Brain 'shifts gears' twice in a lifetime, at ages 24 and 60, study reveals

The human brain undergoes significant organizational shifts twice in a lifetime, first around age 24 and again at age 60, according to a large-scale study analyzing over 1.3 million brain cells. Scientists mapped the prefrontal cortex, a region crucial for decision-making and memory formation, across donors ranging from infancy to 97 years old.

The research, part of the ambitious PsychAD project to create a detailed map of the human brain, identified three distinct periods of brain activity. The first, from infancy to age 24, is characterized by rapid cellular remodeling and the formation of new neural connections. Around age 24, an "unexpected inflection point" occurs, leading to a period of relative stability that persists until approximately age 60.

This stability, observed from age 24 to 60, means the brain's structure remains largely unchanged, and cellular activity settles into a predictable 24-hour rhythm. In young and middle-aged adults, neurons involved in planning and memory exhibit coordinated rhythms governed by circadian clock genes. However, this pattern begins to break down after age 60.

Following age 60, the brain enters a third phase marked by molecular changes as the effects of aging become more apparent. During this period, cells responsible for maintaining and protecting the brain become more active. Specifically, the brain's immune cells and those that insulate nerve fibers show increased activity in the evenings, focusing on repairing damaged proteins and mitigating cellular stress and inflammation. The study found that neuronal rhythms largely disappear after 60, while immune cells acquire new rhythmic activity associated with these age-related processes.

Researchers utilized RNA sequencing to examine gene activity within different brain cell types, providing insight into cellular functions at various life stages. This molecular-level analysis allowed scientists to observe changes that may not be apparent in structural brain scans alone. Previous studies, including one from the University of Cambridge, have indicated structural stabilization by age 32, but the current research delves deeper into functional and molecular alterations.

The findings from the PsychAD project are also contributing to a broader understanding of neurological diseases. Combined data from millions of cells are being used to map the progression of conditions such as Alzheimer's, Parkinson's, and various forms of dementia. One related study is exploring why some individuals with Alzheimer's maintain cognitive function despite significant brain pathology, suggesting that differences in nerve cell and protective cell function under stress could play a role in resilience.

According to Dr. Kiran Girdhar, a co-author from the Icahn School of Medicine at Mount Sinai, the generated brain atlas serves as a critical reference for understanding healthy brain aging at the molecular level. Professor Panos Roussos, lead author and also from Mount Sinai, stated that mapping cellular programs across different brain disorders provides a framework for developing precision approaches in target discovery and therapeutic development.