Memory Loss In Old Age No Longer Linked To Dying Brain Cells

November 25, 1998

You must remember this: The specter of dying brain cells and an irretrievable loss of memory during old age no longer amounts to anything more than folklore.

File it away with all of the other old wives' tales.

Michela Gallagher, a professor of psychology at The Johns Hopkins University, announced recently at the 28th annual meeting of the Society of Neuroscience that there is now overwhelming evidence showing that cognitive decline in old age is far less a factor of neuro-degeneration than commonly thought.

"It's good news," Gallagher said, particularly for Baby Boomers who no longer need fear that expiring brain cells are the natural accomplice of doddering old age, subverting memory and other higher order mental processes.

By studying human data and tracing the neurological pathways of more than 800 healthy rats across their lifetimes, Gallagher has spent much of the past decade illuminating the mysterious processes that link memory and aging.

What she has discovered is that the dreaded loss of gray matter, which so many people believe is a natural result of growing old, actually is a process that occurs throughout a person's lifetime. Neuron numbers make a slow decline across decades, as cells die off regularly and consistently from youth to old age. While the brain demonstrates a remarkable ability to compensate for those losses -- forestalling any noticeable effect until the losses become, she said, "very, very profound" -- it now appears that even those neuron losses that do occur are confined to populations of cells that may not play any significant role in memory.

"It represents a real paradigm shift in neuroscience," Gallagher said. "For years, people have been trying to discover what caused the death of brain cells during aging. Our research has quite reversed that idea. We now know it's more important to understand the existing cells than to account for the ones people thought were missing. This idea of rapidly losing neurons in old age just doesn't hold water anymore."

The research, led by Gallagher, has been unusual in its collaborative nature, as she has worked closely with scientists at the Mayo Clinic, the Mount Sinai School of Medicine and Boston University, studying the behavior of rats after methodically removing specific neurons in the brain and using neuorphysiological, anatomical, and molecular-biological methods to assess the effects on memory tasks and neural communication.

Beliefs about neuro-degeneration as a basis for memory loss in aging stem, in part, from early research about Alzheimer's disease, in which neuron degeneration and a profound loss of brain mass devastates memory and other cognitive functions. Because the onset of Alzheimer's occurs in mid- to late-adult life, Gallagher said, it had been assumed that faulty memory among healthy adults also resulted from the death of neurons.

Evidence now suggests that functional changes in existing neurons actually undergird the decline in memory normally associated with aging. A careful analysis of functional properties in aged brains may hold the key to understanding memory loss in old age, she said.
Michela Gallagher home page

Johns Hopkins University

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