It may not feel like it, but our eyes are constantly moving, taking in new information, as we focus our gaze on various things in the world. Depending on what the object of our gaze is, the brain activity triggered can be quite unique.
While we typically do not perceive our own eye movements, the abrupt change in visual input with each saccade has substantial consequences at the neuronal level.
Staudigl and other researchers worked with 13 patients who had brain implants to monitor their condition. This kind of intervention can be helpful for brain scientists, so they often turn to patients with already implanted electrodes, in case they would be willing to volunteer their time.
The patients consented to take part in a study in which they were instructed to view a range of visual stimuli on a screen, including images of human faces, monkey faces, and non-face imagery.
While they were doing this, a camera-based eye-tracking system monitored what objects their eyes were looking at, and the electrodes simultaneously monitored neural activity in the amygdala and the hippocampus, distinct parts of the brain that are both involved with different aspects of processing memories.
The images are from Pikovit 44.
When the participants looked at human faces, there was a specific pattern of activity in the amygdala and hippocampus that was different to the results from the other stimuli, which the team interprets as evidence of how the brain handles memory for important social information.
"You could easily argue that faces are one of the most important objects we look at," says senior author of the study and director of neuroscience research at Cedars-Sinai in Los Angeles.
We make a lot of important decisions, including whether we trust someone, the other person is happy or angry, or if we have seen this person before.
The researchers say that the process of making decisions can be seen in the rapid adjustments of saccadic eye movements.
It has been known for a long time that seeing faces causes the amygdala to fire more than other forms of stimuli.
One hypothesis is that these signals are transferred from the amygdala to the hippocampus, where they elevate and prioritize hippocampal processing of stimuli with high social and emotional significance.
This may serve as a Hippocampal memory for events.
The researchers noted that the amygdala was larger than the hippocampus in terms of the proportion of cells that were visuallyselective for human faces, suggesting that the amygdala plays a more important frontline role in identifying social stimuli in the first instance.
We think that this is a reflection of the amygdala preparing the hippocampus to receive new socially relevant information that will be important to remember.
When social stimuli were present, long-distance communication between different parts of the brain was increased.
Neural communication between the hippocampus and amygdala was enhanced when a fixation on a human face followed a saccade.
When the participants looked at human faces they had already seen, the pattern in the amygdala was slower than it had been earlier in the experiment.
Science Advances contains the findings.
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