Wearable Brain Sensor Could Bring Real-Time Cognitive Fatigue Monitoring Into Everyday Environments

Source: MDPI AG, by Mauro Victorio; James Dieffenderfer; Tanner Songkakul; Josh Willeke; Alper Bozkurt; Vladimir A. Pozdin (September 22, 2026). AI-generated summary by biochip.com, published September 24, 2026. Not independently reviewed.

A bandage-sized wireless sensor developed by researchers including Vladimir A. Pozdin of Florida International University and Alper Bozkurt of North Carolina State University measures brain-related changes in blood oxygenation while a person moves freely. The device uses functional near-infrared spectroscopy, or fNIRS, an optical technique that shines safe levels of near-infrared light into tissue and analyzes the light that returns. Built on a 19 x 44 mm circuit board and secured to the forehead with medical film dressing, the system combines light sources, detectors, signal processing, Bluetooth Low Energy communication, and a battery. In tests involving blood-flow interruption, breath-holding, and mental arithmetic, it detected hemodynamic responses, meaning changes in blood oxygenation associated with brain activity. One participant showed a changing response across repeated arithmetic cycles that the researchers linked to fatigue. The prototype is not a fatigue alarm and has not been shown to warn pilots, air traffic controllers, students, or other workers before performance declines. Still, its small size, wireless design, and roughly 50-hour battery life suggest a path for studying cognitive workload beyond the controlled setting of a laboratory.

A forehead sensor that uses light

The basic principle resembles shining two differently colored flashlights through a thin part of the body, then measuring how much light comes back. Blood absorbs light differently depending on whether hemoglobin, the oxygen-carrying molecule in red blood cells, has oxygen attached to it. That difference gives fNIRS a way to track relative changes in oxygenated and deoxygenated hemoglobin in the brain.

The wearable system uses light-emitting diodes, or LEDs, at wavelengths of 660 nanometers and 840 nanometers. Those wavelengths provide the contrast needed to distinguish changes in oxygenated and deoxygenated hemoglobin. Because the sensor sits on the forehead, it measures optical signals from tissue beneath the placement site and calculates oxygenation changes associated with neural activity.

Designed for movement, not a lab bench

Conventional brain-monitoring studies often happen in tightly controlled environments where participants remain relatively still. This platform was designed to make measurements while people can move normally, an important feature for studying attention and mental workload during activities that unfold outside a laboratory.

The complete system includes a 500 milliamp-hour battery that provided about 50 hours of continuous operation when sampling at 10 hertz, or 10 measurements per second. Bluetooth Low Energy allows the device to transmit data wirelessly while preserving battery power. Together, those components turn the sensor into a compact research platform rather than a wired instrument tied to a room.

Measuring the device's light output

Before using an optical sensor on the body, researchers need to know precisely how much light its LEDs emit. The team characterized both the spectral output, or distribution of light across wavelengths, and the total irradiated power from the 660 nm and 840 nm LEDs.

For that work, the researchers used StellarNet's IS6 LED Measurement System with a 6-inch integrating sphere. An integrating sphere captures light from many directions, much like a white, reflective room gathers light from a lamp, allowing measurement of total optical output. The resulting measurements helped determine hemoglobin optical constants and set LED-drive safety limits using IEC 62471, a standard addressing photobiological safety of lamps and lamp systems.

Testing responses to cognitive work

The researchers tested the system with arterial occlusion, breath-holding, and cognitive-workload experiments. Arterial occlusion temporarily restricts blood flow, while breath-holding changes the body's oxygen and carbon-dioxide balance. These tests offered ways to observe whether the sensor could register physiological changes in its optical signals.

In the cognitive experiment, participants repeatedly completed two-digit and three-digit arithmetic tasks while wearing the device. The team reported measurable hemodynamic responses associated with the mental work. In one participant, those responses shifted over repeated cycles in a pattern the researchers said correlated with fatigue, a signal that may be worth studying in larger real-world datasets.

What the prototype does and does not do

Cognitive fatigue can affect reaction time and decision-making, but recognizing its onset objectively is difficult. A wearable sensor that records brain-related oxygenation during demanding tasks could help researchers investigate when workload rises, how fatigue develops, and how recovery appears in people performing real activities.

That is different from an operational warning system. The current work does not establish that the device can diagnose fatigue or reliably tell a worker that impaired performance is imminent. It instead demonstrates that a compact, wireless fNIRS platform can record cerebral oxygenation changes associated with activity and can operate in settings less restricted than a conventional laboratory.

Recognition for wearable spectroscopy

The work was published in the peer-reviewed journal Biosensors in 2025 and received third place in StellarNet's 2026 Spectroscopy Application Challenge. The annual program recognizes applications of spectroscopy, the measurement of how matter interacts with light, and related optical technologies.

Jason Pierce, president of StellarNet, said the prospect of using light to study cognitive workload during work, learning, or performance opens a different category of measurement. The recognition reflects the role that careful optical characterization played in the device's development, from measuring LED output to defining safe operating conditions.

Why This Matters

Wearable brain sensing could shift research on attention and fatigue from brief, artificial tests toward longer observations in environments where sustained concentration matters. The key appeal is not that this sensor has solved fatigue detection, but that it packages optical measurement, data collection, wireless communication, and battery power into a forehead-mounted device small enough for unrestricted use.

Such measurements could eventually support research in mission-critical work, training, education, and human performance, where the timing and context of mental strain matter. The next challenge is to determine whether the patterns detected by the platform consistently map to meaningful fatigue, workload, and recovery across many people and everyday conditions.

As researchers collect larger datasets in less controlled settings, they may be able to test whether continuous fNIRS signals can separate ordinary fluctuations in brain oxygenation from changes that matter for performance. For now, the device provides a practical tool for asking that question while people move through the tasks that make cognitive fatigue difficult to study.

Topics: Biosensors · Brain & neurological health

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