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Monday, December 31, 2012

Why do we blink?

Obviously, people blink in order to lubricate their eyes. But that can’t be the only reason. We blink far more often than simple moistening obligations would require. Plus, we seem to blink most at attention break points—at the ends of written sentences or during pauses in speech. This makes sense if you consider that each blink causes a momentary black-out of our visual system. We’re blinking at times when we’ll miss the least amount of information. Or are we looking at things the wrong way around? Researchers led by Tamami Nakano of Osaka University showed that eyeblinks actually cause attention disengagement rather than occurring after we’ve already briefly disengaged.

In particular, the researchers were interested in two regions of the brain: the dorsal attention network, which controls where we focus our attention, and the default-mode network (DMN), which counteracts the dorsal attention network and is involved in introspection. They placed ten healthy volunteers in an fMRI while the subjects watched scenes from a TV show (Mr. Bean). The subjects blinked an average of 17.4 times per minute. They compared brain activity during the spontaneous blinks to activity when the subjects were not blinking and to moments when the screen was physically blacked out for the same duration and frequency as normal eyeblinks.

The scientists found that spontaneous eyeblinks activated the DMN and deactivated the dorsal attention network. This was not true for screen blackouts, which affected the visual areas of the brain, but not the attention allocating areas. This suggests that we blink not because there’s been a break in our attention, but in order to cause that break. Blinking may help us push forward to the next image or line of dialogue.

Nakano T, Kato M, Morito Y, Itoi S, & Kitazawa S (2012). Blink-related momentary activation of the default mode network while viewing videos. Proceedings of the National Academy of Sciences of the United States of America PMID: 23267078.