Brain Stimulation for Improved Memory?

Megan Brooks

January 28, 2022

Electrical brain stimulation may have the potential to improve verbal memory, results of a small study of patients with epilepsy suggest.

Investigators observed improvements in patients implanted with a responsive neurostimulation system (RNS) to control seizures, in that the patients had improved word recall when the system was activated.

Beyond epilepsy, "we suspect that our results would be broadly applicable regardless of the underlying condition, for example, memory loss with Alzheimer's disease or traumatic brain injury," Zulfi Haneef, MBBS, MD, associate professor of neurology, Baylor College of Medicine, Houston, Texas, told Medscape Medical News.

"Mental health conditions such as depression or psychosis could also benefit from targeted electrical stimulation. While we focused on enhancing a preferred brain function [such as memory], parallel areas of research may target enhancing function, [such as weakness following stroke] or suppressing function [to manage conditions such as chronic pain,]" Haneef added.  

The study was published online January 17 in Neurosurgery.   

As reported by Medscape Medical News, the RNS system (NeuroPace Inc) is approved by the US Food and Drug Administration to treat medically refractory focal seizures in adults. Following implantation of the system, patients attend the clinic for adjustments about every 8-12 weeks.

The investigators studied 17 patients with epilepsy and RNS implants who attended the clinic for routine appointments. A clinical neuropsychologist administered the Hopkins Verbal Learning Test-Revised (HVLT-R), a well-validated list-learning measure of memory and verbal learning.

Patients were read a list of 12 semantically related words and asked to recall the list after three different learning trials. Active or sham stimulation was performed for every third word presented for immediate recall. 

The investigators found that the HVLT-R delayed recall raw score was higher for the stimulation condition compared with the nonstimulation condition (paired t-test, P = .04, effect size d = 0.627).

"The patients were not aware of when the RNS system was being activated. We alternated when patients were undergoing stimulation vs no stimulation, and still found that when patients' RNS systems were activated, their memory recall score was greater than when there was no stimulation," Haneef said in a release.

This suggests the "human memory can be potentially improved by direct electrical brain stimulation at extremely low currents," Haneef told Medscape Medical News.

Most patients in the study had stimulation of the hippocampus, the brain's memory center.

"Moving forward we would want to look at how different patterns or standardized stimulation patterns affect memory. Ultimately, the underlying brain rhythms responsible for these changes in brain function need to be understood so that a more targeted and precise application of electrical stimulation can be achieved," Haneef said.

The researchers also caution that for this preliminary study, no follow-up testing was conducted to determine whether the memory improvement was transient and settled back to baseline after a specified period.

However, they note, this study lays the groundwork for larger-scale and extensive studies examining the nuanced effects of brain stimulation on human cognition and memory.

The study was funded by the Mike Hogg Foundation. Haneef and two co-authors received coverage for travel expenses but no honorarium for a NeuroPace advisory meeting.

Neurosurgery. Published online January 17, 2022. Abstract

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