What is it about?

Using a combination of optical recordings, electrical measurements in mice, and computer models, we examined thin cortical axons to uncover the purpose of myelin in the brain's gray matter. We found: (1) Energy Savings: Myelination cuts the metabolic cost of sending electrical signals in half, (2) Speed Isn't Everything: The myelin offers virtually no gain in conduction velocity for these thin axons, (3) An Evolutionary Trade-off: While the sheath could theoretically be designed for faster speeds, doing so would disrupt repolarization and starve underlying ion pumps, (4) Frequency Sorting: High-frequency electrical currents (needed to trigger the signal) pass through the myelin sheath to jump forward, while low-frequency currents leak out through specialized junction zones (paranodes) to maintain healthy ion levels beneath the sheath.

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Why is it important?

This study shifts our fundamental understanding of central nervous system myelination. In the cerebral cortex, myelin evolved not as a speed booster, but as an energy-saving adaptation optimized for metabolic efficiency and long-term electrical stability. Understanding how sub-micron myelin sheaths preserve axonal energy and ion balance provides valuable insights into neurodegenerative diseases, such as Multiple Sclerosis, in which demyelination leads to axon fatigue and metabolic failure.

Perspectives

Revisiting Multiple Sclerosis (MS): Historically, demyelinating diseases like MS were viewed primarily through the lens of conduction delay or block. If myelin’s main job in thin cortical axons is energy preservation rather than speed, the primary driver of axon degeneration in cortical MS may actually be metabolic failure. Biophysical Perspective: It would be interesting to further explore the periaxonal nanodomains as frequency filters. Would molecular reengineering of these domains have a predicted effect on conduction speed, energy cost, and ion homeostasis?

Ilya Fleidervish
Ben-Gurion University of the Negev

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This page is a summary of: Cortical gray matter myelin cuts energy cost of spike propagation without increasing conduction velocity, Proceedings of the National Academy of Sciences, July 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2536534123.
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