How does our brain choose pleasure over pain?

Roar with pain or pleasure? If we would all be more inclined to lean towards the second option, what mechanism is engaged in our brain to convince us to make such a decision? In an attempt to answer this question, American researchers have studied information processing centers in the cerebral cortex of mice. They thus identified how different groups of neurons share the processing of signals linked to positive and negative information. The results of their research were published on Tuesday December 31 in the journal Neuron. Ultimately, these discoveries could improve the understanding of the brain of people with mental disorders.

Mice have two groups of neurons, located in an area of ​​the brain called the ventral pallidum, which send opposite signals, respectively, into the brain circuit responsible for processing motivation. In order to understand their mechanism, researchers from the Cold Spring Harbor Laboratory (CSHL) have trained animals to associate certain sounds with a sip of water (reward) or an unpleasant breath of air (punishment).

Then, using tools allowing them to monitor very precisely the activity of each brain cell, they observed that activity in the brain in different situations. They discovered that neurons using the neurotransmitter GABA to inhibit activity in the reward circuit were very active in motivating mice to seek water. On the contrary, the neurons that use the neurotransmitter glutamate were activated to avoid air punishment.

Understand if this activity is disrupted in patients with mental disorders

The researchers then confronted the mice with more complex situations where they could receive both punishment and a reward. There, the two sets of neurons reacted and the animals made different decisions in response to the combined stimuli. Those who were thirsty were more likely to risk a breath of air to drink than those who had just received water.

On the other hand, if the researchers artificially shifted the balance of activity in ventral palladium, the behavior of the animals would have been modified. Thus, balancing the signals that inhibit or excite neurons in this area of ​​the brain seems essential to controlling an animal’s motivation, the researchers note. “The balance of activity between these two groups determines whether a mouse will seek a pleasant experience or rather avoid a negative one, depending on the situation in which it finds itself,” explains the study’s lead author, the Professor Bo Li, in a press release issued by the CSHL.

Now researchers want to understand if this activity is disrupted in patients with psychiatric disorders. “Behavioral changes in people with depression or anxiety caused by stress can be caused by changes in this circuit,” says Bo Li. For example, people with depression sometimes stop doing things that are difficult for them. used to provide pleasure, while anxiety patients will tend to take more pains to avoid potential threats.

800,000 suicide deaths worldwide each year

Depression is a common mental disorder that affects 300 million people worldwide, according to WHO. It differs from transient and punctual mood swings in duration and intensity. It can then become a serious illness leading in the worst case to suicide (800,000 cases each year). And, despite various treatments available to combat this affliction, less than half of those affected worldwide benefit from it. The cause: a lack of resources, the shortage of caregivers, the social stigma linked to the disease and sometimes the difficulty in diagnosing it.

Anxiety disorders include various disorders linked to excessive anxiety that are difficult to manage. They can manifest themselves in acute panic attacks or phobias. It is estimated that generalized anxiety disorder affects 2 to 6% of adults. As with depression, women are more affected.

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