Vagus nerve stimulation aids in memory retention

Reuters News

Researchers say that the vagus nerve may be the means by which hormonal signals that occur during important, memorable events travel to the brain, where the signals help create memories.

"[V]agus nerve activation modulates memory formation," researchers from Southern Illinois University in Carbondale, Illinois, report. Their findings are published in the January 1999 issue of the journal Nature Neuroscience.

The vagus nerve sends viscerosensory information from the heart, lungs and abdominal organs back to the brain. Studies in rodents have suggested that hormonal responses to stressful events are transmitted back to the animals' brain via the vagus nerve.

To test whether or not this pathway might exist in humans, the Illinois team studied the memory retention of subjects implanted with tiny electronic vagus nerve stimulation devices. These implants are currently being tested for possible use in preventing epileptic seizures.

Dr. Robert A. Jensen and associates had each of the subjects read a series of paragraphs. As each participant perused the text, vagus nerves were stimulated (via remote-control) at specific points. After the exercise, participants were asked to recall various words encountered during the test.

The researchers report that "...subjects had better memory retention for highlighted words in paragraphs followed by vagal stimulation than in (nonstimulated) paragraphs."

Dr. Jensen's team points out that the observed memory enhancement did not significantly improve or decline with time, suggesting that even one-time stimulation of the vagus nerve was sufficient to implant a section of text into long-term memory.

Overall, the findings suggest that event-specific hormonal activity stimulates receptors found on the vagus nerve. These signals are then "...carried by the vagus nerve to the brain," the authors say, where they trigger the formation of memory.

The investigators believe that their findings could have therapeutic implications. At some point in the future, they speculate, vagal nerve stimulation therapies might be used to "...enhance memory performance...[in] individuals experiencing cognitive impairments that result from traumatic injury or disease."

Nat Neurosci 1999;2:94-98.