Dopamine, the Thermometer and Thermostat of Value

Reward Prediction Error vs Incentive Salience Credit: Wiley

A 2017 article in Scientific American Mind by Maia Szalavitz proposes that associating pleasure with the neurotransmitter dopamine, which plays an essential role in movement and motivation, may be a misunderstanding. Instead, neuroscientist Wolfram Schultz, MD, of the University of Cambridge sees dopamine serving as a standard currency system for desire.

I don’t see dopaminergic neurons acting as a currency of desire because that implies a standard unit of measurement. However, we know the only way our feelings or that which we value is evaluated is via subjective self-report. I hypothesize that for different neural circuits, dopamine acts as a thermometer or indicator of value for the reward prediction error theory and as a thermostat or modulator of value regarding the incentive salience theory.

Values are that what you act to gain or keep and are the motivating power of your thoughts, choices, actions, and a necessity for your survival, psychologically and physically.

Just as a thermometer measures temperature from a state of hot to cold, and its currency is degrees, so your affective systems measure morality from good to evil. Your feelings, in a sense, are decision-making algorithms that evolved to guide behavior toward what was historically most likely to promote survival and reproduction. Thus, your feelings (the simple perceptions of pleasure to pain and calm to stress) are an indicator of moral value.

Terry E. Robinson and Kent C. Berridge, of the Department of Psychology, University of Michigan, set out to test the theory that dopamine produces pleasure. First, the neuroscientists destroyed dopamine neurons in rats to see whether that would deprive them of experiencing pleasure when given sweet foods. The rats would barely even move due to the severe dopamine depletion and had to be fed artificially because they had no motivation to eat or drink anything. Unexpectedly, however, their facial reactions were completely normal, and they continued to lick their lips in response to something sweet while grimacing when given something bitter.

When they increased the dopamine levels in rats using appropriately implanted electrodes, they reversed the findings: the rats did not lick their chops more eagerly when eating, as expected with the “dopamine is pleasure” theory…