In humans, the thalamus sits deep inside the brain just above the brainstem, yet straddling both hemispheres. This ideal position allows the walnut-size information hub to transmit signals among multiple brain regions. While the mediodorsal thalamus (middle-upper section) is known to be involved in decision-making, a new study confirms the region’s specific responsibility in swiftly updating information as we learn.

In particular, say the Oxford University and Imperial College researchers, this brain structure supports adaptive decision-making, our negotiation of changing situations, such as walking down a busy street or driving a car.

Adaptive Decisions

How exactly do we make the frequent, seemingly “unthinking” decisions necessary to maneuver through our familiar worlds? Generally, we use a strategy based on our past explorations, where we sampled and evaluated available options. Moving to a new home, we soon decide on routes to get to work during rush hour or off-hours, so if construction blocks a familiar path, we can change our minds in the moment to take the best option. Real-world feedback shapes even our most habitual decisions.

The orbital and prefrontal cortex help us make use of feedback in changing situations, though how our brains process the relevant information across these brain networks is still unclear, say Dr. Anna Mitchell and her research team. The mediodorsal thalamus is interconnected with the prefrontal cortex, receives input from the amygdala (part of the pleasure system) and ventral striatum (part of the reward system), plus it contributes to many reward-guided learning and decision-making tasks. This brain structure, then, is a prime candidate for helping to coordinate adaptive decision-making.

“Previously, work from my lab has shown that the mediodorsal thalamus has a role in supporting how the brain learns new information, although interestingly it does not have a role in recalling previously (learned) information,” Mitchell told Medical Daily in an email.

To further explore this brain structure, Mitchell and her colleagues taught Rhesus macaque monkeys tasks on touchscreen computers that released food rewards whenever the monkeys learned new information and made good choices. Generally, the monkeys would persistently choose an option once they learned they’d be rewarded for that choice. Yet when the familiar option no longer rewarded them, the monkeys were able to adapt and choose an alternate, more rewarding option.

Next, the researchers performed an operation on three of the monkeys so that they were unable to use their mediodorsal thalamus. Seven monkeys remained untouched in order to function as experimental controls. Then, the team repeated the computer tests with all of the monkeys. What did they observe?

The three monkeys lacking use of the mediodorsal thalamus struggled to make new choices to maximize their rewards. And, when presented with several differently rewarded options, the same monkeys grappled with their decisions. Though the researchers had assumed the monkeys would just repeat their first choice, instead, they found the monkeys were capable of making different choices, but their ability to quickly integrate information appeared compromised.

The study is limited both in size and because it has not been tested on humans. Still, the experiment demonstrates the fundamental role played by the mediodorsal thalamus in the brain’s ability to swiftly integrate new information when learning or making decisions. Future studies will look at how this region interacts with other areas of the brain.

“We need to investigate how different brain structures within these networks work together with each structure adding something else to the final outcome,” said Mitchell, adding that this knowledge will help us “understand how the normal brain works and what might be going wrong in people who can no longer make decisions or have problems making the optimal decision given all the information that is available to them.”

Source: Chakraborty S, Kolling N, Walton ME, Mitchell AS. Critical Role for the Mediodorsal Thalamus in Permitting Rapid Reward-Guided Updating in Stochastic Reward Environments. eLife. 2016.