Parts of the brain are temporarily "switched off" when we blink, scientists have found. Writing in the journal Current Biology, a team from the University College London says that this is true even if light is still entering the eyes. The researchers said this could explain why people do not notice their own blinking, allowing us to have an "uninterrupted view of the world."
A blink lasts for between 100 and 150 milliseconds. We automatically blink 10 to 15 times a minute to moisten and oxygenate the cornea. During a blink, although no light enters the eyes, we do not consciously recognize that everything has momentarily gone dark.
The UCL team set out to discover why humans are not disturbed by these "mini blackouts". They used a specially-designed device that was placed in the mouths of volunteers while they were lying in a magnetic resonance imaging (MRI) scanner. MRI scanners allow brain activity to be monitored.
The device emitted a strong light that lit up the eyeballs through the roof of the mouth. Because of this, the light falling on the eye remained constant even when the participants blinked. This meant that the scientists were able to measure the effects of blinking on the participants’ brain activity independently of the amount of light hitting the eye.
In the experiment, the researchers found that blinking suppressed brain activity in certain parts of the brain, in particular the visual cortex and other areas which are usually activated when people become conscious of visual events or objects in the outside world.
Davina Bristow, who led the research, said: "We would immediately notice if the outside world suddenly went dark, especially if it was happening every few seconds. But we are rarely aware of our blinks, even though they cause a similar reduction in the amount of light entering the eye. Transiently suppressing the brain areas that are involved in visual awareness during blinks may be a neural mechanism for preventing the brain from becoming aware of the world going dark with every blink."
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