Courtesy of Robert Reinhart
The large red blob (left) indicates an increase in the timing, or synchronization, between brain waves measured over the medial frontal cortex and right lateral prefrontal cortex. This enhanced timing across brain regions specifically occurred at low frequencies, right after participants viewed negative feedback. This increase in synchronization corresponded with improvement in behavior related to learning and self-control
Source: Courtesy of Robert Reinhart

Two frontal lobe brain regions, the medial frontal cortex (MFC) and the lateral prefrontal cortex (lPFC), are believed to control most of our executive functions. Robert M. G. Reinhart of Boston University recently used a cutting-edge technique called "high-definition transcranial alternating current stimulation" (HD-tACS) to synchronize oscillations between these two regions in ways that improved brain processing and executive function. Conversely, desynchronizing brain wave oscillations between these two regions using HD-tACS had the opposite effect.

This potentially game-changing paper, “Disruption and Rescue of Interareal Theta Phase Coupling and Adaptive Behavior,” was published online, October 9, in the journal Proceedings of the National Academy of Sciences. 

During this study, Reinhart was able to use HD-tACS to isolate and alter the communication between the medial frontal and lateral prefrontal cortices while recording participants' electrical brain activity using electroencephalogram (EEG). To the best of my knowledge, Robert Reinhart is the first neuroscientist to use HD-tACS to test how populations of cells in these brain regions interact and whether these interactions are behaviorally useful for human learning and decision-making.

Transcranial electrical stimulation is delivered via electrodes placed directly on the scalp. The technique appears to quickly—and reversibly—increase or decrease executive function in healthy individuals. HD-tACS also appears to have the ability to alter behavior and self-control. The best news may be that Reinhart says HD-tACS is "safe, noninvasive, and doesn't hurt." Adding, "There's a slight tingling for the first 30 seconds, and then people habituate to it."

Someday, this state-of-the-art brain stimulation technique could allow neuroscientists to rescue executive functions in patients with neurological and neuropsychiatric disorders. 

As Reinhart explains in his paper: "Surprisingly, the exogenously driven impairments in performance could be instantly rescued by reversing the phase angle of alternating current. The results suggest executive functions can be rapidly up- or down-regulated by modulating theta phase coupling of distant frontal cortical areas and can contribute to the development of tools for potentially normalizing executive dysfunction in patient populations.”

How are the Medial Frontal Cortex and Lateral Prefrontal Cortices Interconnected?

Reinhart describes the medial frontal cortex as the "alarm bell of the brain." If you make a mistake or if something catches you off guard, the feeling of surprise you experience is triggered by the MFC firing a burst of neural activity. As a real-life example: If you were playing the piano and hit a bad chord, millions of neurons in the MFC would fire and help you correct your mistake by working with other brain regions. As another example, if your tennis coach were to point out mistakes you made during a match, the MFC would swing into action and help you make corrections.

In healthy people, the MFC works hand-in-hand via functional connectivity with the lateral prefrontal cortex, which is an area of the brain believed to play a significant role in guiding our decision-making and adaptive behavior based on goals, objectives, codes of conduct, etc. Recent studies have suggested that the medial frontal cortex and lateral prefrontal cortex communicate with one another via the precise timing of synchronized oscillations. Brain rhythms occurring at a relatively low "theta" frequency of about four to eight cycles per second (∼6 Hz) seem to play a noteworthy role in this dynamic. 

During a variety of experiments, Reinhart was able to optimize the synchronization of theta wave oscillations between these two regions. As mentioned earlier, this appeared to enhance their communication and interconnectivity and facilitated better performance on executive function tasks related to learning and self-control.

On the flip side, using HD-tACS to desynchronize or disrupt the timing of theta brain wave oscillations in these two brain regions impaired participants' ability to learn and control their behavior. Notably, Reinhart could quickly remedy discombobulation simply by changing the frequency of electrical stimulation."We were shocked by the results and how quickly the effects of the stimulation could be reversed," he said.

David Somers, the Department Chair of Psychological and Brain Sciences at BU, who was not directly involved with this particular study, commented on Reinhart's findings: "We're always looking for a link between brain activity and behavior—it's not enough to have just one of those things. That's part of what makes this finding so exciting. It's really easy to mess things up in the brain but much harder to actually improve function."

In the introduction to his paper, Reinhart sums up the significance of these findings:

"We show that the timing of alternating-current stimulation can couple or decouple low-frequency brain rhythms between segregated frontal cortical areas in a highly selective fashion without changing other neural frequencies, synchronization across the opposite cerebral hemisphere, or local neural activity. The up- and down-regulation of interareal neural coupling caused bidirectional changes in adaptive control and learning measured behaviorally. It was even possible to induce behavioral deficits and then immediately rescue this behavior in the same individuals in a matter of minutes. The findings suggest it is possible to intervene in the neural integration between frontal cortical structures that govern complex human behavior. The development of drug-free interventions for addressing disorders of excessive and deficient cortical connectivity is implicated."

Reinhart cautions that his findings are very preliminary and that more research is needed. That said, he notes that many psychiatric and neurological disorders—including anxiety disorders, autism spectrum disorders (ASD), schizophrenia, ADHD, Alzheimer's, Parkinson's Disease, and others—are marked by atypical brain wave oscillations.

Currently, most of these disorders are treated with drugs which act on receptors throughout the brain. "Drugs are really messy," Reinhart says. "They often affect very large regions of the brain." He is optimistic that sometime in the near future, finely-tuned HD-tACS brain stimulation techniques could be used to augment or replace some pharmaceutical treatments for neurological and neuropsychiatric disorders.

References

"Disruption and rescue of interareal theta phase coupling and adaptive behavior," by Robert M. G. Reinhart. Proceedings of the National Academy of Sciences (PNAS). Published online before print October 9, 2017. DOI: 10.1073/pnas.1710257114

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