Cortical Myelin Halves Brain Signaling Energy
BGU researchers found cortical myelin halves the energy cost of nerve signals without increasing their speed.
A new study from Ben-Gurion University of the Negev (BGU) reveals that the brain’s cortical gray matter cuts the energy cost of sending nerve signals in half, even though it does not increase signal speed. The study, published in PNAS (Proceedings of the National Academy of Sciences), challenges the traditional view that myelin's primary job is always to accelerate electrical communications.
The research was conducted by PhD student Oron Kotler under the supervision of Prof. Ilya Fleidervish from the Lab of Neurophysiology in BGU’s Department of Physiology and Cell Biology, in collaboration with researchers from Soroka University Medical Center, the Weizmann Institute of Science, and New York Medical College.
The Speed vs. Energy Paradox in Brain Wiring
In the peripheral nervous system, myelin acts like heavy electrical insulation wrapped around nerve fibers to speed up signal transmission up to a hundredfold while dramatically reducing energy usage. However, inside the brain's gray matter, where delicate, thin nerve fibers (axons) form dense local circuits, the exact role of myelin has remained difficult to measure.
Using advanced optical imaging, electrical recording techniques, and biophysical computational modeling, the research team examined thin axons in the cortex to compare unmyelinated and myelinated fibers:
- Unchanged Conduction Speed: Electrical signals traveled at virtually identical speeds—around 0.32 meters per second—in both unmyelinated and myelinated cortical axons.
- Halved Energy Expenditure: Myelination reduced sodium ion entry during electrical spikes by 50%. Because nerve cells must burn cellular energy (ATP) to pump out sodium and restore chemical balance, this reduction cuts the metabolic cost of signal propagation in half.
Balancing Efficiency and Cell Health
To understand why cortical myelin cuts energy costs without boosting speed, the team modeled the electrical pathways under the myelin sheath. In peripheral nerves, tight seals around long insulated stretches maximize speed. In contrast, gray matter axons feature short insulated segments and relatively "leaky" junctions.
The researchers found that this design represents an evolutionary compromise. If gray matter myelin were completely sealed to maximize speed, the space underneath would become trapped without necessary potassium ions, disrupting the cell's ability to reset its electrical charge and maintain healthy chemical balance.
Instead, gray matter myelin acts as a selective filter:
- High-Frequency Signals: Fast electrical currents that trigger nerve spikes pass directly through the myelin sheath, preserving energy.
- Low-Frequency Signals: Slower resetting currents leak through the junctions, ensuring the axon can safely clear sodium and maintain long-term stability.
Rethinking Brain Energy Budgets and Disease
The brain is one of the body's most energy-intensive organs, consuming a significant portion of daily metabolic calories. By showing that gray matter myelin prioritizes energy conservation and circuit reliability over raw transmission speed, the study offers fundamental insights into how the brain manages its energetic budget.
Understanding that cortical myelin functions primarily as an energy saver rather than a speed booster provides a new lens for researching neurodegenerative conditions and Multiple Sclerosis (MS), where damage to these delicate sheaths leaves neurons vulnerable to metabolic exhaustion and progressive loss of function.
The collaborative research was co-authored by Oron Kotler, Yana Khrapunsky, Dr. Israel Melamed, Prof. Elior Peles, and Prof. William N. Ross.
This work was supported by the United States-Israel Binational Science Foundation (BSF) (Grant No. 2017163) and the Israel Science Foundation (ISF) (Grant No. 1384/19 and 822/25).
