Forgetting where one has parked the vehicle or why one went into a room is frequently waved off as an inevitable process of aging.

A revolutionary study has now shown, however, that brain aging does not proceed as the gradual, steady process we thought. Rather, it fluctuates suddenly and profoundly, with one of the most significant changes taking place at the age of 43.

Researchers at the Stony Brook University examined close to 20,000 brain scans from large databases such as the UK Biobank and the Human Connectome Project by applying functional MRI. What they concluded defied previous assumptions regarding aging.

Rather than a linear S-shaped decline, brain network stability moved along an S-shaped line. It was stable until age 43, then entered a steep destabilization process, with a peak at age 66, before finally entering a plateau.

This middle-aged age range—from 40 to 60—appeared as a highly vulnerable stage for brain health. Yet specialists are convinced this is also a critical window for intervention.

"Knowing precisely when and how brain aging speeds up provides us with strategic time points for intervention," said Mujica-Parodi, director of the Laboratory for Computational Neurodiagnostics at Stony Brook University.

The research also investigated why the brain begins destabilizing at midlife, and metabolism was found to be a primary factor. The scientists zeroed in on glucose, the brain's major energy source, that relies on insulin and GLUT4 transporters to process efficiently.

With age, the sensitivity to insulin decreases, and it becomes more difficult for neurons to use energy. The research established that increasing blood sugar indicators such as HbA1c correlated with the onset of brain network destabilization.