How brain oxygenation affects mental performance: the fNIRS connection

Breathe in through your nose, filling your lungs and expanding your diaphragm.

Exhale slowly, releasing tension with each breath.

Congratulations. You just did something good for your brain.

Every thought, decision, and action your brain takes depends on oxygen. Deep breathing increases oxygen flow to your brain, activating relaxation responses and supporting cognitive function [1].

Oxygen is essential for converting glucose into energy your brain can use. When oxygen levels drop, your brain’s ability to produce energy weakens, and mental effort can suffer.

Steady oxygen flow encourages healthy circulation to your brain, ensuring oxygen reaches the areas working hardest to keep you sharp, focused, and ready to sustain mental effort. This continuous delivery and use of oxygen is known as brain oxygenation.

What is brain oxygenation?

Brainpower starts with oxygen. Even though your brain makes up only 2% of your body weight, it uses 20% of your oxygen supply [2].

Oxygen helps your brain cells send messages, solve problems, and make decisions. The harder your brain works, the more oxygen it needs. When oxygen levels drop, thinking slows down, focus fades, and decisions become harder [3].

Your brain relies on oxygen to convert key fuel sources into usable energy. Glucose is the primary energy source, providing quick-access fuel for mental processing, while ketones serve as a backup during fasting or extended cognitive effort [4] [5].

Research shows that even a 5% drop in blood oxygen levels can impair mental agility, leading to slower reaction times and reduced memory recall [6]. Since both oxygen and metabolic fuels are essential for brain function, disruptions in either can lead to brain fog, mental fatigue, and decreased processing speed.

Oxygen levels can decrease due to:

• Poor circulation

• Shallow breathing

• Stress

• Environmental factors like high altitudes. 

A better oxygen supply supports sustained attention, problem-solving, and information retention. You can improve oxygen supply through:

• Deep breathing

• Physical activity

• Good posture

These all help enhance circulation and oxygen delivery to your brain [7].

The role of blood, oxygen and the brain 

Blood is the delivery system for oxygen. Oxygen binds to hemoglobin in red blood cells, which carry oxygen-rich blood to the brain. 

Blood flow also removes waste products like carbon dioxide, ensuring the brain maintains the right balance of oxygen and nutrients  [2]. 

Without proper circulation, brain cells cannot produce enough energy to sustain cognitive functions, impacting focus, memory, and decision-making.

Your brain needs:

• Sufficient oxygen to support energy production.

• Blood flow to transport oxygen and fuel.

What controls this blood flow?

• Your brain’s activity itself
  When you think hard, solve problems, or process complex information, certain brain areas demand more oxygen and glucose. 

• In response, your body increases blood flow to those regions—a process called neurovascular coupling, where neurons signal blood vessels to dilate for more oxygen delivery [8].
  

• Automatic regulation processes
  Your body also regulates overall cerebral blood flow through several mechanisms:

• Blood pressure: Ensures stable circulation to the brain [3].

• Oxygen and carbon dioxide levels: High CO₂ levels cause blood vessels to widen, increasing oxygen delivery, while low CO₂ levels restrict blood flow.

• Autoregulation: Blood vessels adjust their diameter in response to oxygen demand, helping the brain maintain stable oxygen levels even during physical activity or stress [8].

The link between oxygenation & mental performance

Think of a marathon runner. Without proper oxygen intake throughout the race, performance suffers. The same applies to your brain.

When working on a complex problem, high oxygen levels help sustain focus and prevent burnout. Low oxygen leads to mental fatigue, reducing problem-solving abilities and reaction times.

How fNIRS tracks oxygenation levels in real time

Functional Near-Infrared Spectroscopy (fNIRS) is a brain imaging technology that helps track how much oxygen your brain is using. 

Since oxygen is essential for thinking, focus, and problem-solving, fNIRS provides valuable insights into brain activity, stress levels, and mental load management [9]. It works by shining light into the scalp and measuring how much is absorbed by the blood in your brain.

Athena, Muse’s newest device, uses EEG in addition to fNIRS technology. 

• fNIRS tracks real-time oxygen usage in the prefrontal cortex, measuring cognitive effort and endurance 

• EEG detects electrical activity, revealing shifts in mental states. 

