Scientists at Wake Forest Baptist Medical Center and the University of Southern
California (USC) have demonstrated the successful implementation of a
prosthetic system that uses a person’s own memory patterns to facilitate the
brain’s ability to encode and recall memory.
In the pilot study, published in Journal of Neural
Engineering, participants’ short-term memory performance showed a 35 to 37
percent improvement over baseline measurements. The research was funded by the
U.S. Defense Advanced Research Projects Agency (DARPA).
“This is the first time scientists have been able to identify a
patient’s own brain cell code or pattern for memory and, in essence, ‘write in’
that code to make existing memory work better, an important first step in
potentially restoring memory loss,” said the study’s lead author Robert
Hampson, Ph.D., professor of physiology/pharmacology and neurology at Wake
The study focused on improving episodic memory, which is the most
common type of memory loss in people with Alzheimer’s disease, stroke and head
injury. Episodic memory is information that is new and useful for a short
period of time, such as where you parked your car on any given day. Reference
memory is information that is held and used for a long time, such as what is
learned in school.
The researchers enrolled epilepsy patients at Wake Forest Baptist
who were participating in a diagnostic brain-mapping procedure that used
surgically implanted electrodes placed in various parts of the brain to
pinpoint the origin of the patients’ seizures. Using the team’s electronic
prosthetic system based on a multi-input multi-output (MIMO) nonlinear
mathematical model, the researchers influenced the firing patterns of multiple
neurons in the hippocampus, a part of the brain involved in making new memories
in eight of those patients.
First, they recorded the neural patterns or ‘codes’ while the
study participants were performing a computerized memory task. The patients
were shown a simple image, such as a color block, and after a brief delay where
the screen was blanked, were then asked to identify the initial image out of
four or five on the screen.
The USC team led by biomedical engineers Theodore Berger, Ph.D.,
and Dong Song, Ph.D., analyzed the recordings from the correct responses and
synthesized a MIMO-based code for correct memory performance. The Wake Forest
Baptist team played back that code to the patients while they performed the
image recall task. In this test, the patients’ episodic memory performance
showed a 37 percent improvement over baseline.
In a second test, participants were shown a highly distinctive
photographic image, followed by a short delay, and asked to identify the first
photo out of four or five others on the screen. The memory trials were repeated
with different images while the neural patterns were recorded during the
testing process to identify and deliver correct-answer codes.
After another longer delay, Hampson’s team showed the
participants sets of three pictures at a time with both an original and new
photos included in the sets, and asked the patients to identify the original
photos, which had been seen up to 75 minutes earlier. When stimulated with the
correct-answer codes, study participants showed a 35 percent improvement in
memory over baseline.
“We showed that we could tap into a patient’s own memory content,
reinforce it and feed it back to the patient,” Hampson said. “Even when a
person’s memory is impaired, it is possible to identify the neural firing
patterns that indicate correct memory formation and separate them from the
patterns that are incorrect. We can then feed in the correct patterns to assist
the patient’s brain in accurately forming new memories, not as a replacement
for innate memory function, but as a boost to it.
“To date we’ve been trying to determine whether we can
improve the memory skill people still have. In the future, we hope to be able
to help people hold onto specific memories, such as where they live or what
their grandkids look like, when their overall memory begins to fail.”