Neuroscientists reveal that a simple brain region can guide complex exploits of mental activity

Columbia neuroscientists have revealed that a simple brain region, known to treat basic sensory information, can also guide complex feats of mental activity. The new study involving mice has demonstrated that somatosensory cortex cells, the area of ​​the brain responsible for touch, also play a key role in reward learning, the sophisticated type of learning that allows the brain to develop. Associate an action with a nice result. This is the basis on which we connect our work at the office to this paycheck, or this A + to the studies we conducted for the test.

The new research, published today in Cell reports, provides evidence that learning and memory are not relegated to a few selected areas, but can instead penetrate the brain.

"Our brains know how to make links, or badociations, between seemingly disparate information, but the question of where these badociations are recorded has remained an unresolved issue," said Randy Bruno, PhD, principal investigator at Mortimer B. Zuckerman from Columbia. Institute and lead author of the newspaper. "With current research, we have not only seen these badociations form in real time at the level of individual brain cells, but we have also shown that this type of learning occurs in an area of ​​the brain that has not been judged. able to do it. "

Most cells consist of a cell body, but neurons have a more complex form. they have branches that protrude from their bodies. These tree-like branches, called dendrites, can extend from one cell at a time in the thousands, connecting and sending electrical impulses to the dendrites of neighboring neurons.

The organization and disposition of dendrites are particularly intriguing in the somatosensory cerebral cortex. Like a multi-layered cake, it contains six distinct layers. Each layer is a little different.

"Somatosensory cortex neurons are located deep in layers five or six, but their dendrites extend into the upper layer," said Dr. Bruno, also an badociate professor of neuroscience at the College of Physicians and Surgeons Vagelos of Columbia. "The result is a complex network of dendrites that fill the upper layer of the somatosensory cortex, like the canopy of a dense forest."

While monitoring the activity of these dendrites, the researchers trained mice to a simple sensory task. The mice used their whiskers to detect a small perch in a dark room. Once the pole was found, the animals moved a lever that released water as a reward.

"Since this task implied the sense of animal touch, we expected the dendrites of the somatosensory cortex to trigger when the whiskers hit the pole, which they did," said Dr. Bruno . "But during the second part of the task, when the animal received the water reward, these same dendrites fired a second time, which we did not expect."

This observation, which directly linked sensory dendrites to reward learning, was disconcerting. Reward learning is the process by which the brain connects a sequence of actions to a feeling of well-being and is therefore more likely to repeat these actions. Decades of research have shown that it is advantageous to learn to be guided by various brain regions, but the sensory cortex has been the object of little attention.

According to conventional wisdom, the sensory cortex would only relay basic information about an external stimulus, such as whiskers touching a pole. This information is sent to a cortex badociation, which collects and organizes information for further processing in the frontal cortex, one of the most sophisticated regions of the brain.

"Our findings suggest that the brain is starting to learn complex badociations earlier than expected," said Dr. Bruno.

Indeed, when the researchers then removed the mast, the animals trained to this task had another surprise. The somatosensory dendrites of the animals continued to shoot when they received water. On the other hand, water has no effect on neuronal activity in animals that have never learned the task, which shows that it is an acquired badociation.

Regarding why the brain may have evolved to use seemingly simple brain cells for learning purposes, Dr. Bruno proposes to give the brain a way to get a head start.

"Simple badociations can be learned faster and better if primary sensory areas support some of the early work," said Dr. Bruno. "For example, learning that STOP signs are red and have a distinct shape allows you to start braking well before reading the words STOP – an ability that has obvious advantages for survival."

For the future, one of the key unanswered questions is whether a chemical release in the somatosensory cortex is at the root of the feeling of well-being that promotes learning by reward.

"The dopaminergic chemical is the primary factor learning reward in other brain regions, but dopamine is largely absent from the somatosensory cortex," said Dr. Bruno. "There must be another comparable neuromodulator at play, and we are actively exploring it."