Temporal Cortex Electrical Stimulation Enhances Verbal Memory

Low-intensity electrical brain stimulation in the lateral temporal cortex can improve verbal short-term memory, Mayo Clinic researchers report.

Patients recalled more words from a previously viewed list when low-amplitude electrical stimulation was delivered to the brain. One patient reported that it was easier to picture the words in his mind for remembering.

“The most exciting finding of this research is that our memory for language information can be improved by directly stimulating this underexplored brain area,”

said co-first author Michal Kucewicz, Ph.D., a Mayo Clinic researcher in the Department of Neurology, who compared the stimulation to “tickling” the brain.

Electrical Brain Stimulation

Memory impairments are a prevalent, costly problem in many brain diseases. Medication and behavioral therapies have limited effectiveness in many cases.

“While electrical stimulation of the brain is emerging as potential therapy for a wide range of neurological and psychiatric diseases, little is known about its effect on memory,”

said senior author Gregory Worrell, M.D., Ph.D., a Mayo Clinic neurologist.

“The next step for this project is to determine how to best apply electrical current in terms of the exact location within this area of the brain, timing and parameters of stimulation,”

said Brent Berry, M.D., Ph.D., a Mayo Clinic researcher in the Department of Physiology and Biomedical Engineering and co-first author.

Drs. Kucewicz and Berry, and colleagues focused their study on four areas of the brain known to support memory for facts and events that can be consciously recalled – the hippocampus, parahippocampal neocortex, prefrontal cortex and temporal cortex.

Enhanced Memory Function

The memory testing was done with patients undergoing evaluation for surgery to address seizures. These patients agreed to have their memory investigated using the electrodes implanted in their brains for surgical evaluation.

It is common for people with epilepsy to have memory problems because the brain circuits that underlie memory function often are affected by epilepsy. In the study, patients were instructed to read a list of words — one at a time — from a computer screen.

Electrical stimulation was applied some of this time. Patients then attempted to freely recall the words in any order.

Among 22 patients, the researchers found enhanced memory performance in the four patients with stimulation of the lateral temporal cortex but not among those with the other brain regions stimulated.

“These findings may lead to new stimulation devices that treat deficits in memory and cognition,”

said Jamie Van Gompel, M.D., a Mayo Clinic neurosurgeon specializing in brain stimulation and an author in the study.

The authors note study limitations include pain and seizure medications that may affect patient performance, the hospital setting that may disrupt patients’ sleep and wake cycles, and the fact that epilepsy affects memory.

Michal T Kucewicz, Brent M Berry, Laura R Miller, Fatemeh Khadjevand, Youssef Ezzyat, Joel M Stein, Vaclav Kremen, Benjamin H Brinkmann, Paul Wanda, Michael R Sperling, Richard Gorniak, Kathryn A Davis, Barbara C Jobst, Robert E Gross, Bradley Lega, Jamie Van Gompel, S Matt Stead, Daniel S Rizzuto, Michael J Kahana, Gregory A Worrell
Evidence for verbal memory enhancement with electrical brain stimulation in the lateral temporal cortex
Brain, awx373, https://doi.org/10.1093/brain/awx373

Image: Wellcome Images