McGovern Institute researchers find that the brain starts to register gender and age before recognizing a face.

Sabbi Lall | McGovern Institute for Brain Research

Our brains are incredibly good at processing faces, and even have specific regions specialized for this function. But what face dimensions are we observing? Do we observe general properties first, then look at the details? Or are dimensions such as gender or other identity details decoded interdependently? In a study published in Nature Communications, neuroscientists at the McGovern Institute for Brain Research measured the response of the brain to faces in real-time, and found that the brain first decodes properties such as gender and age before drilling down to the specific identity of the face itself.

While functional magnetic resonance imaging (fMRI) has revealed an incredible level of detail about which regions of the brain respond to faces, the technology is less effective at telling us when these brain regions become activated. This is because fMRI measures brain activity by detecting changes in blood flow; when neurons become active, local blood flow to those brain regions increases. However, fMRI works too slowly to keep up with the brain’s millisecond-by-millisecond dynamics. Enter magnetoencephalography (MEG), a technique developed by MIT physicist David Cohen that detects the minuscule fluctuations in magnetic fields that occur with the electrical activity of neurons. This allows better temporal resolution of neural activity.

McGovern Institute investigator Nancy Kanwisher, the Walter A Rosenblith Professor in the MIT Department of Brain and Cognitive Sciences, and postdoc Katharina Dobs, along with their co-authors Leyla Isik and Dimitrios Pantazis, selected this temporally precise approach to measure the time it takes for the brain to respond to different dimensional features of faces.

“From a brief glimpse of a face, we quickly extract all this rich multidimensional information about a person, such as their sex, age, and identity,” explains Dobs. “I wanted to understand how the brain accomplishes this impressive feat, and what the neural mechanisms are that underlie this effect, but no one had measured the time scales of responses to these features in the same study...”

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