The science of EEG + fNIRS: Why combining these technologies enhances mental fitness

We’ve all been there - struggling to focus, feeling mentally drained, wondering why our brain isn’t keeping up. Despite the mental overload, stress, and endless to-do lists, we rarely think about what it takes to keep mentally fit. 

Cognitive decline already affects 6 million Americans, and by 2060, that number is expected to double [1]. Research shows that cognitive decline isn’t inevitable - early intervention and lifestyle changes can help slow the process, but most people focus on physical health while neglecting their brain health [2]. 

With brain function decline beginning in middle age and dementia cases on the rise  [1], brain training has never been more essential. With the help of cutting edge tools like Muse S Athena your best thinking days are ahead. Here’s the science to prove it.

What is EEG (Electroencephalography)?

Invented a century ago, electroencephalography (EEG) records the brain’s electrical activity. With the ability to capture rapid electrical signals at the millisecond level, EEG provides a powerful window into dynamic mental states like focus, relaxation, and stress [3][4].

EEG is widely used to study brain function due to its non-invasiveness, cost-effectiveness, portability, and long-term monitoring capabilities. It tracks the full spectrum of brainwaves, including:

• Theta waves, associated with deep relaxation and creativity.

• Alpha waves, linked to calm alertness and attentional clarity.

By analyzing these brainwaves, EEG helps determine how well your brain recovers after intense effort—similar to how your body cools down after a workout.

What once required complex lab setups and lengthy reports is now available in easy-to-use consumer technology, delivering real-time brain activity insights straight to your smartphone. All Muse devices track brainwave insights through four unique EEG biofeedback experiences: Mind, Heart, Body, and Breath.

The Mind Biofeedback experience helps you stay in a calm, focused state through neurofeedback training, improving overall mental clarity. A sharp, focused mind enhances decision-making, problem-solving, and cognitive performance, keeping distractions and fatigue at bay.

How does EEG work? 

Think of EEG (electroencephalography) like a microphone for your brain. It listens to the electrical signals that your brain cells (neurons) use to communicate with each other.

Here’s how it works:

1.  Your brain creates tiny electrical signals – When neurons send messages, they generate small electrical pulses. These pulses happen in patterns, which scientists call brain waves.

2. EEG sensors pick up these signals – Small sensors (electrodes) placed on your scalp detect these electrical signals. They don’t send electricity into your brain—just listen, like a microphone picking up sound.

3. The signals are recorded and analyzed – The EEG device captures brain activity in real time, showing different types of brain waves, such as:

1. Beta waves (when you’re focused and thinking)

2. Alpha waves (when you’re relaxed)

3. Theta waves (when you’re drowsy or meditating)

4. Delta waves (when you’re in deep sleep)

4. EEG helps understand brain states – By analyzing the patterns of brain waves, EEG can tell whether you’re focused, relaxed, stressed, or even how well you’re sleeping.

In short, EEG gives you a real-time look at how active your brain is, helping you train focus, relaxation, and cognitive performance.

What is fNIRS (functional near-infrared spectroscopy)?

While EEG measures mental clarity by tracking how efficiently your brain processes tasks, fNIRS (functional near-infrared spectroscopy) focuses on mental strength and endurance, showing how much energy your brain uses to power through cognitive challenges. Pairing EEG with fNIRS provides a complete picture of cognitive performance.

fNIRS measures blood flow and oxygenation levels in your prefrontal cortex, showing how well your brain is fueled to handle stress, sustain attention, and recover. When you tackle a challenging task, your brain demands more oxygen to power cognitive effort. Just like muscles need oxygen for endurance, the brain relies on it to sustain focus and efficiency. Higher oxygenation levels mean your brain can manage mental workload more effectively, reducing strain and fatigue. 

By monitoring oxygenated blood flow (HbO2) to the prefrontal cortex, fNIRS reveals how efficiently your brain is allocating resources. Improved oxygenation boosts mental endurance, self-regulation, and cognitive flexibility, allowing you to sustain focus and fight cognitive fatigue. It is especially useful for studying brain health in everyday environments [5]

Unlike EEG, which tracks electrical activity with electrodes, fNIRS works by projecting near-infrared light into the front of the brain and detecting how much is absorbed by oxygenated and deoxygenated blood [6]. This process, known as neurovascular coupling, shows which areas of the brain are active during cognitive tasks. As neurons fire, they signal nearby blood vessels to deliver more oxygen and nutrients, fueling mental performance [7]

Essentially, fNIRS lets us "eavesdrop" on the brain's resource management system, tracking how efficiently it fuels itself under cognitive load. Training your brain to improve oxygenation capacity strengthens mental fitness, resilience, and long-term cognitive performance.

