How smell can affect decision making

We all remember and quickly recognize those very special smells from our childhood or adolescence: grandparents' candy, parents' cake, wet earth after the rain when we were with our gang in the mountains, the sea… And when we remember them, the memory brings back many images, feelings and thoughts that we might think we had forgotten. Our behavior changes temporarily, depending on whether we associate those smells with pleasant or unpleasant sensations.

The sense of smell allows us to detect the presence of volatile substances through cells connected to the limbic system, among other areas of the brain. This structure consists of several groups of neurons responsible for emotions, such as the amygdala; Reward sensations, such as the striatum; and memory management, such as the hippocampus. For this reason, smells have a direct relationship with memories, especially those that have an emotional charge.

In nature, understanding and integrating sensory stimuli through appropriate behavioral responses is essential for survival. In the case of smells, it is not enough for the animal to detect the smell. He must also be able to give it meaning. In other words, understanding what it means for their survival – for example, detecting potential predators and other threats – and what it means for their vital functions such as feeding or reproduction. Finally, he must be able to act accordingly.

Should we go or not?

Neuroscientist Diego Restrepo and his collaborators, from several American and Brazilian universities and research centers, have analyzed the brain mechanisms that allow odors to be associated with simple behaviors, specifically making the decision to act, or alternatively, not to act. They also published in the magazine Current biologyThere is a neural circuit in the hippocampus, which is the area of ​​the brain that allows you to manage memories, and which quickly responds to odors according to previous experiences and circumstances to make the decision you end up making.

The study was conducted on mice. Although there are differences between the sense of smell of these animals and humans, the results can be extrapolated to some extent to our species. Mice have many more olfactory receptors than we do, so they have much greater olfactory sensitivity, are better at distinguishing between very similar odors, and can detect much weaker odors. The role of smells in their daily lives is much more important than that of humans, which also facilitates the study of brain mechanisms associated with them.

The experiment conducted by the researchers is simple in theory. They trained mice to respond to specific odors. The smell of the fruit told them that they would immediately find sugared water in the trough. On the other hand, the smell of mineral oil told them that if they tried to drink at that time, the sugar water would take some time to reach the sink.

In other words, the type of smell they noticed directly influenced the decision to act quickly or not to act at that moment, depending on their previous experience. In English the expression is used Go don't go To describe these mutually exclusive behaviors.

Meanwhile, the scientists scanned the mice's brain activity using a technique called two-photon calcium imaging, which makes it possible to detect neural activity very sensitively and in real time. This is based on the fact that many neurons use calcium as a signal for their activity. When a nerve cell is activated, calcium enters it.

Smell and learning

This observation made it possible to discover a group of interconnected neurons in the hippocampus, whose activation, in response to different odors, is directly related to the behavioral response of mice, i.e. drinking on the spot (He goes)or wait(I do not go).

These neurons are part of the so-called hippocampal CA1 cells, which are known to be involved in the formation of new memories and long-term storage, in spatial processing and navigation in the environment, and in the integration of information to generate a coherent network. Representation of environment, experiences, and mood regulation as a function of stress.

As the authors of this work concluded, the differential activation of CA1 hippocampal neurons depending on odor and previous experiences allows behavior to be directly linked to previous learning, all together with influences on the “act or not to act” decision the mice take.

Despite the above-mentioned differences between the olfactory system of these rodents and humans, the results can be extrapolated to some extent to humans. Although the authors of this study do not say so in their work, in terms of education, the smells that children and adolescents feel during their training and when they learn new things can ultimately influence the decisions they make in the future.