Brain waves: Why we often don’t see things

Next time you can’t find the car keys sitting right in front of you, try blaming your “travelling brain waves”.

Scientists in North America believe these neural signals exist in the visual system of the awake brain and are organised to allow the brain to perceive objects that are faint or just difficult to see – or not.

“We’ve discovered that faint objects are much more likely to be seen if visualising the object is timed with the travelling brain waves,” says John Reynolds from the Salk Institute, US, senior author of the team’s paper in Nature.

“The waves actually facilitate perceptual sensitivity, so there are moments in time when you can see things that you otherwise could not. It turns out that these travelling brain waves are an information-gathering process leading to the perception of an object.”

The waves have been studied during anaesthesia, Reynolds says, but dismissed as an artifact of it. To investigate whether they also exist in the brain when awake, he and colleagues from Salk and Canada’s Western University developed computational techniques to track neuronal activity in the visual cortex moment by moment.

They first recorded the activity of the neurons from an area of the brain that contained a complete map of the visual world then tracked the trajectories of the travelling brain waves during a visual perception task.

They held an onscreen target so observers could only detect it 50% of the time and recorded when it was spotted. Since it was not changing, they reasoned an observer’s ability to perceive it or not had to be due to some change in the neural signals inside the brain.

They found, they say, that the brain’s ability to recognise targets was directly related to when and where the travelling brain waves occurred in the visual system: when they were aligned with the stimulus, the observer could detect the target more easily.

“There is a spontaneous level of activity in the brain that appears to be regulated by these travelling waves,” says Salk’s Terrence Sejnowski. “We think the waves are the product of the activity that is propagating around the brain, driven by local neurons firing.”

The researchers next plan to examine whether the waves are coordinated across different brain regions devoted to vision. They theorise that they could serve as a gate between the sensory processing and conscious perception that emerges from the brain as a whole.