The human brain is likely the most remarkably complex organ known to man. It controls every aspect of our lives, from our sleep and hunger cycles to our ability to speak and communicate. Our defining attribute, however, is our ability to make complex decisions, and scientists are now uncovering the secrets of this ability. One type of decision-making in particular has caught researchers’ eyes: cost-benefit decisions.
Cost-benefit decisions have gray areas, or strong positive and negative elements; for example, choosing to take a higher-paying job in a far away city versus keeping a lower-paying job to stay with family and friends is a cost-benefit decision. Situations that prompt these decisions are called approach-avoidance conflicts, and according to researchers at MIT, these situations generally produce anxiety, which strongly influence choices.
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The part of the brain involved in making these so-called “high risk, high reward” decisions is our prefrontal cortex, an area evolved to specialize in control of movement and emotion. Another area of the brain, the striatum, has also been implicated, as it regulates many of the same functions. What excited researchers, however, was the discovery of striosomes, the so-called “gatekeepers” between these two areas. Not much was known about these mysterious structures, but research is now beginning to uncover their essential role in processing emotion and sensory information during decision making.
Researchers designed a study to further investigate the function of striosomes. They presented rats with different decision-making scenarios, one of them being the approach-avoidance conflict. Rats were offered two options: receive more chocolate (which they liked) and be exposed to a bright light (which they disliked), or receive less chocolate, but be exposed to a dimmer light. This is comparable to the cost-benefit analysis humans perform in their daily decisions.
Image Source: Photography by Peter A. Kemmer
Researchers were surprised that they could manipulate the rats’ reactions by altering their striosomes. By optogenetically stimulating the brain through the striosomes, they found that the rats chose the “low risk, low reward” option more often (less light but also less chocolate). However, when researchers stopped the flow of signals through the striosomes, rats chose the “high risk, high reward” option up to 20% more often than before (more chocolate and more light).
This discovery shed light on the previously unknown importance of striosomes. These structures are important for constructing responses to decision-making situations and for causing anxiety’s influence on our decisions. This outcome has huge implications for the treatment of anxiety disorders, which are now being linked to this area of the brain. Striosomes also contain the substantia nigra, a midbrain cell group important for movement and motivation. Death of these cells causes Parkinson’s Disease. These new discoveries are stimulating efforts to find treatments to previously misunderstood diseases and revolutionizing the way we understand decision-making.
Feature Image Source: Risk Management by Scott Maxworthy