Together, they show not just when your brain is active, but how efficiently it directs energy during tasks,helping you see when you’re fully engaged and when fatigue sets in.

Read more: Deep dive into fNIRs and EEG here.

How light and blood work together

Your blood carries oxygen using a protein called hemoglobin. Hemoglobin changes color depending on whether it’s carrying oxygen or not. 

Oxygen-rich blood (HbO2) and oxygen-poor blood (HbR) absorb light differently. fNIRS takes advantage of this by sending gentle near-infrared light (invisible to the eye) into the brain and measuring how much light comes back. 

This tells us how much oxygen is being used, which helps determine how hard your brain is working [10].

How light travels through the brain

When near-infrared light enters your scalp, it spreads through your brain tissue. Some of it is absorbed by hemoglobin, and some of it bounces around before being detected by sensors on your head. 

By analyzing how much light is absorbed versus reflected, fNIRS can estimate how much oxygen is being used in different areas of the brain. This gives us a real-time picture of mental effort, focus, and recovery [11].

How we measure oxygen levels

fNIRS uses a formula called the Modified Beer-Lambert Law to turn light measurements into meaningful data. This equation helps adjust for the way light moves through brain tissue, making sure the readings are accurate. In simple terms, it helps convert light signals into numbers that show how oxygen levels change when you’re thinking, learning, or concentrating [12].

How the sensors are arranged

For fNIRS to work properly, tiny light sources and detectors are placed at specific distances on your scalp. These pairs are usually 30–35 mm apart, which allows the light to reach just below the surface of your brain—about 5–8 mm deep. This is the area responsible for higher-level thinking, decision-making, and focus. By tracking blood flow and oxygen levels in this region, fNIRS can measure mental effort and how well your brain recovers from cognitive strain [13]. 

Why this matters

By using fNIRS, we can understand when our brains are working too hard, when they need a break, and how efficiently they recover. This is especially useful for tracking focus, preventing burnout, and optimizing cognitive performance. Whether you're working, learning, or managing stress, fNIRS provides real-time feedback on how your brain is performing.

Tracking brain oxygenation to optimize performance with Athena

Athena utilizes fNIRS sensors to monitor oxygenated blood flow in the prefrontal cortex, the area responsible for focus, decision-making, and cognitive endurance. 

In the Mental Strength program, users guide a digital owl forward using sustained mental focus. Athena’s fNIRS sensors track oxygenated blood flow in the prefrontal cortex in real time—when concentration increases, so does brain oxygenation, and the owl flies higher and faster.

Rather than just monitoring brain activity, Athena actively trains your brain to use oxygen more efficiently, fostering enhanced focus, mental resilience, and sustained performance under pressure.

Your Athena session: blood oxygenation & mental strength metrics

After each session, Athena delivers a comprehensive breakdown of your brain’s performance, including:

1. Mental Strength Score – A measure of your brain’s ability to sustain mental effort over time. A higher score means you maintained cognitive endurance for longer, building focus, stamina, and resilience under pressure.
   
   

2. Blood O₂ Levels – A detailed graph of how your brain directed energy during Mental Strength Sessions by tracking oxygenated blood flow to the prefrontal cortex.
   
   

• Oxygenated blood (red line): Increases when your brain is working harder, delivering more energy for sustained effort.

• Deoxygenated blood (blue line): Decreases as your brain efficiently utilizes oxygen to maintain focus and endurance.

This provides real-time insights into how your brain performs under pressure, helping you refine your cognitive training strategies.

The bottom line: what actually drives mental performance?

Your Mental Strength Score isn’t about how much oxygen you take in—it’s about how efficiently your brain uses that oxygen during focused effort.

Deep breathing ensures your brain has the oxygen it needs, but it doesn’t push the owl forward. What moves the owl—and drives your score—is sustained mental effort, as captured by real-time EEG and fNIRS signals.

In summary, your brain’s ability to sustain mental effort depends on a constant flow of oxygen:

• Oxygen intake through breathing provides the oxygen your brain needs to support energy production.

• Blood flow transports oxygen and essential fuel sources like glucose or ketones to the brain.

• The brain uses oxygen to convert those fuels into energy, sustaining focus, decision-making, and problem-solving.

Smarter training starts with better insights

Your brain is like any other muscle—it performs best when it gets the right fuel. 

