In a breakthrough that could alter our understanding of movement and control, MIT researchers have discovered new pathways in the brain that manage dopamine release, potentially influencing the way we carry out actions. Led by Ann Graybiel, an MIT Institute Professor and member of MIT’s McGovern Institute for Brain Research, the team found that alongside the well-documented "go" and "no-go" pathways, two additional pathways originating in the striatum—a crucial brain region for coordinating movement—play a role in controlling this process.
As per findings published in Current Biology, these novel pathways have a direct impact on dopamine-producing neurons. One stimulates dopamine release and the other inhibits it, the researchers say. This discovery points to a more complex network of brain signals that not only initiate or suppress movements but also regulate motivation and emotional responses.
Graybiel's team, which includes lead author Iakovos Lazaridis, a research scientist at the McGovern Institute, has spent decades studying the striatum. Their new study builds on previous work that explored how parts of the striatum known as striosomes and the surrounding matrix affect motor control. It has emerged that striosomes, which receive input related to emotion, wield significant influence over dopamine levels by stimulating or inhibiting dopamine release through pathways connected to diverse neurons.
Digging deeper into the structure of the striatum, the study elucidates the interaction between striosomes and the substantia nigra, the brain's main dopamine-producing center. The researchers confirmed that D1-type striosomal neurons directly stimulate the substantia nigra, while D2-type neurons first connect through the globus palladus, an indirect route reducing dopamine output and potentially inhibiting movement. According to a statement obtained by MIT News, Graybiel elucidated, "In the striosomes, we've found what is probably a mimic of the classical go/no-go pathways." She added, "They're like classic motor go/no-go pathways, but they don't go to the motor output neurons of the basal ganglia. Instead, they go to the dopamine cells, which are so important to movement and motivation."
This intricate mapping of the brain's decision-making circuitry can offer fresh perspectives on disorders such as Parkinson's disease, which targets the same brain regions involved in these newly identified pathways. Noted neuroscience professor Sten Grillner from the Karolinska Institute, who was not part of the study, remarked on the significance of the findings. "Clearly, the regulation of dopamine activity is critical in our everyday life with regard to both movements and mood, to which the striosomes contribute," Grillner told MIT News. The research was supported by various institutions, including the National Institutes of Health and the Saks-Kavanaugh Foundation.
Looking ahead, the MIT team plans to delve deeper into the striatal circuitry to better understand how these mechanisms affect actions that carry high emotional stakes, such as those inducing anxiety or stress. The ultimate goal is to isolate the functions of these modules to decode precisely how striosomes modify motor control according to the varying demands placed upon the body and the mind.
