How the brain uses memories to make a survival decision
One forms what is known as a danger or "fear" memory as one progresses through life. Experts are on the lookout for the neural pathways in the brain that are responsible for making decisions or choices.
In terms of survival, it is essential to make effective, efficient decisions that lead us to obtain the reward and achieve the most beneficial goal according to a cost-benefit analysis, which is carried out relatively quickly.
To understand this brain process, Francisco Sotres Bayón, from the Institute of Cell Physiology (IFC) of the UNAM, together with his team of collaborators, are conducting research to explain "how the brain uses emotional memories to guide survival decisions".
While participating in the International Seminar on Neurosciences and Addictions, of the Cannabinoids Laboratory, of the Faculty of Medicine of the National University, he exemplified that when choosing between eating a hamburger or a pizza we take into account a series of variables: which one is fresher, of better quality, which one has more or fewer carbohydrates, fats or proteins, which one is healthier, which one is sold in the cleanest place, etcetera. Considering this number of elements could delay the decision-making process.
To do this quickly and efficiently, our brain evokes memories of previous experiences; for example, "we immediately remember that on one occasion the hamburger was bad for us, and we opted for pizza. In the lab, we study what happens in the brain when we make advantageous decisions that depend on evoking memories".
We focus on creating animal models where we evaluate decision-making guided by emotional memories: the example cited refers to those associated with flavors, but the research also uses environmental stimuli, such as sound or light, he said. Likewise, in the laboratory, they developed novel animal models to evaluate the active suppression of fear in rodents, in particular, that which involves crossing a dangerous area to obtain food.
This animal model, "which we recently validated using an anxiolytic commonly used in humans (Valium), is the first to directly assess immediate and active fear suppression," stressed the scientist. In addition, it has the potential to help us better understand how the brain makes decisions based on cost-benefit calculations in health and disease in humans.
To carry out their research, the scientific team plays with "those memories that we somehow implant in the brain of rodents from training them, that we can evoke and make different manipulations to try to understand what are the brain circuits related to the choices we make every day and that occur in nature," he said.
At the brain level, a memory is created almost immediately and lasts for life, called a danger or "fear" memory, which has a negative valence but triggers defense responses to a threat. One of the parts that are consistently involved in this process is the amygdala. But it is not only that region that is linked in negative valence; it is a brain circuit.
In contrast, there are mechanisms associated with assigning a positive valence to environmental stimuli; in that case, it is a reward memory.
It is well known how both types of valences are assigned; that is, how memories of reward and danger are created, "but they have been studied primarily separately, in isolation, when in fact this is not usually the case". They occur simultaneously, in a dynamic, complex environment, where decisions are made moment by moment, for example when a zebra decides to approach a river to quench its thirst, even though its predators are there.
We seek, he said, to manipulate and record brain activity during motivational tasks and to quantify survival behaviors in rats. To do this, different neuroscience tools are used, such as inactivating different regions of the brain with drugs, evaluating how much a protein that signals the recent activation of a certain part of the brain was expressed, and so on.
The university professor and his team of collaborators found that by decreasing neurogenesis (generation of new neurons), the brain circuit that expresses fear is activated; but by increasing the formation of new neurons, the circuit involved in extinguishing fear acquires greater weight. "In this experiment, by manipulating neurogenesis, we were able to make one circuit predominate over the other," said the IFC member.
They also found that one structure that directly correlates with defense behavioral activity is the lateral habenula, which has received more attention because it signals some aversive events and is implicated in animal models of addiction. "It is a brain region that appears to be very important in regulating the balance between 'good' and 'bad'."
It is a relatively small "chunk" of the brain located above the thalamus and connected to numerous regions involved with the regulation of positive and negative valence stimuli; it is also involved in regulating the activity of serotonin and dopamine, neurotransmitters with a wide range of functions.
Thus, neurons in the habenula can signal both an aversive and an appetitive event. "It appears to have the ability to perform computations involving the integration of information, good and bad."
By silencing this part of the brain with a drug temporarily, they found that inactivating it before conditioning (or learning), has no impact on the task of regulating danger-safety in animal models.
The studies aim to understand how fear is actively suppressed, at a specific time, to obtain a reward, since it can lead to understanding mental conditions, such as anxiety and post-traumatic stress, as well as addiction, even depression, where positive or negative valences are affected, concluded Sotres Bayón.