A New Memory Aid

by Guy McKhann, M.D.

May 2, 2017

This is a column from Dana's print publication, Brain in the News.

Stimulation of the brain has a long history. It has usually been used to modify abnormal symptoms. In recent times, deep brain stimulation has become widely used for Parkinson’s disease and for relief from depression that is refractory to medicine. An encouraging study by psychologists at the University of Pennsylvania may have uncovered a new benefit to brain stimulation: enhancing memory.

This is not entirely new; investigators, in the past, have stimulated an area of the brain involved with memory processing, the hippocampus. The results were mixed—sometimes memory was enhanced and at other times memory was impaired. Michael Kahana, Ph.D., and his colleagues at Penn, as well as investigative neurosurgeons at 20 other institutions, have tried to determine if stimulation could improve memory, while also asking, “Does the state of the brain make a difference?”

The researchers took advantage of the fact that patients with epilepsy may not respond to anticonvulsants. An alternative therapy is to find the place in the brain where seizures originate and surgically remove this focus of seizure activity. To do this they placed multiple electrodes in the brain, not only to determine the origin and spread of the seizure activity, but also to locate areas of the brain they did not want to damage. They included results from 150 patients in their studies. The electrodes were placed on the surface of the brain, or in the brain, to study a particular person’s epilepsy. Thus, not all electrodes were in memory-processing areas. In some patients, none were. These latter subjects provided a valuable control group for analysis of stimulation in non-memory areas.

Kahana and his colleagues found that some areas of brain were already in a high efficiency encoding state and thus ready to form memories. Stimulation to a high encoding area actually disrupts memory. On the other hand, stimulation to areas in a low encoding state improves memory.

These studies add a new dimension to the field of brain stimulation. Previously the emphasis was on the location, or site, of stimulation. While site is still important, the physiologic state at that site may determine if stimulation will have positive or negative effects. Determining the existing state prior to stimulation may require having an electrode in that area. However, advances in MRI and EEG may provide needed data.

These studies have been done in a very specialized group of subjects. It is hoped that what is learned here will have application to enhancing memory function in subjects with loss of memory, as happens in Alzheimer’s disease and other dementias.

For more information on this topic, see the New York Times article about a "brain pacemaker" and the research paper from Dr. Kahana and his colleagues.