Between 2021 and 2024, that has shifted. New imaging methods, better instrumentation for in-water measurement, and a growing community of researchers who themselves freedive have produced a wave of papers that are starting to describe what actually happens inside the brain during apnea. The picture that's emerging is more interesting — and more therapeutically suggestive — than the older "the body just slows down" framing implied.
This post synthesizes what the major recent papers say, what's consistent across studies, and where the research is now heading. It's aimed at the practicing freediver who wants to know what the science currently shows, not the casual interest reader. Some of the material is technical; it's worth slowing down for.
The state of the field as of 2024
Four research directions have been particularly active:
- Cerebrovascular reactivity in elite divers — how the brain manages its own oxygen supply during apnea, and how this capacity differs between elite and novice divers.
- Autonomic nervous system regulation — the simultaneous parasympathetic and sympathetic co-activation, and what trains this response.
- Cognitive performance during apnea — whether and how breath-hold affects decision-making, memory, and motor execution.
- EEG and brain state signatures — what brain activity patterns look like during voluntary breath-hold, and how they compare to other altered states.
None of these are fully resolved. The papers below each address a piece of the picture.
Patrician (2021): autonomic response in elite freedivers
One of the clearest contributions of the recent literature is the documentation of autonomic co-activation in elite freedivers. The Patrician (2021) work — building on earlier physiological measurements — confirmed that during a maximal breath-hold, elite freedivers exhibit:
- Heart rate drops of 30–50%, with some individuals reaching 20–24 BPM
- Simultaneous peripheral vasoconstriction sufficient to generate blood pressures that, in any other clinical context, would trigger hypertensive emergency protocols
- Sustained cerebral perfusion despite arterial hypoxia that would cause loss of consciousness in untrained subjects
- Recovery profiles that suggest sustained parasympathetic dominance lasting hours post-dive
The novel contribution wasn't the existence of these responses — they had been documented previously — but the precision of the measurements and the framing of the response as actively co-regulated rather than a sequence of separate adaptations. The dive response, in this framing, isn't a single reflex. It's a coordinated multi-system activation that elite practitioners have refined through training.
One practical implication for trained divers: the autonomic capacity you develop appears to generalize beyond freediving. Heart rate variability measures in elite freedivers tend to be elevated at rest, suggesting the practice produces vagal tone improvements that persist outside the water.
D'Antoni (2022): cerebrovascular reactivity and the trainable brain
The D'Antoni (2022) work focused on how the brain regulates its own blood flow during breath-hold. The key finding: elite freedivers show cerebrovascular reactivity increases of 107–165% during maximal apnea, compared to baseline measurements. This isn't simply that more blood reaches the brain; it's that the vascular system has adapted to be more responsive to the chemical signals (hypoxia, hypercapnia) that drive dilation.
This finding matters for two reasons.
First, it suggests the brain's vascular response to oxygen and CO2 changes is highly trainable. Untrained subjects show modest increases in cerebral blood flow during breath-hold (perhaps 30–50%); elite freedivers double or triple this response. The implication is that the brain learns to defend itself more aggressively with practice, allocating more of the body's blood supply to neural tissue when oxygen is scarce.
Second, this cerebrovascular adaptation may be a mechanism by which freediving training produces neuroplastic effects outside the water. Vascular health is increasingly recognized as a determinant of cognitive function and aging. If breath-hold training improves cerebrovascular reactivity in a way that persists between dives, the practice could have implications for cognitive resilience that go beyond the immediate dive experience.
Pique (2024): expert-novice cognitive differences
Pique (2024) addressed a long-standing question in the field: does breath-holding impair cognitive function, or do trained divers maintain performance despite the physiological challenge?
The study compared cognitive performance during apnea between trained freedivers and untrained controls. Results showed that trained freedivers maintained executive function — decision-making, attention switching, working memory — during prolonged breath-hold, while untrained subjects showed measurable performance decrements as breath-hold duration extended.
