Where does normal brain aging end and Alzheimer’s disease take over? Will all of us eventually get Alzheimer’s if we live long enough? Despite dramatic advances in the last few years in understanding brain changes involved in Alzheimer’s, important aspects of the disease’s true nature are still very shadowy.
Most experts, however, believe Alzheimer’s is a distinct progressive pathological disease, related to aging, but not the end-stage of normal aging. In short, its not an inevitable consequence of aging. “Clearly people who live to a hundred and a hundred and ten years of age show no evidence of Alzheimer’s when we look at their brains,” says Dr. Mark Mattson, a leading researcher at the University of Kentucky. Not everybody will develop Alzheimer’s.”
According to Dr. Mattson, an aging brain and an Alzheimer’s brain have similarities. Indeed, aging is the number one risk factor for Alzheimer’s; both aged brains and Alzheimer’s brains show signs of free radical damage.
But an Alzheimer’s brain has distinct patterns of neuronal destruction, not seen in ordinary nondiseased brains Paul D. Coleman at the University of Rochester describes the diseased nerve cells from Alzheimer’s patients as filled with “black neurofibrillary tangles,” material that accumulates in the cell and is “basically choking it to death.”
Harvard’s Dr. Albert notes that Alzheimer’s begins in the area of the hippocampus and spreads to other areas of the brain, killing brain cells as it goes and leaving its victim increasingly incapacitated.
Thus, Alzheimer’s is far beyond normal aging. Something else happens to trigger the disease. Provocateurs—possibly “genetic alterations,” immune dysfunction, metabolic defects, environmental toxins, or other factors— are required to induce the distinctive brain configurations and the steep progressive decline in mental functioning typical of Alzheimer’s. Millions of dollars are going into research to identify—and eventually control—the mysterious factors that initiate a brain to Alzheimer’s.
About 4 percent of the population between ages sixty-five and seventy-four develop Alzheimer’s. The figure jumps to about 50 percent after age eighty-five.
Unquestionably, Alzheimer’s brains are different, showing massive loss of cells. Harvard neuroscientist B.T. Hyman and colleagues have measured the number of neurons in the brains of individuals who showed absolutely no signs of intellectual decline at the time of death, and in mentally impaired individuals diagnosed with Alzheimer’s disease.
The neurons were in the regions of the brain related to memory function and higher-order information processing. The astonishing finding: In the age range from sixty to one hundred, there was no apparent neuronal loss due to normal aging:” those who were intellectually intact did not show any significant decline in the number of neurons. In contrast, those with Alzheimer’s disease had drastic losses of neurons: from a 20 percent decline in those mildly impaired to 70 percent in those severely impaired.