Why combine EEG + fNIRS together?

Cognitive performance - a holistic view 

The same way a balanced fitness routine consists of exercises that improve strength, endurance, and recovery, cognitive fitness requires a variety of training methods as well. Mental clarity, mental strength, and mental recovery are key pillars in your mental fitness game. EEG and fNIRS work together to provide a complete picture of brain performance allowing you to measure and train different areas of your cognitive performance. 

With EEG-powered real-time neurofeedback, you can sharpen focus and sustain attention when it matters most. fNIRS tracking measures mental effort and stamina, helping you push cognitive limits while avoiding burnout. Athena also supports brain recovery with sleep tracking and Digital Sleeping Pills, ensuring your mind stays sharp and resilient over time.

Faster and more accurate insights 

EEG works like a live radio broadcast, capturing every brain signal in real time, within milliseconds [4]. This makes it ideal for tracking mental clarity, or how efficiently the brain shifts between focus and relaxation. It detects moment-to-moment changes, revealing how neurons communicate instantly, making it a powerful tool for measuring attention, cognitive workload, and reaction speed - all factors to make up mental clarity [8].

fNIRS, on the other hand, works like a video replay with instant highlights—tracking real-time changes in oxygenation but with a slight delay compared to EEG. It measures oxygen-rich blood flow (HbO2) to show how much energy the brain is using during cognitive effort, offering an acute view of mental strength and endurance -  the key to sustaining focus and problem-solving. While EEG provides second-by-second neural activity, fNIRS captures short-term physiological responses, showing how the brain fuels itself under cognitive load [9]. 

Using both EEG and fNIRS to track real-time performance in different ways, you gain insight into a more complete picture of cognitive performance and can apply targeted cognitive training that enhances focus, endurance, and recovery.

Better tracking & reduced noise

EEG and fNIRS are powerful on their own, but they each have limitations.

• EEG is sensitive to electrical noise and muscle movements (like blinking), which can interfere with signals.

• fNIRS can be influenced by blood flow changes unrelated to cognitive activity, such as position changes, breathing or heart rate fluctuations [7].

When used together, they correct each other’s weaknesses and provide more reliable insights. For example, studies have shown above 96% accuracy levels in cognitive classification tasks when EEG and fNIRS are used together [3]. The fusion of these technologies yields the most reliable data since they fill in the gaps where one technology is weaker [10].

Real-world applications

EEG and fNIRS together provide a clearer, more detailed picture of how the brain works during different tasks. 

For example, a study on movement and mental imagery [8] found that combining these technologies revealed brain activity previously undetectable, specifically in the Action Observation Network (AON). This system activates when we watch others move, allowing us to mentally rehearse and refine those actions. 

The AON plays a key role in motor learning and skill acquisition, as it helps translate observed actions into internalized movement patterns. Research suggests that this mechanism is essential not only for athletes and performers refining their techniques but also for rehabilitation, as patients recovering from motor impairments can strengthen neural pathways simply by observing movement. 

Additionally, the AON is linked to social cognition, as it enables us to understand and predict the intentions of others based on their actions. Studies indicate that engaging the AON through visualization can enhance performance similarly to physical practice, reinforcing the idea that mental training is a powerful tool for skill development. By tracking this kind of real-time brain engagement, pairing EEG fNIRS provide deep insights into mental fitness, showing when your brain is truly “in the game.

From research to real-world impact

This technology is shaping the future of how we understand and optimize the brain. It’s paving the way for advancements in:

• Performance optimization: Enhancing mental load management and productivity in high-pressure workplaces and high-performance environments by monitoring cognitive workload for peak performance [4].

• Sleep Health & diagnostics: Tracking brain oxygenation and SpO₂ levels to provide deeper insights into potential sleep disorders like sleep apnea, delivering more accurate measurements than wrist or finger sensors. These insights help guide personalized interventions for improved sleep quality and recovery.

• Brain health & clinical research: Supporting real-time interventions for age-related cognitive decline and advancing research from assessing infant and geriatric populations to studying neurological conditions [6]. 

• Neurotechnology & recovery solutions: Driving progress in Brain-Computer Interfaces (BCIs) that enhance communication between the brain and external devices, while supporting neurorehabilitation efforts by tracking cognitive workload during recovery from neurological injuries.

