Understanding how to improve a person’s mental abilities has been of considerable interest to psychology and neuroscience researchers like me for decades. From improving attention in high-stakes environments, like air traffic management, to reviving memory in people with dementia, the ability to improve cognitive function can have consequences. considerable. New research suggests that brain stimulation may help achieve the goal of boosting mental function.
At Boston University’s Reinhart Lab, my colleagues and I examined the effects of an emerging brain stimulation technology – transcranial alternating current stimulation, or tACS – on different mental functions in patients and healthy people. .
During this procedure, people wear an elastic cap embedded with electrodes that deliver weak electrical currents oscillating at specific frequencies to their scalp. By applying these controlled currents to specific brain regions, brain activity can be altered by causing neurons to fire rhythmically.
Why would rhythmically fired neurons be beneficial? Research suggests that brain cells communicate effectively when they coordinate the timing of their firing. Critically, these rhythmic patterns of brain activity show marked abnormalities during neuropsychiatric illnesses. The goal of tACS is to externally induce rhythmic brain activity that supports healthy mental function, particularly when the brain may not be able to produce these rhythms on its own.
However, tACS is a relatively new technology and it is not yet clear how it works. The possibility of enhancing or reviving brain rhythms to alter mental function has been the subject of considerable 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 people may be too weak to have a direct effect.
When faced with conflicting data in the scientific literature, it may be helpful to conduct a type of study called a meta-analysis that quantifies the consistency of evidence across multiple studies. A previous meta-analysis conducted in 2016 found promising evidence for the use of tACS to alter mental function. However, the number of studies has more than doubled since then. The design of tACS technologies has also become increasingly sophisticated.
We set out to perform 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, consisting of over 100 published studies with a combined total of over 2,800 human participants.
After compiling over 300 measures of mental function across all studies, we observed consistent and immediate improvement in mental function with tACS. When we looked at specific cognitive functions, such as memory and attention, we observed that tACS produced the greatest improvements in executive function or adaptability in the face of new, surprising, or contradictory information. .
We also observed improvements in the ability to pay attention and to memorize information in the short and long term. Together, these results suggest that tACS may particularly improve certain types of mental functions, at least in the short term.
To examine the effectiveness of tACS for people particularly vulnerable to changes in mental function, we reviewed data from studies that included older people and people with neuropsychiatric disorders. In both populations, we observed strong evidence of improvements in cognitive function with tACS.
Interestingly, we also found that a specialized type of tACS that can target two brain regions at the same time and manipulate how they communicate with each other can both improve or reduce cognitive function. This bidirectional effect on mental function could be particularly useful clinically. For example, some psychiatric conditions like depression may involve a reduced ability to process rewards, while others like bipolar disorder may involve a highly active reward processing system. If tACS can alter mental function in both directions, researchers might be able to develop flexible, targeted designs that address specific clinical needs.
Developments in the field of tACS bring researchers closer to the possibility of safely improving mental function in a non-invasive way that does not require medication. Current statistical evidence in the literature suggests that tACS holds promise and that improving its design could help it produce stronger and lasting changes in mental function.
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