Looking at a human face triggers activity in our brain unlike any other object

(ORDO NEWS) — It may not be felt, but our eyes are constantly making quick, tiny movements called saccades to take in new information as we focus on different objects in the world around us. In doing so, our brain receives information – and depending on what is the object of our gaze, it turns out that brain activity can be completely unique.

“Although we don’t normally perceive our own eye movements, the abrupt change in visual input with each saccade has significant implications at the neuronal level,” the researchers explain in a new study led by first author and cognitive neuroscientist Tobias Staudigl of the Ludwig Maximilian University of Munich in Germany.

In the experiment, Stowigl and his colleagues worked with 13 patients with epilepsy who had electrodes implanted in their brains to monitor their condition. Such an intervention can be beneficial for brain scientists, so they often approach such patients with electrodes already implanted, in case they want to volunteer their time.

For example, patients agreed to take part in a study in which they were asked to freely view various visual stimuli displayed on a screen, including images of human faces, monkey faces, as well as non-facial images (images of flowers, fruits, cars, and so on).

As they did so, the camera-based eye-tracking system tracked what objects their eyes were looking at, and the electrodes simultaneously monitored neural activity in the amygdala and hippocampus, separate parts of the brain that are involved in various aspects of memory processing, among other functions. the amygdala is also important in regulating our emotions.

Looking at a human face triggers activity in our brain unlike any other object 2

When study participants looked at human faces, neurons between the amygdala and hippocampus fired and synchronized in a pattern that differed from the results obtained with other stimuli, which the team interprets as evidence of how the brain processes memory encoding for important social information, as opposed to other non-social objects.

“It’s easy to argue that faces are one of the most important things we look at,” said study senior author Weli Rutishauser, director of neuroscience research at Los Angeles-based nonprofit medical and research organization Cedars-Sinai.

“We make a lot of very important decisions by looking at faces, including whether we trust someone, whether the other person is happy or angry, whether we’ve seen them before.”

The foundations for these decisions have to be laid somewhere, and the researchers say this process can be seen in the rapid adjustment of saccadic eye movements.

Faces have long been known to fire neurons in the amygdala more than other types of stimuli, although the reasons for this have remained unclear.

“One hypothesis is that these signals are transmitted from the amygdala through strong projections to the hippocampus, where they enhance and prioritize hippocampal processing of stimuli with high social and emotional significance,” the researchers write.

“This may help the hippocampus encode memories of meaningful stimuli and events.”

The researchers note that the proportion of cells visually selective for human faces was significantly larger in the amygdala than in the hippocampus, suggesting that the amygdala plays a more important role in identifying social stimuli in the first place.

“We think this is a reflection of the fact that the amygdala is preparing the hippocampus to receive new socially relevant information that will be important to remember,” Rutishauser says.

Another important discovery was that in the presence of social stimuli, long-range communication between different parts of the brain increased.

“When fixation on a human face followed a saccade, the neural connection between the amygdala and the hippocampus was enhanced,” the researchers wrote. “The same effect was not observed with saccades and fixations on other stimuli.”

However, when participants looked at human faces they had already seen earlier in the experiment, the pattern of firing of neurons in the amygdala was slower, suggesting that learned and familiar faces do not elicit the same neural firing as new social stimuli.

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