The neuroscience of aging

I’ll start with the bad news first. The human brain reaches it’s physical peak around the age of 25. After that it’s all downhill. The prefrontal cortex and underlying white matter is the last area of the brain to develop (including myelination); that area is also the first to start the decline. Myelination of the frontal cortex typically isn’t completed until the early to mid 20s. Its slow degradation starts quickly after it finishes development. This slow degradation of the brain correlates with slowed processing speed initially and, later in life, with declines in all areas of cognition. The good news is that cognitive performance in most areas does not typically decline until the mid 50s; many abilities such as verbal continue to increase until the mid 50s or early 60s. While there is often global brain matter loss (slowly over the decades), specific areas of the brain change at different rates (with some areas exhibiting volume increases until the mid 50s or so).

This news can be discouraging for people who are older than 25 (such as myself) – knowing that I am on the downward slope, at least as far as brain volume, myelination, and processing speed are concerned. I wrote about the bad news first so now the good news. Even though cognitive performance starts to decline, on average, in the mid 50s, many domains increase between age 25 and age 55; thus, the declines in late life often merely bring cognitive performance back down to where it was in the mid 20s. Of course processing speed in late life is a lot lower than in the early 20s but verbal memory and abilities, reasoning, and spatial abilities are quite intact in late life. Math abilities tend to decrease significantly over life though. The graph shows cognitive performance as measured by a 35-year longitudinal study (actually a sequential research design – both cross-sectional and longitudinal) (Schaie, K. W. Intellectual Development in Adulthood: The Seattle Longitudinal Study. Cambridge Univ. Press, Cambridge, 1996).Cognition across the lifespan

For a comprehensive review of cognitive and neurological changes associated with aging read Trey Hedden and John D. E. Gabrieli’s Nature Review: Neuroscience article published in February 2004. I’ve included a link to a PDF of the article: Aging article.

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