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expert reaction to a study on brain stimulation and improvement in tasks on working and long-term memory

A study published in Nature Neuroscience looks at the use of repetitive neuromodulation to improve working memory and long-term memory in older adults.


Dr Nir Grossman, UK Dementia Research Institute Group Leader at Imperial College London, said:

“The brain’s cognitive function requires rhythmic activities to coordinate the computation of distributed neural cells. 

“Grover et al. tested whether augmenting specific patterns of rhythmic brain activity previously linked to memory function could improve memory accuracy. During the study, the participants were asked to encode and recall a series of words as accurately as possible. To augment the rhythmic brain activity, during the task, the team applied weak electric fields via scalp electrodes to the dorsolateral prefrontal cortex (DLPFC) or the inferior parietal lobule (IPL) of the participants’ brain. 

“Earlier studies exploring a similar question with a similar approach led to inconclusive results. However, in contrast to most earlier studies, Grover et al. tested the stimulation effect in older rather than young adults over multiple stimulation sessions rather than a single stimulation session. The study is a natural advance of an earlier report by the team (Reinhart, Robert MG, et al. Nature neuroscience, 2019) in which a single stimulation session was tested. 

“They found that stimulation of the DLPFC with a frequency in the gamma band improved the accuracy by which the participants memorised the first few words in the series, while stimulation of the IPL at the theta band improved the accuracy by which the participants memorised the last few words. 

“These results support the notion that the brain deploys different circuits to encode and maintain a memory. The study’s outcome provides encouraging early-stage evidence of a potential interventional strategy to improve memory performance. 

“Future studies that combine neuroimaging and perhaps differential stimulation during memory encoding and recall could better pinpoint the mechanism of action, i.e., the change in brain activity that led to the behaviour benefit. In addition, the translation of the results to other memory tasks should be tested.”


Prof Masud Husain, Professor of Neurology & Cognitive Neuroscience, University of Oxford, said:

“These are very exciting results. The researchers used carefully designed transcranial alternating current stimulation, and found highly specific improvements in either short or long term memory, depending on how and where over the brain they stimulated. They replicated these findings in a completely different set of participants which is impressive.”

“We have to bear in mind though that the effects on memory were of the order of remembering three to four more words out of a list of 20, but this improvement in memory ability was detectable one month after stimulation which is quite remarkable.”

“Whether, these improvements would occur for everyday memories, rather than just for lists of words, remains to be tested.”


Prof Dorothy Bishop, Professor of Developmental Neuropsychology, University of Oxford, said:

“This is a classic case of an overhyped study. The press release implies that electrical brain stimulation can produce long-lasting improvements in working memory and long-term memory in older people, citing examples of remembering a train platform or where you parked your car after a holiday.  

“What the study actually shows is that if you give people lists of words to recall, repeating the task over several days, then recall is improved if you apply electrical stimulation to the brain while they listen to the lists, but this is not a general memory boost: the results depend on the precise nature of the brain stimulation, the location of the electrodes and whether you are looking at recall for words at the start or end of the list.  There is no indication that the beneficial effect would extend to everyday activities performed when no brain stimulation was taking place, such as those described in the press release.

“Studies of electrical brain stimulation came into vogue about 20 years ago. It’s important not to confuse the method with electroconvulsive therapy (ECT). Brain stimulation involves a very mild current applied via electrodes to the scalp, and the most that the person feels is mild tingling at the site of stimulation. The methods have evolved over the years and this study used rhythmic stimulation that is set at a frequency that is intended to influence neural oscillations.  There have been many studies of electrical stimulation on memory but, as the authors note, results have been inconsistent. The claim here is that one combination of brain region and stimulation frequency improves ability to remember words at the start of the list and another affects ability to remember words at the end. This is of interest because these so-called primacy and recency effects are thought to index different memory systems.  Given the inconsistencies of prior findings in this field, it is good to see that the main result was followed up by a further study with a new sample which obtained the same pattern of results. The value of the study is in its ability to throw light on brain mechanisms underlying memory. It’s unfortunate that it’s described as if it might help provide a general boost to memory function in older people in their everyday activities. There is no evidence that is the case.”


Dr David McGonigle, Lecturer in Neuroimaging and Neurostimulation, Cardiff University, said:

“This is an extremely promising piece of work. The technique used (transcranial electrical stimulation: tES) has much potential: it uses rubber electrodes placed on the scalp, with most studies producing only minor side effects like tingling and itching. Yet, as this study demonstrates, it can be extremely powerful if used in a manner that combines neuroscientific rigour with precise targeting of brain regions. Suppose it’s possible to extend the memory retention period beyond one month? In that case, this kind of treatment may soon be a viable, non-pharmacological means to fight memory loss in old age.”


Dr Susan Kohlhaas, Director of Research at Alzheimer’s Research UK, said:

“This is a small early stage study that showed some memory benefits for older people who received a type of non-invasive brain stimulation, involving specialised equipment and very specific procedures.

“The researchers found that stimulating certain parts of the brain for 20 minutes a day over four days led to improved memory skills up to one month after the brain stimulation. Larger and longer-term studies will be necessary to understand the impact that this type of technology could have on older people in the future and if the effect is long-term.

“It is important to note that these participants did not have memory problems, and this research doesn’t tell us anything about the potential to slow cognitive decline caused by diseases like Alzheimer’s. Many people experience changes in their memory skills as they get older and it’s not necessarily a sign of dementia. Anyone with concerns about their memory should speak to their GP.

“We don’t know if brain stimulation techniques have potential to help people with dementia but there is research underway in this area. Investment in research has started to open up new and innovative approaches to tackling the diseases that cause dementia and we must continue to explore all avenues that hold the potential to becoming life-changing treatments.”



‘Long-lasting, dissociable improvements in working memory and long-term memory in older adults with repetitive neuromodulation’ by Shrey Grover et al. was published in Nature Neuroscience at 16:00 UK time on Monday 22 August.




Declared interests

Prof Masud Husain: “No conflicts of interest.”

Prof Dorothy Bishop: “No conflicts of interest.”

Dr David McGonigle: “I’ve worked with tES for over ten years and have run >300 participants in various studies. Nothing to declare.”

For all other experts, no reply to our request for DOIs was received.


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