Predicting When Dementia Starts
Murman (2015) reviews cognitive changes associated with normal aging. He states that “there is emerging evidence that healthy lifestyles may decrease the rate of cognitive decline….” Murman notes that in 1910 the average lifespan for a male was 48 years and for female it was 52. In 2010, the lifespan averages are 76 years for men and 81 years for women. Murman divides cognitive ability into multiple domains—attention, memory, executive cognitive function, language and visuo-spatial ability. Each domain “has measureable declines with age…” and of note, “speech comprehension in the setting of background noise and ambiguous speech content declines with age….”
With regard to age-related changes in brain structure and function, he reports that gray matter loss is most prominent in the pre-frontal cortex and the temporal lobes also show moderate declines in gray matter with aging. Of significance, he notes that neuronal synapses can now be measured quite accurately through immunohistochemistry. It has been suggested that when there is a loss of 40 percent or more of cortical synapses, symptomatic dementia may occur.
Murman reports that “Terry and Katzman predicted that dementia due to aging (senility) would occur at approximately age 130 without requiring the development of a disease state such as Alzheimer’s Disease (AD)…” and AD would be expected to accelerate the rate of synaptic loss. Murman states that when “synaptic density declines to 60 percent of maximal density symptoms of dementia would be expected…” and “someone with normal (cognitive) reserve and normal rate of synaptic loss with age (i.e., normal aging) would cross the dementia threshold line around age 130….” However, if one starts with lesser synaptic density, say perhaps 30 percent less than normal at age 25 years, that individual would potentially reach the dementia threshold by age 62 years.
For More Information, References, and Recommendations
Beck DL (2015) The State of the Art: Hearing Impairment, Cognitive Decline, and Amplification. Hearing Review.
Beck DL, Clark JL. (2009) Audition Matters More as Cognition Declines, and Cognition Matters More as Audition Declines. www.audiology.org (March).
Murman DL. (2015) The Impact of Age on Cognition. Seminars in Hearing 36(3).