Dopamine is a catecholamine neurotransmitter released from the ventral tegmental area (VTA) and substantia nigra in the midbrain. It drives learning through reward prediction error signals and controls working memory maintenance and updating in the prefrontal cortex via D1 receptors. It is also essential for motor program selection in the striatum, directly influencing reaction time and movement accuracy.
Dopamine Pathways and Cognitive Function
Dopamine operates through four major pathways, with the mesocortical pathway (VTA to prefrontal cortex) and mesolimbic pathway (VTA to nucleus accumbens) among those relevant to cognition. The mesocortical pathway is involved in attention control, planning, and working memory maintenance. D1 receptor stimulation in the prefrontal cortex produces an inverted U-shaped dose-response, in which either too little or too much stimulation impairs spatial working memory, and this response has been observed across species.
Reward Prediction Error and Learning
Dopamine neurons encode the difference between expected and actual outcomes, known as reward prediction error. Firing increases when rewards exceed expectations and decreases when outcomes disappoint. This signal drives synaptic plasticity in the striatum, implementing reinforcement learning of behavior.
Motor Control and Performance Impact
Nigrostriatal dopamine controls motor program selection and execution in the basal ganglia. One model explains how the rise and fall of dopamine controls action selection through the segregation of D1 and D2 receptors in direct- and indirect-pathway projection neurons of the striatum. This mechanism of selecting and executing movements is also involved in rapid responses in reaction time tests and cursor control in aim tests.