Abstract
The latest animal neurophysiology has revealed that the dopamine reward prediction error signal drives neuronal learning in addition to behavioral learning and reflects subjective reward representations beyond explicit contingency. The signal complies with formal economic concepts and functions in real-world consumer choice and social interaction. An early response component is influenced by physical impact, reward environment, and novelty but does not fully code prediction error. Some dopamine neurons are activated by aversive stimuli, which may reflect physical stimulus impact or true aversiveness, but they do not seem to code general negative value or aversive prediction error. The reward prediction error signal is complemented by distinct, heterogeneous, smaller and slower changes reflecting sensory and motor contributors to behavioral activation, such as substantial movement (as opposed to precise motor control), reward expectation, spatial choice, vigor, and motivation. The different dopamine signals seem to defy a simple unifying concept and should be distinguished to better understand phasic dopamine functions.
Highlights
The question “What is dopamine doing?” keeps stubbornly popping up after the discovery of the brain’s dopamine system and its relationships to Parkinson’s disease, psychosis, and drug addiction
The ensuing research efforts revealed an amazing array of heterogeneous functions at various time courses and levels of specificity that range from general behavioral activation to precise reward signaling for biological learning, machine learning, and economic choice[1]
Despite all the caveats, optogenetics may have uncovered groups of dopamine neurons that are truly activated by specific punishers and differ qualitatively from reward-processing dopamine neurons[45], after 40 years of trying to nail them
Summary
The question “What is dopamine doing?” keeps stubbornly popping up after the discovery of the brain’s dopamine system and its relationships to Parkinson’s disease, psychosis, and drug addiction. In analogy to other neuronal systems, show an early unselective activation, which reflects sensory detection of the stimulus[32] and constitutes a default signal for any potential reward in the environment; it is quickly replaced, before any behavioral action, by the subsequent prediction error component that codes reward value[19,33,34,35]; recent studies confirm this notion[36]. Despite all the caveats, optogenetics may have uncovered groups of dopamine neurons that are truly activated by specific punishers and differ qualitatively from reward-processing dopamine neurons[45], after 40 years of trying to nail them If so, they might be parts of an ancient system detecting fear (of air puff, intense sound, foot shock, and novelty) rather than disgust (quinine)[44] and contrast with the abundant reward-coding dopamine neurons that are depressed by aversive stimuli and code outcome value monotonically from negative to positive[39,44]. We should invest substantial portions of our wealth into all fields of neuroscience
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