Monkeys recognize a wide variety of faces thanks to a brain area that specializes in face perception, according to a new study.
A team led by Doris Y. Tsao of Harvard Medical School in Boston used functional magnetic resonance imaging (fMRI) to identify three particularly face-responsive patches of brain tissue in each of two macaque monkeys. The researchers then implanted electrodes in each monkey’s most-active brain area to record responses from a total of 310 neurons.
All but eight of these cells, or 97 percent, responded far more strongly to the sight of faces than to images of patterned grids, fruits, gadgets, or people’s or monkeys’ bodies and hands, Tsao and her colleagues report in the Feb. 3 Science. All sorts of faces elicited notable neural reactions, including human and macaque faces, familiar and unfamiliar faces, and cartoon faces.
The only other images that sparked activity, though weak, in these cells were clock faces and round fruits, which the researchers point out have the general shape of faces.
Intriguingly, brain tissue specialized for face perception was located in one monkey’s left hemisphere and in the other’s right hemisphere.
Earlier electrode studies conducted without fMRI guidance in monkeys indicated that no more than 30 percent of the cells in any brain area preferentially respond to faces.
The researchers plan to study the monkeys’ other face-sensitive areas with electrodes. It’s unclear whether any of these regions correspond to a brain area in people that has been implicated in face perception (SN: 7/7/01, p. 10: Faces of Perception).