The mechanism is not fully clear. Possibilities include:
- The cerebrovascular adaptations described above defending cognitive tissue during hypoxia
- The amygdala-mediated suppression of suffocation alarms freeing cognitive resources that would otherwise be consumed by panic management
- Training-induced familiarity with the sensations of apnea reducing the cognitive load of attention to the experience itself
For the practicing freediver, the implication is encouraging: the cognitive demands of executing a safe dive — equalization timing, line tracking, surface protocols — appear to be preserved despite the physiological stress, provided training is adequate. This supports the standard AIDA safety framing that experienced divers can manage complex tasks at depth that would be unsafe for novices.
Steinberg: EEG alpha activity during apnea
Steinberg's work on the electroencephalographic signatures of breath-hold has been particularly suggestive. Comparing trained apnea divers to non-divers during voluntary breath-hold, the study found that trained divers maintained elevated alpha-band activity throughout the breath-hold, while non-divers showed disrupted alpha as breath-hold extended.
Alpha-band activity (8–13 Hz) is associated with relaxed alertness — the state characteristic of meditation, focused attention, and what flow researchers call "effortless concentration." The Steinberg finding suggests that what trained freedivers experience as the calm during a long breath-hold has a measurable neural signature that distinguishes it from the cognitive disruption non-divers exhibit under the same physiological load.
This finding overlaps with research on meditation neuroscience (Lutz et al., 2008; Davidson, 2003). Long-term meditators show elevated alpha-band activity at rest and during focused attention. The convergence between meditation and freediving in EEG signatures is one of the threads connecting the two practices at a mechanistic level — see our companion post on what Buddhist monks and freedivers have in common for more on this overlap.
Tuna: acute effects of breath-hold on autonomic function
The Tuna paper "The Effect of Acute Breath Holding" examined immediate autonomic responses to single breath-hold sessions. Findings included:
- Immediate post-dive elevation in heart rate variability measures (RMSSD, pNN50), indicating heightened parasympathetic activity in the recovery phase
- Sustained changes lasting hours after a single session, suggesting acute training effects rather than purely transient responses
- Greater effects in subjects who already had basic breath-hold familiarity, indicating the response is gated by some minimum training threshold
The takeaway: even a single well-executed breath-hold session produces measurable autonomic shifts that persist beyond the session itself. This has implications for how often freediving training is undertaken — even one or two CO2 table sessions per week may be sufficient to produce ongoing autonomic adaptation, rather than requiring daily volume.
The amygdala finding — Oswald and colleagues on non-ordinary states
Among the more philosophically interesting recent papers, the Oswald work on autonomic nervous system modulation during self-induced non-ordinary states of consciousness includes breath-hold as one of several practices examined. The finding most relevant to freediving: voluntary breath-hold appears to engage amygdala circuits in a way that suppresses, rather than amplifies, the panic response to high CO2.
This is the inverse of what naïve fear models would predict. The amygdala is traditionally framed as the brain's "fear center" — its activation drives the suffocation alarm that makes untrained breath-hold feel terrifying. But the recent work suggests trained freedivers learn to recruit amygdala circuits to inhibit brainstem respiratory drive, not amplify it. The amygdala becomes a regulator of breath rather than a source of panic.
The neurosurgical evidence is striking. Patients with bilateral amygdala damage experience excessive panic when exposed to CO2 — the opposite of what you'd expect if the amygdala were simply a panic generator. Electrical stimulation of intact amygdalae has been shown to induce 40–56 second apneas without distress, suggesting the structure has a direct inhibitory pathway to brainstem respiratory centers.
The practical implication for the freediver: the calm you've trained during long breath-holds is not the absence of fear circuitry. It's the active engagement of fear circuitry in a regulatory role. This is, in some sense, exactly the same skill that meditation traditions describe — the capacity to engage rather than suppress challenging sensations.
Where the field is heading — 2025 and beyond
Several research directions are likely to mature in the next few years.
1. Memory reconsolidation in altered states
The convergence of cold exposure, hypoxia, hypercapnia, parasympathetic dominance, and novel sensory environments creates conditions that, in principle, could enhance memory reconsolidation. No clinical trials have yet tested freediving in this application, but the mechanistic plausibility is sufficient that we should expect studies in the next 3–5 years. The veteran trauma trials using aquatic therapy (PCL-M reductions of 14.4 points in 8–10 weeks) are an early indicator of what this research direction may show.
