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Study Pinpoints Brain Circuitry of Emotional Decision-Making

MIT neuroscientists identify the neural circuitry linked to emotional decisions.

This post is in response to
Tonic Levels of Dopamine Lubricate Moments of Superfluidity
Striatum in red. 
Source: Life Science Databases/Wikimedia Commons

We all know the gut-wrenching feeling of being emotionally torn apart while deliberating to make the right decision in a circumstance where both choices have pros and cons. Until now, the neural circuitry involved in making emotional decisions has eluded brain researchers. Yesterday, MIT neuroscientists unveiled a groundbreaking new discovery that pinpoints the brain mechanics involved in making an emotional decision.

Whenever you make a hard decision, you inherently perform a "cost-benefit analysis" of the pros and cons of each option using pragmatic rationale combined with weighing the emotional consequences. Even though there may be obvious extrinsic rewards linked to one choice, how will this decision affect you psychologically? Will you feel as if you sold your soul to the devil if you do something solely for a material reward or financial gain?

For example, someone could ask him or herself, "Should I take the high paying job overseas that will advance my career but requires leaving my family and the hometown community I adore?" Or, "Should I go to a college that is highly ranked by U.S. News and World Report or trust my gut instincts and go to a less prestigious school where I know I'll be happier and have a more positive learning experience?" Or, “Should I stay in a secure job that I hate just for a weekly paycheck and the habitual rewards of a lifestyle I'm accustomed to or take a risk? I'm dying to pursue my lifelong passion for culinary arts by opening a restaurant, but what if it fails?”

We’ve all been in a situation that required emotional decision-making. When was the last time you had to make a really tough emotional decision? Think back. How did it feel? What was going on in your brain as you were hemming and hawing about the benefits and detriments of an emotional decision? Recently, neuroscientists at the Massachusetts Institute of Technology (MIT) identified neural circuits in the striatum that are directly linked to parts of the brain’s prefrontal cortex and other brain regions that are involved in processing emotions, making emotional decisions, and physical movement.

"Striosome-Dendron Bouquets" Are at the Heart of Emotional Decision-Making

The striatum is a subsection of the basal ganglia, which holds a cluster of various brain regions that are associated with habit formation, control of voluntary movements, emotions, and addiction. According to the MIT researchers, malfunctions of the basal ganglia have been associated with Parkinson’s and Huntington’s diseases, as well as autism spectrum disorders (ASD), obsessive-compulsive disorder (OCD), and Tourette’s syndrome.

The communication pathway to the striatum is directly linked to another complex subsystem that is fueled by dopamine. The researchers call this subsystem a “striosome-dendron bouquet.” The cluster of neurons in this bouquet are involved in making decisions that require any type of anxiety-provoking "cost-benefit analysis" that entails being pragmatic and heeding to your primal gut instincts simultaneously. 

Ann Graybiel, an Institute Professor at MIT and member of the McGovern Institute for Brain Research, was the senior author of the recent study on emotional decision-making. In a statement, Graybiel said that the striosome-dendron bouquet may also be a potential target for treating the neural degeneration seen in Parkinson’s disease.

The September 2016 study, "Striosome–Dendron Bouquets Highlight a Unique Striatonigral Circuit Targeting Dopamine-Containing Neurons,” was published yesterday in Proceedings of the National Academy of Sciences.

Graybiel and her colleagues at MIT were able to pinpoint these neural connections using a revolutionary technique developed at MIT known as “expansion microscopy.” This method enables scientists to expand brain tissue which results in much higher-resolution brain imaging than would be possible using conventional microscopes. Please take a few minutes to watch this YouTube video of Ann Graybiel describing her research at MIT.

Dopamine Drives Emotional Decision-Making and the Movement Required to Follow Through

The brain mechanics of emotional decision making involve a loop–circuit that relies on the function of dopamine to modulate our emotional moods and physical movements. In this study, the MIT neuroscientists were able to identify a specialized subsystem within this feedback loop.

Using novel mouse models and tissue expansion to allow nanoscale imaging, Graybiel et al. demonstrate that striatonigral fibers originating in striosomes (compartments within the striatum) form bouquet-like clusters of dopamine-containing neurons and their ventrally extending, tightly bundled dendrites.

The researchers believe that the stunning selectivity of output from the striatum to these bouquets suggests that the striasom-dendron bouquets can exert powerful and focused control over elements of the dopamine system in both typical and atypical situations.

The dopamine systems of the brain are the prime driving force of movement and motivation. Graybiel's research suggests that striosomes relay information directly to cells within a region of the substantia nigra (black stuff), which is the brain’s primary dopamine-producing center. Dopamine has many functions in the brain, including roles in initiating movement and regulating mood.

Eighty percent of dopamine is produced in the substantia nigra. Its axons are threaded like a sprinkler system throughout the brain, squirting dopamine into pleasure centers, where it causes a neural chain reaction that gives you a hit of ecstasy or reward that can lead to habit formation. Dopamine also facilitates motor learning. Autopsies of people with Parkinson’s disease have shown that the black stuff of the substantia nigra appeared lighter in color. This is one way researchers made the connection between dopamine and the fluidity of movement.

To figure out how all these brain regions might be communicating, Graybiel and colleagues discovered extensive connections between neural clusters of cells in the striatum and dopamine-producing cells of the substantia nigra. The dopamine-producing cells send down many tiny extensions known as dendrites that become entwined with axons which come up to meet them from the striosomes. This forms a bouquet-like structure.

Conclusion: More Research On the Striatum and Decision-Making Is Needed

The recent findings from MIT expand our understanding of how emotional decision-making circuitry encompasses the prefrontal cortex, striosome compartments in the striatum, and a subset of dopamine-producing cells in the substantia nigra.

Together, the researchers believe that the striosomes act as a gatekeeper that absorbs sensory and emotional information coming from the cerebral cortex and integrates this information in a way that helps you decide how best to proceed. Then, the bugle is sounded to "go!" from dopamine-producing cells which results in subsequent actions.

To explore this hypothesis more thoroughly, the MIT researchers plan to study mice in which they can selectively turn the striosome-dendron bouquet on and off in real-time as mice are prompted to make decisions requiring a cost-benefit analysis.

Graybiel and her team also plan to investigate whether these connections are disrupted in mouse models of Parkinson’s disease. Although both MRI studies and postmortem analysis of Parkinson’s patients' brains have shown that the death of dopamine cells in the substantia nigra is strongly correlated with the disease, more research is needed to determine if this subset overlaps with the dopamine cells that form the striosome-dendron bouquets. Stay tuned!

© 2016 Christopher Bergland. All rights reserved.