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The activation of face cells in the amygdala depends highly on where you are paying attention (2017-01-31)

Our brains are constantly active, processing a myriad of visual stimuli. Faces are particularly important social stimuli, and, indeed, the human brain has networks of neurons dedicated to processing faces.

New research from Caltech now shows that the activation of face cells depends highly on where you are paying attention—it is not enough for a face to simply be within your field of vision. The findings may lead to a better understanding of the mechanisms behind social cognitive defects that characterize conditions such as autism.

The research was conducted in the laboratories of Ralph Adolphs (PhD '93), Bren Professor of Psychology and Neuroscience and professor of biology, and collaborator Ueli Rutishauser (PhD '08) of Cedars-Sinai Medical Center in Los Angeles and a visiting associate in biology and biological engineering at Caltech.

The researchers focused on face cells in a particular region of the brain called the amygdala.

"We know that a damaged amygdala can result in profound deficits in face processing, especially in recognizing emotions, but how amygdala neurons normally contribute to face perception is still a big open question," says Juri Minxha, a graduate student in Caltech's computation and neural systems program and lead author on the paper.

When a face cell responds to a stimulus, it fires electrical impulses or "spikes." By working with patients who already had electrodes implanted within their amygdalae for clinical reasons, the group measured the activity of individual face cells while simultaneously monitoring where a subject looked. Subjects were shown images of human faces, monkey faces, and a variety of other objects such as flowers and shapes. This study is the first in which subjects were free to look around at various parts of a screen and focus their attention on different things.

The study found two types of face cells: those that fire more spikes when the patient is looking at a human face and those that fire a few spikes when the patient is looking at a face of another species (in this case, that of a monkey). Neither type of face cell fired when the subjects were paying attention to objects that were not faces, even if those objects were near a face in the image.

The studies showed that when the monkey and human subjects were viewing images of the same species, the monkeys' face cells reacted about one-tenth of a second more quickly than the face cells of humans, validating a long-standing hypothesis that face cells in monkeys would respond more quickly than corresponding cells in humans. The tenth-of-a-second difference is larger than what can be explained by variation in human and monkey brain size, leaving open the question of why human face cells have a delayed response.

For more information
Cell Reports
Fixations Gate Species-Specific Responses to Free Viewing of Faces in the Human and Macaque Amygdala
Juri Minxha, Clayton Mosher, Jeremiah K. Morrow, Adam N. Mamelak, Ralph Adolphs, Katalin M. Gothard, Ueli Rutishauser

Caltech - California Institute of Tecnology