Scientists studied millions of brain cells as part of an ambitious project to map the prefrontal cortex, where decisions and memories are made.

The brain has two important “changes of gear” in adult life: one when it reaches maturity at about 24 and another when the biological effects of ageing become much more apparent at about 60, a study suggests.

The findings are part of PsychAD, an ambitious project dedicated to producing a uniquely detailed map of the prefrontal cortex, the region of the brain responsible for higher-level thinking, personality and complex behaviour, and tracking how it changes over time.
The results showed that during childhood and adolescence the proportions of different types of brain cells changed rapidly as the brain developed and its connections were reorganised.

The rate of change dropped sharply at about 24. From then until late middle age, the make-up of the brain cells was comparatively stable.
At about 60 the pattern changed again. Cells that maintain and protect the brain became much more active in dealing with inflammation and abnormal or faulty proteins.

The brain’s internal clock also appeared to change. In younger adults nerve cells involved in planning, decision-making and memory followed a clear 24-hour timetable and different biological processes became more active at predictable times of day and night. After 60, that orderly pattern started to break down.
Obituaries

Instead, some of the brain’s immune cells and the cells that insulate nerve fibres developed a new daily routine. They appeared to become more active in dealing with damaged proteins, which can contribute to disease, towards the end of the day.

The project, which was led by researchers at the Icahn School of Medicine at Mount Sinai, in New York, studied thousands of genes inside different types of brain cells.

Genes contain the instructions a cell uses to carry out its work. By analysing the RNA, a type of genetic material that is produced when different genes are active, the scientists could compare what different cells were up to in brains of different ages. The technique opened a window on how different tasks and processes became more or less important as people aged.

Across the project scientists analysed more than 6.3 million cells from nearly 1,500 donated brains. Nine studies have been published this week that draw on the data, in Nature and other journals.

One study may help to explain one of the puzzles of Alzheimer’s: why some people retain their mental abilities despite having advanced signs of the disease in their brains.

The researchers compared people who had dementia with others whose thinking remained relatively sharp, despite them having similar levels in the brain of a toxic protein known as tau, which is seen as a hallmark of the disease. Differences could be seen both in nerve cells and in astrocytes, cells that help keep nerve cells functioning and can mount protective responses when the brain is under stress.

Some forms of these astrocytes showed signs of helping nerve cells to survive damage, potentially offering clues to why certain brains are more resilient to Alzheimer’s than others.

Bron: The times.com / 23 september 2026