Track brain growth

It has long been believed that the brain grows rapidly and that by the age of 6, its size was 95% reached. Moreover, it was shown that at age 25 a slow loss of nerve cells began which would continue for the rest of life. This is not wrong, but this view does not take into account the complexity of the many structures of the brain. Their evolution over time is variable in geometry.

This is one of the many discoveries that the team from the Brain Mapping Unit at the University of Cambridge, in Great Britain, published on April 6 in the journal Nature. These researchers have achieved a real feat: they have synthesized more than 120,000 magnetic resonance images from 100,000 humans aged 115 days to 100 years. What emerges is the first detailed portrait of brain growth. A tool that will serve both clinicians and researchers. They used a platform open to the scientific community – BrainChart – to achieve this sample large enough to be statistically significant. Their results show that the four main constituents of the brain have different stages of development.

A waltz in four beats

From conception until the age of 1 year, we see that the brain is in a frantic race to develop the thickness of its cortex, its outer layer. A justified effort, because the cortex plays a fundamental role in motor skills, the senses and the higher functions of language, memory and cognition. There is then a slow decline of about 20% in volume until the age of 100 years.

Richard Bethlehem’s team was then able to demonstrate that gray matter reaches its maximum development at the age of 6 years. This matter, gray in appearance, is concentrated on the surface of the brainstem, the cerebellum and the brain. This seat of our mental operations, which go from understanding to decision-making, sees its volume slowly decrease by some 30% until the age of 100 years.

Interestingly, and which was revealed by this study, the gray matter that is adjacent to specific regions located in the heart of the brain, namely the amygdala (important seat of emotions), the basal ganglia (involved in the automatic movements, including walking) and the limbic system (the center of emotions and motivation), sees its development continue until the age of 14.

Next comes white matter. These are the neurons that serve as connections between the different regions of the brain. They are often compared to electrical wiring, which allows information to flow quickly. White matter grows more slowly than gray matter. She reaches full maturity at the age of 30. Its decline is slow and reaches only 20% at the venerable age of 100 years.

The ventricles are the last brain structure that changes with age. These cavities contain cerebrospinal fluid, which nourishes the brain and spinal cord, but also serves as a support to maintain the shape of the organ in the skull. The ventricles only expand towards the end of life, rising sharply in size from the age of 50 onwards. There is therefore a different evolution for each region of the brain.

To better understand brain diseases

The sample was so large that the researchers were able to analyze the evolution of the brain in 165 different pathologies, from autism to schizophrenia and Alzheimer’s disease. It is therefore now possible to see the impact of these diseases on the normal development of the four regions of the brain.

According to their results, the greatest deviations from the normal curves of evolution are observed with Alzheimer’s disease, mild cognitive disorders – ie the intermediate stage of dementia – and schizophrenia. In the case of Alzheimer’s, their data confirms that gray matter degeneration in patients occurs rapidly.

Towards a valid clinical tool

The ultimate goal of this approach is to have a tool that allows clinicians to compare a patient’s brain to a strong and credible statistical average of what a normal brain or brain with this pathology looks like at the patient’s exact age. . Aware that their results do not yet have this force, the researchers rely heavily on the opening of the BrainChart platform to all of their colleagues to achieve this.

They also know that there is a bias in their sampling. The majority of participants come from large cities in Europe and America and have a high enough standard of living to have access to magnetic resonance. Clinically, questions remain about important things like weight, height, and body mass index, which can vary a lot in children and affect brain growth once they become adults, which taints the value of the current samples in this study.

But this publication offers tangible hope of better understanding the evolution of diseases and making an even more accurate medical diagnosis of the various pathologies of the brain. And, fundamentally, to better understand that our brain is not a monolithically growing organ, but the fruit of an evolution full of nuances, which makes us such complex beings…