Stimulating the brain rhythmically with electrical currents could boost cognitive function, according to an analysis of more than 100 studies

Figuring out how to improve one’s mental abilities has been of great interest to psychology and neuroscience researchers like myself for decades. From improving attention in high-stakes environments, such as air traffic management, to reviving memory in people with dementia, the ability to improve cognitive function could have far-reaching implications. New research suggests that brain stimulation could help achieve the goal of boosting mental function.

In the Reinhart Lab at Boston University, my colleagues and I investigated the effects of an emerging brain stimulation technology – transcranial alternating current stimulation, or tACS – on various mental functions in patients and healthy people.

During this procedure, people wear an elastic hood that has electrodes embedded in it that deliver weak electrical currents that oscillate at specific frequencies to their scalp. By applying these controlled currents to specific brain regions, it is possible to alter brain activity by causing neurons to fire rhythmically.

Why would rhythmically firing neurons be useful? Research suggests that brain cells communicate effectively when they coordinate the rhythm of their firing. Crucially, these rhythmic patterns of brain activity show marked abnormalities during neuropsychiatric illness. The goal of tACS is to externally induce rhythmic brain activity that promotes healthy mental function, especially when the brain cannot produce these rhythms itself.

However, TACS is a relatively new technology and its operation is still unclear. Whether it can amplify or revive brain rhythms to alter mental function has been a subject of much debate in the field of brain stimulation. While some studies find evidence of changes in brain activity and mental function with tACS, others suggest that the currents typically used in humans are too weak to have a direct effect.

When faced with conflicting data in the scientific literature, it can be helpful to conduct a type of study called a meta-analysis that quantifies how consistent the evidence is across studies. A previous meta-analysis conducted in 2016 found promising evidence for the use of tACS in altering mental function. However, the number of investigations has more than doubled since then. The design of tACS technologies has also become increasingly sophisticated.

We set out to conduct a new meta-analysis of studies using tACS to alter mental function. To our knowledge, this work is the largest and most comprehensive meta-analysis to date on this topic, comprising more than 100 published studies involving a total of more than 2,800 human participants.

After collecting over 300 measures of mental function across all studies, we saw consistent and immediate improvement in mental function with tACS. When we examined specific cognitive functions, such as memory and attention, we found that tACS yielded the strongest improvements in executive function, or the ability to adapt to new, surprising, or contradictory information.

We also saw improvements in the ability to pay attention and remember information for both short and long periods of time. Together, these results suggest that tACS in particular could improve specific types of mental function, at least in the short term.

To investigate the effectiveness of tACS for those particularly vulnerable to changes in mental function, we reviewed data from studies involving older adults and those with neuropsychiatric disorders. In both populations, we found reliable evidence for improvements in cognitive function with tACS.

Interestingly, we also found that a specialized type of tACS that can target two brain regions at once and manipulate the way they communicate with each other can both improve and impair cognitive function. This bidirectional effect on mental function could be especially useful in the clinic. For example, some psychiatric conditions, such as depression, may involve a decreased ability to process rewards, while others, such as bipolar disorder, may involve a highly active reward processing system. If tACS can alter mental function in both directions, researchers may be able to develop flexible and targeted designs that address specific clinical needs.

Developments in tACS bring researchers closer to safely improving mental function in a non-invasive, drug-free way. Current statistical evidence in the literature suggests that tACS holds promise, and an improvement in its design could help drive stronger, long-lasting changes in mental function.The conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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