Blinking Causes Brain To Go Off-Line
Tamami Nakano of Osaka University and colleagues write about their findings in the 24 December online issue of the Proceedings of the National Academies of Science, PNAS.
In earlier work, where they had invited volunteers to watch Mr Bean videos, Nakano and colleagues discovered that people's eyes blink when they need to pay less attention, for instance when the video cuts to a new scene.
And in another study, they found people blink when they pause while speaking, and this entrains their listeners to time their eye blinks to occur a split second later.
This seems to confirm the common-sense idea that we blink at times when we'll miss the least important information.
But in their new PNAS study, Nakano and colleagues appear to show that eyeblinks actively cause attention disengagement, they are not a response to it.
For the study, 20 volunteers watched videos of Mr Bean while the researchers scanned their brains with functional magnetic resonance imaging (fMRI) and also monitored their eyeblinking.
They used Mr Bean videos so the participants would blink spontaneously as they looked at visually stimulating, natural scenes, rather than while observing static images that don't need as much attention.
The researchers compared brain activity during spontaneous eyeblinking to activity when the volunteers were not blinking. They also looked at what happened to brain activity when the video monitor was physically blacked out for the same length of time and frequency of normal eyeblinks.
They found that spontaneous eyeblinks are closely followed by the reciprocal activation of the default mode network, and the deactivation of the dorsal attention network.
"We show that while viewing videos, cortical activity momentarily decreases in the dorsal attention network after blink onset but increases in the default-mode network implicated in internal processing," they write.
The default mode network, also known as the task-negative network, is a cluster of brain regions that become active when we are not observing the outside world but focused on internal reflections: recalling memories, having daydreams.
The dorsal attention network includes regions like the frontal and parietal lobes, which become active when we focus attention on something that is happening in the outside world.
In contrast, this reciprocal activation and deactivation of the two networks did not happen in response to the physical blackouts on the screen, which would suggest that activation of the default network was not a response to a lack of visual input.
"The results suggest that eyeblinks are actively involved in the process of attentional disengagement during a cognitive behavior by momentarily activating the default-mode network while deactivating the dorsal attention network," conclude the researchers.
Mark Stokes heads the Attention Group at the Oxford Centre for Human Brain Activity in the UK and was not involved in the study. He told the Guardian the study was "particularly novel because it considers natural spontaneous eye blinks".
He describes it is a carefully prepared work, with "appropriate controls", and finds the main conclusion that blinking causes disengagement "attractive and exciting".
The study appears to supports the idea that temporarily shutting off sensory inputs helps the brain fine-tune the senses and control the flow of cognitive processes. This coincides with work by other researchers, such as that of cognitive neuroscientist Daniel Smilek, of the University of Waterloo in Canada, who suggests eyeblinking is a sign of mind-wandering, and we close our eyelids so less information comes into the brain.
Written by Catharine Paddock PhD