Data from the paper show a sharp but brief increase in neural activity -- a visually evoked potential -- when a stimulus pattern is shown to a mouse at about 80 milliseconds (bright orange vertical line). Notably when a stimulus is familiar, activity decreases significantly (cooler colors) after that transient increase. Image credit: Bear Lab/MIT Picower Institute.
Because figuring out what is new and what is familiar in what we see is such a critically important ability for prioritizing our attention, neuroscientists have spent decades trying to figure out how our brains are typically so good at it. Along the way they’ve made key observations that seem outright contradictory, but a new study shows that the mystifying measures are really two sides of the same coin, paving the way for a long-sought understanding of “visual recognition memory” (VRM).
VRM is the ability to quickly recognize the familiar things in scenes, which can then be de-prioritized so that we can focus on the new things that might be more important in a given moment. Imagine you walk into your home office one evening to respond to an urgent, late email. There you see all the usual furniture and equipment—and a burglar. VRM helps ensure that you’d focus on the burglar, not your book shelves or your desk lamp.
The findings in the new study, led by MIT Picower Institute's Mark Bear and former Bear Lab postdocs Dustin Hayden and Peter Finnie, explain how visually evoked potentials (VEPs) increase even amid an overall decline in neural response to familiar stimuli. They also explain more about the mechanisms underlying VRM – the momentary increase of a VEP may be excitation that recruits inhibition, thereby suppressing activity overall.
The new evidence suggests that what’s happening is that the VEP is a sign of the activity of the brain quickly recognizing a familiar stimulus and then triggering an inhibition of activity related to it.