Mental Health

Decision-Making Process: Optogenetics Uncover Brain Network Involved In Emotional Choices

During approach-avoidance conflicts, our brains access a specialized network involving the striosomes to help us make difficult and emotional decisions. Photo courtesy of Shutterstock.

You need more money, so you want a high-paid job, yet you know that would mean lots of hard work and probably late nights and weekends, too. Whenever a goal is both desirable and disagreeable, we experience a psychological conflict known as approach-avoidance. During these conflicts, our brains access a specialized network that helps us make difficult and emotional decisions, say MIT neuroscientists. This neural circuit begins and ends with striosomes.

What exactly are striosomes? These cell clusters are distributed through the striatum — a large brain region beneath the cerebral cortex that is involved in coordinating our movements to our motivations. Yet, striosomes are so small and lie so deep inside the brain, researchers find it difficult to image them with an fMRI. For this reason, they remain an undiscovered territory of the brain.

Previous studies from the lab of Dr. Ann Graybiel, an MIT professor and member of the McGovern Institute for Brain Research, identified regions of the brain’s prefrontal cortex that project to the striosomes. Because these regions helped process emotions, the researchers suspected the entire brain circuit might be related in some way to emotion. Importantly, in monkeys, decisions made during approach-avoidance conflicts selectively activate a subset of neurons in a medial prefrontal region that appears to correspond to the human zone targeting the striosomes.

Wanting to better understand this circuit and its function, the MIT team designed a series of experiments.

Discovering the Brain

The researchers studied rats as they performed five different types of behavioral tasks. The rodents’ choices were relatively simple in four of the settings, yet in one, the researchers constructed a more complex approach-avoidance scenario. During this maze-running task, the rats had to choose between two options: one that included strong chocolate (which they like) and a bright light (which they don't like) and another option with dimmer light but weaker chocolate.

If we humans were to confront a similar approach-avoidance choice, we most likely would experience anxiety, which would influence our "cost-benefit analysis" and ultimately influence our decision.

Observing the response of the rats, the researchers added another dimension to these five revealing tasks. During some of the maze runs, the scientists turned cortical input to the rats’ striosomes on and off by shining light directly on the cortical cells — a neuromodulation method known as optogenetics.

By illuminating the rats’ decision-making processes, the researchers discovered the circuit connecting the cortex to the striosomes played a role during the approach-avoidance task, but in the four other tasks, the striosomes did not influence the decision-making process at all.

These findings suggest the striatum (and the striosomes in particular) may act as a mental gatekeeper, the researchers say. The striosomes absorb sensory and emotional information coming from the cortex and then integrate it to produce a decision.

This same circuit appears to include the substantia nigra, a midbrain region which has dopamine-containing cells. When activated by the striosomes, the researchers speculate, these substantia nigra cells produce a long-term effect on decision-making attitudes.

Ultimately, this research suggests new possibilities for relieving anxiety and other mood or emotional disorders. By better understanding the role of the dopamine-containing substantia nigra cells, the gang from MIT believe they also may learn how to ease the symptoms of Parkinson's disease and related disorders.

Source:  Friedman A, Homma D, Gibb LG, et al. A Corticostriatal Path Targeting Striosomes Controls Decision-Making under Conflict. Cell. 2015.