Multiple dopamine signals

Multiple functions

Large movements engaging plenty of muscles and sensory receptors in monkeys are associated with heterogeneous dopamine increases or decreases at various task events (left). Similar dopamine changes occur in rodents during their behavioural engagement (bottom) These dopamine activities seem to reflect general behavioural activation rather than intercorrelated specific movement parameters or reward expectation. By contrast, more restricted behavioural activity fails to affect dopamine impulse activity in monkeys (right). Thus, dopamine neurons show at least two types of behavioural relationships (top): fast phasic reward prediction error (RPE) signalling, and slower behavioural activation with trial start, movement (and associated visual and somatosensory stimulation), reward consumption and everything that excites the animal.

Response components

Neuronal responses to external events can have multiple components (center), as shown in frontal cortex (top left). An external reward is registered in the brain first by its physical impact and then by its value. Dopamine responses show similar two components (right). Their first component reflects salience and is enhanced by several factors, which explains some non-reward responses (blue box). The benefit is early reward detection (maroon box).

Aversive stimuli

Like rewards, punishers have multiple components that are processed separately (top left). Following psychophysical value assessment (bottom left), a stronger punisher elicits a weaker dopamine excitation, indicating that the excitation reflects punisher salience rather than negative outcome value (top right). Thus, punishers elcit two-component dopamine responses similar to rewards (bottom right). Without such controls, an apparent dopamine excitation from a punisher may simply reflect the first, salience component.