Muse is trusted by hundreds of research labs and featured in over 200 third-party research papers. With Muse S Athena, brain tracking becomes more accessible, precise, and impactful, redefining the future of neuroscience research.  

How Athena uses EEG + fNIRS for brain training

With over half a million users—and some so dedicated they’ve used Muse for 2,000 days straight!—Muse knows how transformative neurofeedback training can be on brain health. 

Muse S Athena is the first consumer wearable to combine EEG and fNIRS sensors, in a light-weight easy to use device, expanding on the award-winning features of Muse 2 and Muse S (Gen 2). By tracking both brainwave activity (EEG) and brain oxygenation (fNIRS), Athena provides a complete view of cognitive performance.

It offers brain-powered meditation, sleep support, and now, eyes-open cognitive training for real-time mental performance enhancement. Athena transforms real-time brain activity into actionable insights, personalized training, and measurable progress—all powered by Muse’s AI-driven Foundational Brain Model (FBM). Trained on 80,000 curated sessions from the world’s largest EEG database, FBM delivers precision neurofeedback to optimize mental fitness.

Athena’s interactive, eyes-open training mode helps users actively engage their brains through dynamic fNIRS-powered neurofeedback. It allows them to use their minds to power an owl in flight within the Muse app, turning brain training into a truly immersive experience.

fNIRS Neurofeedback (Eyes-Open) vs. EEG Neurofeedback (Eyes-Closed)

Previous Muse devices focused on a EEG-powered biofeedback experience where the user's eyes were closed, designed to monitor brain and body activity during focused attention training through mindfulness. This approach rewarded deep relaxation and focus with the calming sounds of nature and birds chirping.

With Muse S Athena, we’ve added a new eyes-open mental strength training experience, designed for active, engaged brain exercises. While still offering the eyes-closed neurofeedback users know and love, Athena now features an interactive training session where an owl speeds up or slows down based on your cognitive effort, providing immediate feedback on mental effort with your eyes open.

Cognitive Fitness: a vision for the future

Brain optimization is set to reach new heights with the combination of EEG and fNIRS. This dual approach is changing how we measure, train, and enhance brain function. With real-time neurofeedback and personalized training programs, wearable neurotechnology like Muse S Athena goes beyond brain tracking.

We’re entering an era where understanding and training the brain will become as common and important as physical fitness. From peak performance and stress management to neurorehabilitation, this next generation of brain optimization is set to become an essential part of everyday life.

The future of brain training is here. And this time, we’re doing it with our eyes open. Start your own mental fitness journey today with Muse S Athena. Shop now.

References: 

[1] Brookmeyer, R., Abdalla, N., Kawas, C. H., & Corrada, M. M. (2018). Forecasting the prevalence of preclinical and clinical Alzheimer's disease in the United States. Alzheimer's & Dementia, 14(2), 121–129. https://doi.org/10.1016/j.jalz.2017.10.009

[2] Coresh, J., et al. (2025). United States dementia cases estimated to double by 2060. Nature Medicine. https://nyulangone.org/news/united-states-dementia-cases-estimated-double-2060

[3] PMC. (2023). Wearable, Integrated EEG–fNIRS Technologies: A Review. Retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC8469799/ 

[4] Nature. (2023). Simultaneous multimodal fNIRS-EEG recordings reveal new insights. Retrieved from https://www.nature.com/articles/s41598-023-31609-5

[5] Boston University Neurophotonics. (n.d.). fNIRS research at Boston University Neurophotonics Center. Retrieved from https://www.bu.edu/neurophotonics/research/fnirs/

[6] Artinis. (2023). Introduction to multimodal fNIRS — EEG measurements. Retrieved from https://www.artinis.com/blogpost-all/2023/introduction-to-multimodal-fnirs-eeg-measurements

[7] PubMed. (2023). Simultaneous multimodal fNIRS-EEG recordings reveal new insights. Retrieved from https://pubmed.ncbi.nlm.nih.gov/36991003/

[8] Frontiers in Neurorobotics. (2022). Multi-Modal Integration of EEG-fNIRS for Characterization of Brain Function. Retrieved from https://www.frontiersin.org/journals/neurorobotics/articles/10.3389/fnbot.2022.823435/full

[9] Bitbrain. (2023). Fusion of fNIRS and EEG: A step further in brain research. Retrieved from https://www.bitbrain.com/blog/fusion-fnirs-eeg-brain-activity-research

[10] TMSi. (2023). Multimodal Measurement: Integration of EEG & fNIRS. Retrieved from https://info.tmsi.com/blog/eeg-fnirs-integration