A recent study reveals that the human brain, when lacking energy, might draw from its own fatty tissues. This discovery suggests a new form of neuroplasticity, allowing the brain to function during prolonged endurance efforts.
Brain scans of marathon participants show that when cerebral glucose is dangerously low, certain neurons might start consuming myelin. This fatty sheath surrounds the brain's nerve fibers. It helps with the efficient transmission of neural messages. Myelin, far from being just a static insulator, appears to be reusable. Its structure adapts to environmental changes. It seems that some brain cells recycle myelin for energy, but only in cases of absolute necessity.
Myelin: an energy reserve?
Analysis of MRI images from ten runners—eight men and two women—before and after completing a 26-mile (42 km) marathon revealed significant changes in myelin markers present in the brain's white matter, an area particularly rich in fatty sheaths.
It was observed that twenty-four to forty-eight hours after the race, a notable loss of myelin occurred in brain regions involved in motor function, coordination, as well as sensory and emotional integration. Furthermore, myelin markers began to increase two weeks after the event and returned to their initial levels two months later in the six participants who continued to be monitored.
According to the research team led by Pedro Ramos-Cabrer and Alberto Cabrera-Zubizarreta, myelin could play a role as an energy reserve for the brain, stepping in when cerebral nutrients are lacking. They thus proposed the concept of "metabolic plasticity of myelin" to describe this phenomenon.
This hypothesis challenges the previously accepted idea that the brain avoids using fats as an energy source. Although the study was conducted on a small sample, its findings are supported by research on mice, which demonstrated that myelin could serve as a lipid reserve in cases of glucose deficiency.
Impacts and perspectives
Myelin, playing a crucial role in the nervous system's functioning, sees its significant loss associated with neurological conditions such as multiple sclerosis. It is suggested that the brain, by mobilizing myelin from specific areas, might induce temporary self-damage to preserve the organ's overall integrity.
This observation aligns with cognitive studies, which have highlighted slower reaction times and reduced memory performance in runners immediately after a marathon. It is important to note, however, that brain function shows rapid improvement during the recovery phase.
Myelin, present in greater quantities in the most recent regions of the human brain, could represent a significant evolutionary adaptation. This fatty substance might have played an important role, allowing our ancestors to cover long distances while maintaining a high level of cognitive vigilance. The results of this study, which shed light on this hypothesis, were published in the scientific journal
Nature Metabolism.
To go further: How does the brain use energy?
The brain, despite its small size, is an extremely energy-hungry organ. It consumes about 20% of the body's total energy, while representing only 2% of its mass. This considerable energy expenditure is necessary to maintain constant neuron activity and ensure nerve signal transmission.
Glucose is the brain's primary energy source. This simple sugar, transported by blood, is converted into ATP (adenosine triphosphate), the energy molecule used by brain cells. However, in cases of glucose shortage, the brain can also use ketone bodies, molecules produced by the liver from fats.
Myelin, as a lipid reserve, could play a key role in supplying energy to the brain during intense physical efforts or metabolic stress situations. This mechanism, still poorly understood, is the subject of in-depth research to better understand the complex interactions between brain metabolism and cognitive functions.
The efficiency with which the brain uses energy is essential for its proper functioning. Disruptions in energy supply can lead to neurological and cognitive disorders. It is therefore important to maintain a constant supply of glucose and essential nutrients to ensure brain health.
Article author: Cédric DEPOND