You’re probably blinking right now, and you don’t even know it. The average person blinks up to 20 times a minute, up to 1,200 times per hour and up to 28,800 times a day. We spend about 10% of our waking hours with our eyes closed—yet we barely even notice ourselves doing it, much less that everything’s gone dark for those 400 or so milliseconds where light is shut off from the retina.
In the past, neuroscientists suggested that the solution might be in the brain—that it somehow maintains a “snapshot” that bridges these very short gaps. These in turn allow us to “observe” a stable picture of our environment without any flashes of darkness. In a new, small study published in Current Biology, researchers Caspar Schwiedrzik and Sandrin Sudmann attempt to explain where in the brain this might take place—and whether the solution might be found in the medial prefrontal cortex. This is located directly behind the forehead in the frontal lobe, and known to play an important role in short-term memory and decision-making.
To test their hypothesis, the neuroscientists implanted electrodes in the heads of six epilepsy patients to monitor activity in different parts of their brain. They showed the participants two randomly allocated dot lattices: a rectangular one and a hexagonal one, each of which was angled in a number of different orientations. These lattices were ambiguous—whether they look as though they are the same way up depends on your perception. The patients were then asked to report whether the lattices appeared to be oriented at the same angle by clicking on a mouse.
When the patients perceived a match, they used their perceptual memory—what researchers believe the brain uses to reconstitute an image of the world around us when we blink—to make that assessment. At the same time, their neural activity in the medial prefrontal cortex spiked up into the “high gamma frequency band,” oscillating at 70 to 150Hz (40Hz is typical). When they didn’t perceive a match, and didn’t need to use their perceptual memory, this activity was far less significant. A further clue came in the form of a subject who had had a section of the superior frontal gyrus removed due to an earlier illness, leaving her unable to store the visual information necessary to answer their questions.
All this might not reveal why everything doesn’t disappear when we blink, but may show where the process takes place. So next time you blink, you can likely thank your prefrontal cortex for keeping the world in place—though there’s a good chance you won’t even notice it happening.
This story has been updated with further details of the study’s methodology.