The graph of doom: Rethinking the downward slope of cognition with ageing

Back in my early 20s, I confidently studied neuropsychology and learned that “fluid” skills like processing speed peak in our twenties, while “crystallized” abilities such as vocabulary improve into our sixties. At the time, this trajectory seemed logical—and not particularly concerning. As neuropsychologists, we were trained to compare adults to their age-matched norms when assessing the impact of brain injuries or diseases.

Now, preparing a seminar on this topic for junior psychologists, I find myself reflecting on my own experience. At nearly fifty, balancing multiple roles — several jobs, a business, teenage children, and a long-term partnership — I’m beginning to question the so-called “graph of doom.” While my processing speed may have slowed a little, my ability to juggle complex relationships and the cognitive demands of work has expanded in ways that no graph could have predicted.

Recent research supports this intuition. Large-scale studies using web-based testing reveal a far more nuanced picture, with different skills peaking at different ages. Some aspects of cognition, such as processing speed and working memory, reach their height in the twenties; others, like attention and short-term memory, peak in the thirties; and long-term memory and general knowledge often continue improving into midlife. Emotional regulation, wisdom, and social cognition appear to keep developing well into our sixties and beyond.

In other words, the ageing brain is not simply in decline — it’s adapting, reorganising, and trading raw speed for depth and perspective. Perhaps that’s why, at fifty, I feel I’m managing more — and understanding more — than I ever did at twenty.

For those interested in the research, Scientific American recently summarised this emerging evidence in Many Older People Maintain and Even Gain Cognitive Skills.

As science continues to evolve, so too does our understanding of the ageing brain — a reminder that ageing is as much about growth as it is about change.