Study uncovers insights into human memory

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Wissam Deeb, M.D.

Alzheimer’s disease is a debilitating neurodegenerative disorder affecting more than 5.5 million Americans. Now, new clinical trial results published in the New England Journal of Medicine yield a finding that could advance our understanding of human memory.

A recent trial involving 42 patients evaluated deep brain stimulation targeting the fornix, an arch-like structure connecting the hippocampus to other parts of the limbic system, with a primary aim of improving cognition in Alzheimer’s patients. Though that objective was unsuccessful, a research team led by Wissam Deeb, M.D., assistant professor of neurology at the University of Florida, analyzed a phenomenon of flashback-like cognitive experiences in nearly half of the patients occurring during initial programming of the stimulator.

“These observations build on previous work, starting with the seminal experiments done by Wilder Penfield and Phanor Perot about the brain structures and circuity involved in the process of memory formation, storage and retrieval. This report shows that stimulation in the fornix area of the brain can stimulate vivid and detailed flashbacks in patients with Alzheimer’s disease. The occurrence of these phenomena adds further support to the central role of the fornix and surrounding structures in memory,” said Deeb, lead author of a correspondence article published Aug. 21 and signed by top experts from across the U.S. and Canada.

A total of 20 patients spontaneously described in vivid detail what were believed to be past experiences, such as one man’s sense of satiety and taste of sardines eaten on his front porch long ago. In all, the 20 patients described 85 unique memory recollections. As stimulation voltage was increased, there was an increase in detail and clarity of memory.

“In a disease that affects memory profoundly, deep brain stimulation of the fornix elicited flashbacks about previous experiences, sometimes a couple of decades old. Although this treatment did not improve memory, the information gleaned will improve our understanding of memory function as well as dysfunction with the hope of better treatments for Alzheimer’s disease,” Deeb said.

“These observations provide a unique opportunity to better understand the underpinnings of human memory disorders and may help us in the formidable journey aimed at developing meaningful treatments for the millions of patients suffering from Alzheimer’s disease,” said Michael S. Okun, M.D., chair of neurology and executive director of the Norman Fixel Institute for Neurological Diseases at UF Health and senior author on the paper.

Read the paper in the New England Journal of Medicine.

Read a U.S. News & World Report article about the paper.