When the human brain runs low on energy, it may resort to an unexpected survival strategy—feeding on its own fatty tissue. A recent study on marathon runners suggests that during extreme endurance, the brain may break down myelin. Myelin is a fatty sheath around nerve fibers. This breakdown helps to sustain function.
This finding hints at a previously unknown form of neuroplasticity. It allows the brain to adapt to intense physical stress. The brain achieves this by temporarily sacrificing some of its protective layers.
MYELIN: MORE THAN JUST A PROTECTIVE BARRIER
Myelin acts as an insulator, helping neurons send signals efficiently. Still, new research suggests that myelin is not a static structure. Myelin can be broken down and repurposed as fuel when the brain is starved of glucose.
A team of neuroscientists from Spain, led by Pedro Ramos-Cabrer and Alberto Cabrera-Zubizarreta, conducted MRI scans on 10 marathon runners (8 men and 2 women) before and after a 42-kilometer (26.1-mile) race. Their results revealed significant reductions in myelin markers in brain regions linked to:
- Motor function and coordination
- Sensory processing
- Emotional integration
These changes suggest that neurons may temporarily break down myelin for energy when glucose is depleted.
A ‘METABOLIC SAFETY NET’ FOR THE BRAIN
The researchers have coined this phenomenon “metabolic myelin plasticity.” It is a process where the brain selectively taps into fatty deposits. This occurs when it faces an energy crisis. This mechanism may allow the brain to prioritize essential functions while preserving overall white matter integrity.
Interestingly, myelin markers in the runners’ brains began to recover within two weeks. By two months post-marathon, myelin levels had fully stabilized in the participants who continued with follow-up scans.
This suggests that while the brain may cannibalize its own tissue in the short term, it also possesses a remarkable ability to regenerate lost myelin once energy levels return to normal.
WHY THIS MATTERS: THE EVOLUTIONARY ROLE OF MYELIN
Neuroscientists once believed that the brain largely avoided burning fat for fuel, even under extreme stress. However, this study—along with previous research on mice—challenges that assumption.
The most recently evolved areas of the human brain have higher myelin concentrations. This suggests that this fatty layer may have played a key role in human evolution.
Could myelin have been our ancient survival tool? Early humans relied on endurance running to hunt prey—a technique known as persistence hunting. If myelin helped sustain brain function during long chases, it might have provided humans with a unique cognitive advantage. This edge could have set humans apart from other species.
COGNITIVE IMPACTS: WHY RUNNERS STRUGGLE TO THINK CLEARLY AFTER A RACE
The temporary loss of myelin may explain why marathon runners often experience cognitive difficulties immediately after a race. Studies have found that:
- Reaction times slow down
- Memory performance declines
- Mental fatigue increases
However, these effects reverse quickly with recovery, mirroring the rebound in myelin levels seen in brain scans.
WHAT’S NEXT? FUTURE RESEARCH ON BRAIN METABOLISM
While this study provides compelling evidence, it is still a pilot study with only 10 participants. Future research with larger sample sizes and direct biochemical analysis of myelin breakdown will be needed to confirm these findings.
Understanding how myelin functions as an energy reserve could have significant implications. These implications are relevant for neurological disorders like multiple sclerosis. In multiple sclerosis, myelin is progressively lost.
If scientists can uncover ways to enhance myelin regeneration, it could lead to breakthrough treatments. These treatments could address brain injuries and degenerative diseases.
FINAL THOUGHTS: A BRAIN BUILT FOR ENDURANCE
The idea that the brain can temporarily consume itself to keep functioning during extreme physical exertion is both fascinating and concerning. This adaptation might have helped our ancestors outlast prey. Nevertheless, it raises new questions about how modern endurance athletes should manage brain health during prolonged exercise.
Perhaps, in pushing human limits, we are only just beginning to understand the brain’s true adaptability.
