The beat goes in the brain

URBANA, Ill. — Like a melody that keeps playing in your head even after the music stops, researchers at the University of Illinois's Beckman Institute have shown that the beat goes on when it comes to the human visual system.

In an experiment designed to test their theory about a brain mechanism involved in visual processing, the researchers used periodic visual stimuli and electroencephalogram (EEG) recordings and found, one, that they could precisely time the brain's natural oscillations to future repetitions of the event, and, two, that the effect occurred even after the prompting stimuli was discontinued. These rhythmic oscillations lead to a heightened visual awareness of the next event, meaning controlling them could lead to better visual processing when it matters most, such as in environments like air traffic control towers.

The research was reported by Beckman and Department of Psychology faculty members Monica Fabiani, Gabriele Gratton, Diane Beck, Alejandro Lleras, first author and Beckman Fellow Kyle Mathewson, and undergraduate psychology student Christopher Prudhomme. The paper, Making Waves in the Stream of Consciousness: Entraining Oscillations in EEG Alpha and Fluctuations in Visual Awareness with Rhythmic Visual Stimulation, was published online in the Journal of Cognitive Neuroscience.

The researchers wrote that this entrainment of brain oscillators can be used to lock the timing of repetitive brain activity and, therefore, enhance, "processing of subsequently predictable stimuli."

"In nature, rhythmicity is everywhere, so it makes sense that our brain has evolved to be sensitive to rhythms in the world and to be able to latch on to them to improve neural processing," Lleras said. "It's very nice to be able to show that not only does the brain work in this oscillatory fashion but that we can harness that property that is inherent to the brain and use it to control the brain's response."

The research line goes back to a discovery by Mathewson of a pulsed inhibition mechanism in the brain that is based on oscillations in the alpha phase. This discovery supported the theory that the brain sometimes samples the visual environment in rhythmic "frames" rather than continuously, as the term "brain waves" implies.

This new work using EEG measurements demonstrated that not only do these repetitive oscillations influence what we see in the world, but those momentary snapshots are controllable.

"Simply by exposing the brain to a predictable sequence of events, people were not only more likely to detect a faint target but we could see the brain oscillations shift to line up with the rhythmic sequence and target," Beck said.

Moreover, the entrained oscillations continued even after the visual stimuli ended, and the attention of test subjects still showed greater predictive awareness of future visual events when they were in time with the previous rhythm.

"This corresponds to our theory that changes in the ability to perceive stimuli that occur rhythmically are in fact determined by the oscillations in the brain," Gratton said.