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A new bioRxiv preprint reports changes in brain functional connectivity after seven months of freediving training—but it does not show that freediving rebuilt the brain’s anatomy or improved memory. The study tracked 17 male recreational freedivers, and its findings are preliminary: the manuscript had not been peer reviewed as of October 2026.
What “reorganize the brain” means in this study
The headline refers to patterns of functional connectivity: how activity in different brain regions is statistically related, as measured with fMRI. It does not mean researchers observed new anatomical wiring, growth, or broad physical restructuring of the brain.
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In their bioRxiv preprint, Micaux and colleagues write that “These findings suggest that repeated voluntary hypoxia during freediving training is associated with selective functional reorganization of hippocampal and large-scale brain networks.” The authors add that “This pattern may reflect adaptive neuroplasticity linked to preserved episodic memory under intermittent hypoxic exposure.” Those are the authors’ interpretations of preliminary results, not established evidence that training caused beneficial changes. Read the preprint record.
What the seven-month study reported
The researchers assessed 17 male recreational freedivers before and after a standardized seven-month training period. They also assessed 20 matched male aerobic-trained controls at baseline. Analyses covered whole-brain region-to-region connectivity, connectivity linked to hippocampal seed regions, and associations with episodic-memory performance.
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The preprint reports that freedivers had connectivity patterns distinct from controls during both apnea and rest. After training, reported changes involved several systems:
- Salience and frontoparietal networks, involved in detecting relevant information and coordinating higher-level processing.
- Sensorimotor and visual systems.
- Cerebellar regions, which contribute to movement coordination and other functions.
For hippocampal connectivity, the authors report lower connectivity with sensorimotor and default mode regions and higher connectivity with cerebellar and visual areas. Some effects were stronger after training. Specific post-training connectivity measures were associated with episodic-memory scores, but an association does not show that connectivity changes caused better memory—or that memory improved.
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Does freediving affect memory or brain structure?
A separate peer-reviewed longitudinal study by Noulhiane and colleagues followed 17 male freedivers and 20 male non-freediver athletes across seven months. It found no significant group or training-period differences in hippocampal subfield volumes or episodic-memory performance. See the 2025 study in the Journal of Integrative Neuroscience.
That result does not contradict the preprint’s connectivity findings: the studies measured different outcomes. Functional connectivity can change without a detectable change in the size of hippocampal subfields or in a memory test score. Taken together, the studies do not establish that freediving enlarges or damages brain structures, or that it enhances memory.
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How this compares with research during apnea
Other studies have examined the brain while someone is holding their breath. They provide context for how the brain responds acutely to apnea, but they cannot confirm that months of training produce lasting connectivity changes.
| Study and design | What it measured and reported | What it can tell us |
|---|---|---|
| Annen et al., 2021: one world champion freediver during 6.5 minutes of dry static apnea | EEG showed increased alpha-band power and functional connectivity, alongside decreased delta-band connectivity. fMRI showed connectivity increases within default mode and visual areas and decreases in pre- and postcentral cortices. Study in Brain Structure and Function. | An acute response in one person, not evidence of long-term training effects. |
| Vestergaard and Larsson, 2019: 15 freedivers and 17 controls during breath-holding and a hypoxic challenge | Cerebral blood flow increased 107% in freedivers during breath-holds; the authors reported that cerebral oxygen delivery was sustained and oxygen consumption was unaffected. Study in the Journal of Cerebral Blood Flow & Metabolism. | A physiological blood-flow response during apnea, not proof of chronic brain reorganization. |
| Bailey et al., 2017: review reexamining previously published data | The review summarized cerebral blood-flow increases of 96% in freedivers and 209% in mountaineers, and cerebral oxygen-delivery increases of 24% and 183%, respectively, relative to normoxic baseline controls. Review in High Altitude Medicine & Biology. | Figures summarized from earlier data in a review, not results from a new experiment. |
What remains uncertain
The new preprint has important limitations. Its freediver sample is small and includes only men. Controls were measured at baseline but not again after seven months, so the design cannot cleanly separate training-related changes from other changes over time. The findings are based on fMRI connectivity and do not establish structural remodeling or a health benefit.
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The manuscript was not peer reviewed as of October 2026, and results or interpretations may change during review or revision. The evidence supports a cautious reading: the authors report connectivity differences associated with freediving and training, while the cause, meaning, and practical consequences remain unsettled.
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