2. Genetic determinants of dive response
Research on the Bajau sea nomads identified PDE10A and BDKRB2 gene variants that regulate spleen size and dive reflex strength. Future work is likely to identify whether similar variants predict response to freediving training in non-traditional populations, and whether genetic screening could help predict who benefits most.
3. Neuroimaging during in-water diving
Current research relies heavily on dry breath-hold or simulated diving. The technical challenges of fMRI during real diving are substantial, but emerging methods (functional near-infrared spectroscopy, portable EEG) may allow direct measurement of brain activity during actual underwater dives. This will likely refine many of the current findings.
4. Comparative practice research
The convergence between freediving and contemplative practice (meditation, certain breath disciplines) is suggestive but underexplored empirically. Direct comparative studies measuring autonomic, EEG, and neuroplastic markers across multiple practice types would clarify which mechanisms are general and which are specific to depth diving.
What the practicing freediver should take from this
For a working freediver who isn't a scientist, three implications:
First, the practice you're doing is more substantial than just sport. The physiological systems engaged by breath-hold training — vagal tone, cerebrovascular reactivity, amygdala regulation, cognitive control under stress — are systems that matter for health, aging, and stress resilience outside the water. Training freediving is, incidentally, training systems that have broader effects.
Second, the calm you've developed is a real, measurable skill. What feels like just "getting used to breath-hold" has measurable EEG and autonomic signatures that distinguish trained from untrained subjects. The calm isn't subjective placebo. It's a documented adaptation.
Third, the next plateau in your training may be cerebrovascular and autonomic, not pulmonary. The classical freediving training emphasis on lung capacity and CO2 tolerance is well-founded, but the recent research suggests that the responsiveness of your brain's blood supply to apnea conditions is also trainable — and may be a limiting factor for divers at the upper end of the recreational range.
Reading the source papers yourself
If you want to engage with this material directly, the papers are accessible through standard academic databases. ScienceDirect, PubMed Central, and Frontiers in Physiology are the most useful starting points for freediving-specific work. The AIDA International Medical & Science Committee also maintains a research network worth knowing about.
The Pelizzari books (Manual of Freediving, 2004; Specific Training for Freediving, 2019) remain the standard practitioner references, though they predate much of the recent neuroscience. For an integration of recent research with practical application, the white paper Neurophysiological Mechanisms of Depth, Breath, and Memory is one of the more accessible syntheses, though it remains a working document rather than peer-reviewed publication.
Sources and references
- Patrician, A., et al. (2021). Cardiovascular and autonomic response in elite breath-hold divers.
- D'Antoni, et al. (2022). Cerebrovascular reactivity adaptations in trained freedivers.
- Pique, et al. (2024). Cognitive performance during apnea: expert-novice comparison.
- Steinberg, F., et al. "Electroencephalographic alpha activity modulations induced by breath-holding in apnoea divers and non-divers." ScienceDirect.
- Tuna, K. "The Effect of Acute Breath Holding." Research on autonomic response during single breath-hold sessions.
- Oswald, et al. "Autonomic nervous system modulation during self-induced non-ordinary states of consciousness."
- Lutz, A., et al. (2008). "Attention regulation and monitoring in meditation." Trends in Cognitive Sciences.
- Davidson, R. J. (2003). "Affective neuroscience and psychophysiology: Toward a synthesis." Psychophysiology.
- Royal Society Open Science — research on extreme freediving depth and cerebral oxygen levels.
- University of St Andrews — 107m freediving brain oxygen measurements.
- Neurophysiological Mechanisms of Depth, Breath, and Memory — synthesis white paper.
- Pelizzari, U. Specific Training for Freediving: Deep, Static and Dynamic Apnea. 2019.
- LJFC: The Deep Dive Paradox — companion synthesis on therapeutic applications.
- LJFC: What Buddhist Monks and Freedivers Have in Common — the meditation parallels.
- LJFC: The Mammalian Dive Reflex Explained — foundational mechanism.
- LJFC: What Happens to Your Body During a Freedive — physiology primer.
