Computation with Dopaminergic Modulation

Definition Dopamine (DA) is a neuromodulator released by midbrain neurons with widespread projections throughout the brain. Dopaminergic modulation has diverse effects on cellular, motor and cognitive functions, including reinforcement learning, working memory and attention. Dysregulation of dopamine also plays a central role in the breakdown of these functions in disorders such as Parkinson's disease and schizophrenia. Detailed Description Dopamine basics DA is a neuromodulator released by neurons in two nuclei of the midbrain: the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNc). The axons of these neurons project to a large number of cortical and subcortical areas. Prefrontal cortex, motor cortex, and the striatum are among the most densely innervated areas. DA release tends to be fairly homogeneous across DA neurons, by virtue of electrical coupling between the axons of adjacent neurons, which induces highly synchronous firing. As pointed out by Paul Glimcher, these properties suggest that DA neurons " cannot say much to the rest of the brain but what they say must be widely heard " (Glimcher, 2011). DA affects its targets primarily by two classes of receptor—D1 and D2—and the distinct properties of these receptors have functional consequences which are discussed below. D2 receptors tend to be activated earlier, and at lower concentrations, than D1 receptors (Lapish et al., 2007; Schultz, 2007). As a consequence, D2 receptors are more sensitive to phasic (transient) DA release than D1 receptors, with the opposite pattern for tonic (background) DA release (Grace, 1991). D1 and D2 receptors also have different postsynaptic effects: D1 receptor activation increases both NMDA (excitatory) and GABA (inhibitory) currents, whereas D2 receptor activation decreases them (Trantham-­‐Davidson et al., 2004).