One of the oldest arguments in hyperbaric medicine is about pressure. Clinical hyperbaric oxygen therapy is typically delivered at 2.0 to 2.4 atmospheres absolute (ATA) with 100 percent oxygen, while the wellness industry sells “mild” chambers that top out around 1.3 ATA, often with concentrated rather than pure oxygen. Proponents of each camp claim the evidence is on their side. What has been genuinely scarce is controlled experimental work asking a simpler question: as pressure changes, what actually happens in the brain?
A study published online August 2, 2026, in the journal Neuroscience takes a direct run at that question — in rats. A team at Erciyes University in Kayseri, Türkiye, exposed healthy animals to one hour of hyperbaric oxygen daily for 14 consecutive days at three different pressures: 1.6, 2.0 and 2.4 ATA. They then measured a panel of molecular markers of synaptic plasticity in the hippocampus and tested the animals on two standard memory tasks.
A sweet spot at 2.0 ATA
The results form a curve rather than a straight line. Hippocampal expression of brain-derived neurotrophic factor (BDNF), the transcription factor CREB and its activated form p-CREB all rose significantly under hyperbaric oxygen — with the strongest effect at 2.0 ATA. Genes tied to synaptic structure, including postsynaptic density protein-95, synapsin I and synaptophysin, were also upregulated, which the authors interpret as activation of plasticity-related transcriptional programs.
The inhibitory circuitry shifted too. Parvalbumin expression increased while levels of GAD67, an enzyme involved in synthesizing the inhibitory neurotransmitter GABA, decreased in the 2.0 and 2.4 ATA groups — a pattern the researchers describe as a shift toward a “plasticity-permissive” network state.
Behavior tracked the molecular signal, but only at the middle pressure. Rats treated at 2.0 ATA performed significantly better on the Novel Object Recognition test, a standard assay of recognition memory. The 1.6 ATA group did not show the same improvement, and neither did 2.4 ATA. On the Y-maze test, the 2.0 ATA group showed an upward trend in its discrimination index that did not reach statistical significance.
In other words: in this animal model, more pressure was not better, and less pressure was not enough. The cognitive effect appeared at 2.0 ATA — squarely in the range used in hospital-based hyperbaric departments, and well above what mild wellness chambers deliver.
What a rat hippocampus can — and cannot — tell us
The caveats here are substantial, and the study’s authors’ own framing deserves emphasis. This is a preclinical experiment in healthy rats, not a clinical trial in people. Animal studies of this kind are hypothesis-generating: they map mechanisms and dose-response relationships that human trials can later test. They do not establish that hyperbaric oxygen improves memory in healthy humans, and a 14-day protocol in rodents says nothing about long-term outcomes, optimal session counts, or effects in aging or diseased human brains.
It is also worth noting what the pressure curve implies about risk. Hyperbaric oxygen at higher pressures carries well-documented hazards, including oxygen toxicity seizures, which is one reason clinical protocols are tightly standardized. A finding that 2.4 ATA produced no additional cognitive benefit over 2.0 ATA — while sitting closer to the threshold where oxygen toxicity becomes a concern — is itself a useful data point for protocol design.
The wellness-market mirror
The timing of the paper is notable given the continued boom in consumer hyperbaric use. Mild chambers operating around 1.3 ATA are marketed for cognitive enhancement, focus and “brain optimization,” often with explicit reference to neuroplasticity. The new data do not directly test 1.3 ATA, but the shape of the dose-response curve — no significant recognition-memory effect at 1.6 ATA in this model — sits awkwardly beside claims that pressures lower still will meaningfully remodel the brain.
The U.S. Food and Drug Administration has been blunt about the regulatory reality: hyperbaric oxygen devices are cleared for a defined list of indications — including decompression sickness, carbon monoxide poisoning, certain non-healing wounds and late radiation tissue injury — and the agency states that HBOT has not been proven for the long roster of wellness and neurological uses marketed around it, cognitive enhancement among them. In 2025, the FDA also issued a letter to health care providers warning about serious injuries and deaths linked to fires in hyperbaric devices, urging strict adherence to manufacturer instructions — a reminder that chamber safety, not just efficacy, is part of the pressure conversation.
Why dose-response studies matter
For a field that has long argued about protocols, controlled pressure-comparison experiments are valuable precisely because they are rare. If the Erciyes group’s curve holds up in further work, it would give researchers designing human cognition trials a principled basis for choosing 2.0 ATA — and would sharpen the scientific question hanging over the mild-chamber market. The honest bottom line for now: the brain appears to respond to hyperbaric oxygen in a pressure-dependent way in a rat model, the effect in that model peaks at clinical-grade pressure, and none of this yet constitutes evidence that any chamber, at any pressure, improves memory in healthy people.
Sources
- Baktir MA, et al. Pressure-dependent effects of hyperbaric oxygen on hippocampal CREB-BDNF signaling and associated changes in synaptic plasticity and recognition memory in healthy rats. Neuroscience (2026)
- DOI: 10.1016/j.neuroscience.2026.07.061
- FDA — Hyperbaric Oxygen Therapy: Get the Facts
- FDA — Follow Instructions for Safe Use of Hyperbaric Oxygen Therapy Devices: Letter to Health Care Providers