Deep probes into the brains of Alzheimer’s patients can produce unexpected flashbacks from decades ago, giving scientists a new look at how memories work.

In a study using deep-brain electrical stimulation, one patient recalled having cocktails on a long-ago Caribbean vacation, and another remembered feeling full after eating sardines on his front porch two decades ago, according to research published in the New England Journal of Medicine.

“The stimulation has activated them, which means that the memory circuitry is still there. It’s just the brain is having difficulty retrieving it.”
Dr. Wissam Deeb
University of Florida

The findings indicate that the memories are not lost, which could have significant implications for research into Alzheimer’s disease, said Dr. Wissam Deeb, lead researcher and an assistant professor of neurology at the University of Florida.

“The stimulation has activated them, which means that the memory circuitry is still there. It’s just the brain is having difficulty retrieving it,” Deeb told Considerable.com

“This is not solving the problem of Alzheimer’s, but it is exciting to see. It gives us a certain window to see how memory works.”

Some 5.8 million Americans have Alzheimer’s, a number predicted to rise to nearly 14 million by 2050, according to the Chicago-based Alzheimer’s Association.

One in three seniors dies with Alzheimer’s or some other form of dementia, according to the association.

The flashbacks in the Alzheimer’s patients emerged as researchers were using deep brain stimulation to test cognitive functions.

Unlike surface electrical stimulation that has shown some cognitive improvements in dementia and other non-invasive stimulation that can improve working memory, deep stimulation entails boring holes into the skull and inserting  small electrodes attached to a battery.

The electrodes were aimed at the part of the brain called the fornix, an area important in memory formation.

The most intriguing flashback came from the patient who recalled drinking a margarita at a resort in Aruba.

The researchers were looking to see if deep stimulation improved cognitive functions in Alzheimer’s patients over time, but results showed no significant changes in their thinking, reasoning or memory abilities.

But nearly half of the 42 patients in the study reported vivid flashbacks, some spanning back two or three decades, Deeb said.

The most intriguing flashback came from the patient who recalled drinking a margarita at a resort in Aruba and could still feel being inebriated and feel the sensation of the limes, he said.

“For me, that was very exciting, how detailed that memory was,” he said. “That a person can remember feeling drunk, that was exciting to see.”

Another patient’s recollection of helping look for some lost object grew clearer as the electrode voltage was increased, he said. With stronger stimulation, the patient remembered his son was present and that the incident occurred at night around Halloween.

The stirred-up memories were not particularly important or emotional, and they were not recollections that the patients had frequently referred to, according to their caretakers, Deeb said.

A follow-up-study is underway to look at such recollections more systematically, as they were unexpected in the initial study, he said.

“It was surprising,” he said.

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