation and the human brain. J Neurosci. 29: 4531-41. 
• Rudebeck PH, Walton ME, Smyth AN, Bannerman DM, Rushworth MFS (2006).  Separate neural pathways process different decision costs.  Nat Neurosci. 9: 1161-1168.
• Walton ME, Bannerman DM, Alterescu K, Rushworth MFS (2003). Functional specialization within medial frontal cortex of the anterior cingulate for evaluating effort-related decisions.  J Neurosci. 23, 6475-6490.
• Walton ME, Bannerman DM, Rushworth MFS (2002).  The role of rat medial frontal cortex in effort-based decision making.  J Neurosci. 22, 10996-11003.