Like a jazz combo, the human brain improvises while its rhythm section keeps up a steady beat. But when it comes to taking on intellectually challenging tasks, groups of neurons tune in to one another for a fraction of a second and harmonize, then go back to improvising, according to new research led by UC Berkeley.

These findings, reported Monday (July 27) in the journal Nature Neuroscience, could pave the way for more targeted treatments for people with brain disorders marked by fast, slow, or chaotic brain waves (neural oscillations) — such as Parkinson’s disease, schizophrenia and autism, which are characterized in part by offbeat brain rhythms.

Keeping the beat

“The human brain has 86 billion or so neurons all trying to talk to each other in this incredibly messy, noisy and electrochemical soup,” said study lead author Bradley Voytek. “Our results help explain the mechanism for how brain networks quickly come together and break apart as needed.”

Working with cognitively healthy epilepsy patients, Voytek and fellow researchers at UC Berkeley’s Helen Wills Neuroscience Institute used electrocorticography (ECoG) — which places electrodes directly on the exposed surface of the brain — to measure neural oscillations as the patients performed cognitively challenging tasks.  This showed how the rhythms control communication between brain regions.

They found that as the mental exercises became more demanding, theta waves at 4–8 Hertz (cycles per second) synchronized within the brain’s frontal lobe, enabling it to connect with brain sub-regions, such as the motor cortex.

“In these brief moments of synchronization, quick communication occurs as the neurons between brain regions lock into these frequencies, and this measure is critical in a variety of disorders,” said Voytek, an assistant professor of cognitive science at UC San Diego who conducted the study as a postdoctoral fellow in neuroscience at UC Berkeley.

There are five types of brain wave frequencies — Gamma, Beta, Alpha, Theta and Delta — and each are thought to play a different role. For example, Theta waves help coordinate neurons as we move around our environment, and thus are key to processing spatial information.

Off-tempo 

In people with autism, the connection between Alpha waves and neural activity has been found to weaken when they process emotional images, according to Voytek. And people with Parkinson’s disease show abnormally strong Beta waves in the motor cortex, locking neurons into the wrong groove and inhibiting movement. Fortunately, electrical deep brain stimulation can disrupt abnormally strong Beta waves in Parkinson’s and alleviate symptoms,

For the study, epilepsy patients viewed shapes of increasing complexity on a computer screen and were tasked with using different fingers (index or middle) to push a button depending on the shape, color or texture of the shape. The exercise started out simply with participants hitting the button with, say, an index finger each time a square flashed on the screen. But it grew progressively more difficult as the shapes became more layered with colors and textures, and their fingers had to keep up.

As the tasks became more demanding, the oscillations kept up, coordinating more parts of the frontal lobe and synchronizing the information passing between those brain regions. “The results revealed a delicate coordination in the brain’s code,” Voytek said. “Our neural orchestra may need no conductor, just brain waves sweeping through to briefly excite neurons, like millions of fans in a stadium doing ‘The Wave.’”

Scientists at Brown University, the Department of Veterans Affairs, UCSF, Johns Hopkins University, and Stanford University were also involved in the research.

UPDATE July 29, 2015: lead author’s correction to UC Berkeley press release: “pre-frontal” in illustration caption changed to “frontal” and  “connect with other brain regions” changed to “connect with brain sub-regions” (H/T to “betaelements” for those catches)

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Abstract of Oscillatory dynamics coordinating human frontal networks in support of goal maintenance

Humans have a capacity for hierarchical cognitive control—the ability to simultaneously control immediate actions while holding more abstract goals in mind. Neuropsychological and neuroimaging evidence suggests that hierarchical cognitive control emerges from a frontal architecture whereby prefrontal cortex coordinates neural activity in the motor cortices when abstract rules are needed to govern motor outcomes. We utilized the improved temporal resolution of human intracranial electrocorticography to investigate the mechanisms by which frontal cortical oscillatory networks communicate in support of hierarchical cognitive control. Responding according to progressively more abstract rules resulted in greater frontal network theta phase encoding (4–8 Hz) and increased prefrontal local neuronal population activity (high gamma amplitude, 80–150 Hz), which predicts trial-by-trial response times. Theta phase encoding coupled with high gamma amplitude during inter-regional information encoding, suggesting that inter-regional phase encoding is a mechanism for the dynamic instantiation of complex cognitive functions by frontal cortical subnetworks.