'Haven't my neurons seen this before?'

The world grows increasingly more chaotic year after year, and our brains are constantly bombarded with images. A new study from Center for the Neural Basis of Cognition (CNBC), a joint project between Carnegie Mellon University and the University of Pittsburgh, reveals how neurons in the part of the brain responsible for recognizing objects respond to being shown a barrage of images. The study is published online by Nature Neuroscience.

The CNBC researchers showed animal subjects a rapid succession of images, some that were new, and some that the subjects had seen more than 100 times. The researchers measured the electrical response of individual neurons in the inferotemporal cortex, an essential part of the visual system and the part of the brain responsible for object recognition.

In previous studies, researchers found that when subjects were shown a single, familiar image, their neurons responded less strongly than when they were shown an unfamiliar image.

However, in the current study, the CNBC researchers found that when subjects were exposed to familiar and unfamiliar images in a rapid succession, their neurons — especially the inhibitory neurons — fired much more strongly and selectively to images the subject had seen many times before.

“It was such a dramatic effect, it leapt out at us,” said Carl Olson, a professor at Carnegie Mellon. “You wouldn't expect there to be such deep changes in the brain from simply making things familiar. We think this may be a mechanism the brain uses to track a rapidly changing visual environment.”

The researchers then ran a similar experiment in which they used themselves as subjects, recording their brain activity using EEG. They found that the humans' brains responded similarly to the animal subjects' brains when presented with familiar or unfamiliar images in rapid succession. In future studies, they hope to link these changes in the brain to improvements in perception and cognition.

Co-authors of the study include Travis Meyer of Carnegie Mellon and the CNBC, and Christopher Walker and Raymond Cho of the Department of Psychiatry at Pitt. The research was funded by the National Institutes of Health's National Eye Institute and National Institute of Mental Health (R01 EY018620, P50 MH084053, K08 MH080329), and the Pennsylvania Department of Health's Commonwealth Universal Research Enhancement Program.

About Carnegie Mellon University:

Carnegie Mellon is a private, internationally ranked research university with programs in areas ranging from science, technology and business, to public policy, the humanities and the arts. More than 12,000 students in the university's seven schools and colleges benefit from a small student-to-faculty ratio and an education characterized by its focus on creating and implementing solutions for real problems, interdisciplinary collaboration and innovation. A global university, Carnegie Mellon has campuses in Pittsburgh, Pa., California's Silicon Valley and Qatar, and programs in Africa, Asia, Australia, Europe and Mexico.