CommentaryRisky Dopamine
Section snippets
Reward Risk
Behavioral choices are made between economic, motivational, or affective values of outcomes. Decision makers have the tendency to maximize value. Thus value constitutes the final variable determining behavioral choices. Assessment of choice preferences by psychometric tests suggests that the value is subjective rather than objective (physical). Subjective value is called utility or prospect in behavioral economics (although these terms require specific conditions to be fulfilled that are rarely
Risk Influence on Subjective Value
The terms risk avoidance and risk seeking indicate that risk affects behavioral choices. A likely mechanism involves an influence of risk on subjective value, which mediates the influence on reward choices. There are many reasons for these risk attitudes. Risk-avoiding and risk-seeking individuals, respectively, may hate the insecurity of risky outcomes or just love it. Individuals usually value the same rewards higher with small outcomes than with large outcomes or do the opposite (“do not
The Current Data: Risk and Dopamine
There are no sensory receptors for reward value, which is an abstract notion derived from behavioral preferences. As an internal construct of the brain, it may be subjective and not linearly reflect objective value, which is often difficult to assess. Typical reward structures code value, such as dopamine neurons (2) and orbitofrontal cortex (3, 4). However, positive evidence for subjective as opposed to objective reward value coding has been surprisingly difficult to obtain without involving
Extensions
Current evidence suggests that dopamine neurons code reward value in a graded manner (2). It would now be interesting to find the source of the influence of risk on the observed dopamine concentration changes. First, dopamine neurons code also reward risk, although at different trial epochs (8). Might the dopamine risk signal lead to dopamine release in nucleus accumbens, which might affect the dopamine release by the value signal? Second, neurons in orbitofrontal cortex code risk distinctly
Value Coding During Choices
The study by Sugam et al. (1) sheds additional light on dopamine responses during actual choices. If dopamine neurons respond to reward-predicting stimuli, how would their responses reflect two simultaneous stimuli? Would they code the mean reward predicted by both stimuli and thus conform to the Pavlovian actor-critic value coding of reinforcement theory, would they code the maximum reward predicted by the stimuli according to Q learning, or would they code the reward predicted by the stimulus
References (10)
- et al.
Phasic nucleus accumbens dopamine encodes risk-based decision-making behavior
Biol Psychiatry
(2012) - et al.
Coding of reward risk distinct from reward value by orbitofrontal neurons
Neuron
(2010) - et al.
Adaptive coding of reward value by dopamine neurons
Science
(2005) - et al.
Neurons in the orbitofrontal cortex encode economic value
Nature
(2006) - et al.
Orbitofrontal cortex encodes willingness to pay in everyday economic transactions
J Neurosci
(2007)