An unknown neural mechanism involved in habit formation has been uncovered after monitoring dopamine release in rats.
A novel test custom-designed for rats in a study by Ingo Willuhn and researchers from the Netherlands Institute of Neuroscience (Amsterdam), has challenged the accepted knowledge of the underlying dopamine signaling mechanisms that lead to habit formation.
Habits, whether good, bad, or annoying, are behaviors that become automatic routines without using the decision-making region of the brain. Whilst this fundamental behavior is attributed to dopamine signaling, there are many questions yet to be answered, regarding how this signaling changes over time and which neurological pathways are most critical.
Dopamine signaling dysregulation has previously been related to psychiatric behavioral disorders including addiction, attention-deficit/hyperactivity disorder, and obsessive-compulsive disorder. Improving our understanding of the dopamine pathways involved in habit formation; therefore, provides an insight into these conditions can arise.
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Willuhn and his colleagues trained rats over 10 weeks on a seeking and taking task, resulting in habitual seeking behavior. Following training, the team quantified the dopamine levels in the ventromedial striatum (VMS), dorsomedial striatum (DMS), and dorsolateral striatum (DLS), brain regions responsible for motivation, goal-directed behavior and habit learning respectively, in both habitual and control rats.
When compared with control rats, the dopamine levels in the DMS of habitual rats exhibited the completely opposite pattern. At the initiation of the task, dopamine levels were decreased and then increased when completing the task. Signaling in the VMS and DLS were the same between the two groups of rats. By optogenetic stimulation of dopamine neurons in the DMS, Willuhn’s team instantly promoted seeking behavior and habit information.
The results together imply that the temporal dopamine distribution in the DMS, but not VMS or DLS, controls whether or not a behavior is made a habit. By updating our knowledge of these systems, the researchers hope to be able to build on our understanding of these neurological conditions in order to develop better preventative and therapeutic measures.
“It is widely assumed that dopamine signaling ceases once a habit is fully developed”, explained Willuhn. “With this study, we reform the widely accepted theoretical models on dopamine signaling with the finding that striatal dopamine signals neither cease nor shift between regions during habit formation.”
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