Dopamine signals in the brain are critical for motivated behavior. However, their regional specificity and the precise information conveyed by dopamine signals is under debate. For a long time, the idea dominated that dopamine encodes a reward-prediction error and that this signal is broadcasted uniformly throughout the brain. As part of the Brainscapes consortium, researchers from the Netherlands Institute for Neuroscience now demonstrate (recently published in PNAS) that this prediction error is restricted to a specific portion of the striatum and that dopamine signals are also otherwise regionally heterogeneous.
Dopamine neurotransmission is pivotal for neuronal processing of, and behavioral responding to, appetitive and aversive stimuli. The dopamine system is thought to be dysregulated in many psychiatric disorders. The largest releasable pool of dopamine is found in the striatum, a large brain nucleus that is the main input structure of the basal ganglia and the primary projection target of midbrain dopamine neurons. The striatum crucially mediates dopamine’s role in motivated behavior. Although it is undisputed that striatal dopamine plays a prominent role in motivated behavior and learning, the precise information content of dopamine signals as such is under active debate.
The researchers found that dopamine release is, regionally, extremely heterogeneous in many aspects and that a prediction error-like signal is predominantly found in the relatively small limbic domain of the striatum. “Despite all heterogeneity, another striking organizing principle is that stimulus valence directs dopamine concentration homogeneously across all regions which means that appetitive stimuli increase dopamine and aversive stimuli decrease dopamine” says Ingo Willuhn, group leader at the Netherlands Institute for Neuroscience.
Willuhn: “Until now both the lack of neuro-measurement tools that can cover all of the relevant pathways, as much as the lack of simultaneous investigation across different regions of the striatum hindered research into the precise information conveyed by dopamine signals”. For the first time, the scientists looked at six regions simultaneously. Using an electro-analytic method, they tracked second-by-second dopamine release in all functionally relevant domains of the striatum of rats across behavioral conditioning.
These findings contribute to unraveling the long-standing question of how regional dopamine in the striatum realizes its many functions.