Understanding brain oxygenation is just like a runner understanding their breath. Once they can work with it, they can run miles. With Athena, you gain access to real-time data that helps you train smarter, focus longer, and restore mental sharpness faster, improving your overall mental fitness.

Whether you’re an entrepreneur looking to stay sharp, a biohacker seeking the next brain-boosting strategy, or someone aiming to reduce mental fatigue, Athena’s data-driven approach will help you reach your goals - one breath at a time.

Try Athena now and be one of the first to train your brain with fNIRS in the comfort of your own home.

Sources 

[1] University of Toledo Counseling Center. (n.d.). Deep breathing and relaxation. University of Toledo. Retrieved from https://www.utoledo.edu/studentaffairs/counseling/anxietytoolbox/breathingandrelaxation.html 

[2] Raichle, M. E., & Gusnard, D. A. (2002). Appraising the brain's energy budget. Proceedings of the National Academy of Sciences, 99(16), 10237–10239. https://doi.org/10.1073/pnas.172399499

[3] Ainslie, P. N., & Subudhi, A. W. (2014). Cerebral blood flow at high altitude. High Altitude Medicine & Biology, 15(2), 133–140. https://doi.org/10.1089/ham.2014.1401

[4] Mergenthaler, P., Lindauer, U., Dienel, G. A., & Meisel, A. (2013). Sugar for the brain: The role of glucose in physiological and pathological brain function. Trends in Neurosciences, 36(10), 587–597. https://doi.org/10.1016/j.tins.2013.07.001 

[5] Poff, A. M., Koutnik, A. P., Egan, B., & D'Agostino, D. P. (2019). Ketone bodies as a therapeutic for Alzheimer's disease. Neurotherapeutics, 16(3), 665–674. https://doi.org/10.1007/s13311-019-00752-9

[6] McMorris, T., Hale, B. J., Barwood, M., Costello, J., & Corbett, J. (2017). Effect of acute hypoxia on cognition: A systematic review and meta-regression analysis. Neuroscience & Biobehavioral Reviews, 74, 225–232. https://doi.org/10.1016/j.neubiorev.2017.01.019

[7] Barrett, D. W., & Gonzalez-Lima, F. (2013). Transcranial infrared laser stimulation produces beneficial cognitive and emotional effects in humans. Neuroscience, 230, 13–23. https://doi.org/10.1016/j.neuroscience.2012.11.016

[8] Iadecola, C. (2017). The neurovascular unit coming of age: A journey through neurovascular coupling in health and disease. Neuron, 96(1), 17–42. https://doi.org/10.1016/j.neuron.2017.07.030

[9] Herold, F., Wiegel, P., Scholkmann, F., & Müller, N. G. (2018). Applications of functional near-infrared spectroscopy (fNIRS) in exercise–cognition research: A systematic, methodology-focused review. Journal of Clinical Medicine, 7(12), 466. https://doi.org/10.3390/jcm7120466

[10] Pinti, P., Aichelburg, C., Lind, F., Power, S. D., Swingler, E., Merla, A., Hamilton, A., & Gilbert, S. J. (2020). Using fiberless, wearable fNIRS to monitor brain activity in real-world settings. Scientific Reports, 10, 17319. https://doi.org/10.1038/s41598-020-73933-z

[11] Boas, D. A., Elwell, C. E., Ferrari, M., & Taga, G. (2014). Twenty years of functional near-infrared spectroscopy: Introduction for the special issue. NeuroImage, 85, 1–5. https://doi.org/10.1016/j.neuroimage.2013.11.033 

[12] Scholkmann, F., Kleiser, S., Metz, A. J., Zimmermann, R., Pavia, J. M., Wolf, U., & Wolf, M. (2014). A review on continuous wave functional near-infrared spectroscopy and imaging instrumentation and methodology. NeuroImage, 85, 6–27. https://doi.org/10.1016/j.neuroimage.2013.05.004pubmed.ncbi.nlm.nih.gov+2

[13] Brigadoi, S., & Cooper, R. J. (2015). How short is short? Optimum source-detector distance for short-separation channels in functional near-infrared spectroscopy. Neurophotonics, 2(2), 025005. https://doi.org/10.1117/1.NPh.2.2.025005PubMed Central+2