By analyzing several thousand MRIs of people affected by Alzheimer’s disease, French and Spanish researchers have observed a decrease in the volume of two key areas of the brain, the amygdala and the hippocampus. And this, years before the appearance of the first symptoms of the disease.
Affecting nearly 900,000 people in France, Alzheimer’s disease is the most common form of age-related dementia. Still incurable at present, this neurodegenerative disease slowly, progressively and irreversibly leads to the dysfunction and then the death of nerve cells in the brain.
In fact, the brain of a person affected by Alzheimer’s disease is different from that of the “healthy” brain of an elderly person, not affected by the disease. But from when can we observe a different evolution between the brain of a sick person and a brain with normal aging?
This is the whole purpose of the study conducted jointly by researchers from the CNRS, the École Pratique des Hautes Etudes (EPHE) and the University of Valencia (Spain), and published in the journal Scientific Reports.
Atrophy of the hippocampus before the age of 40
To better understand how and when a brain affected by Alzheimer’s disease evolves differently from a normally aging brain, the researchers analyzed more than 4,000 brain MRIs. 2944 MRI were those of healthy controls, aged from a few months to 94 years: their analysis enabled them to establish a “normal” model of the average cerebral evolution.
They then compared this model to an average pathological model, established from the MRIs of 1,385 people aged over 55 and affected by Alzheimer’s disease, and 1,877 young controls.
This analysis allowed them to highlight an early divergence of pathological models from the normal trajectory of aging. Indeed, two areas of the brain seem to atrophy even before the appearance of the first symptoms of the disease: the hippocampus, involved in the memory process, and the amygdala, which is the center where emotions are governed. The modification of the hippocampus is observed before the age of 40 in sick subjects, and around 40 for the amygdala.
In addition, the researchers discovered that cavities in the brain called lateral ventricles tended to enlarge earlier in people with Alzheimer’s disease, compared to healthy subjects whose brains age normally. These ventricles participate in the secretion and circulation of the cerebrospinal fluid in which the central nervous system bathes. However, the researchers acknowledge, this finding is of more limited interest than atrophy of the hippocampus and amygdala, as it has also been observed in older healthy subjects. Their enlargement would therefore be linked to the aging of the brain, and not specifically to Alzheimer’s disease.
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