Functional Near Infrared Spectroscopy (fNIRS) for Assessing Mental Workload of Humans in Terrestrial and Microgravity Environments
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gagnon-agagnon-phd-aeroastro-2026-thesis.pdf
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Author(s)
Gagnon, Amelia T.
Advisor(s)
Cahoy, Kerri
Desimone, Robert
Newman, Dava
Stankovic, Aleksandra
Date Issued
May 2026
Publisher
Massachusetts Institute of Technology
Abstract
The monitoring and quantification of mental workload is a highly sought after capability for use in roles where performance is critical, such as for astronauts or pilots, and has application in all industries where there is a human in the loop. One technology for assessing mental workload is functional near-infrared spectroscopy (fNIRS), a portable device that uses near-infrared light in wavelengths sensitive to oxygenated (HbO) and deoxygenated hemoglobin (HbR) to make assessments of underlying tissue. When applied to the skull non-invasively, the technology is able to monitor changes in cerebral blood oxygenation as a proxy for neuronal activation [1].
Over the decades of mental workload research, a set of criteria have been developed to assist with selecting a mental workload monitoring method. This work assesses fNIRS as a mental workload monitoring device in the context of astronauts on-orbit, during long-duration spaceflight, and for use in a Lunar or Martian environment with a focus on three criteria: diagnosticity, which is determining source and degree of mental workload, performance ability in non-Earth gravities, and ability to quantify mental workload and learning in a real-world task setting.
To best evaluate each criterion, three experimental protocols are designed and performed. Study #1: Pilots Flying Simulated Approaches investigates the cerebral hemodynamic response function of pilots (n=10) flying approach-to-landings in a flight simulator, over a task duration of approximately 2 min. Bilateral observation of the prefrontal cortex is selected as the region of interest since this region is responsible for decision making processes and working memory. When assessing three levels of simulated approach difficulty, statistically significant concentrations were observed in both HbO and HbR channels. HbO concentrations increased in intensity and number of regions as the 3 difficulty levels increased, with locations of interest in the dorsolateral prefrontal cortex, pars triangularis area, and frontopolar areas. HbR channels showed decreasing values in the dorsomedial prefrontal cortex.
Study #2: Parabolic Flight analyzes how acute microgravity, hypergravity, Martian, and Lunar gravity forces on a participant (n=1), as induced by parabolic flight, affect fNIRS measurements observed at rest and while performing a visual n-back (2-back) task designed to increase mental workload. N-back tasks are a common way to increase mental workload by having a participant iteratively hold a set number of items in their working memory. In a 2-back task, participants must recall if a newly-introduced item matches the item introduced 2 iterations previous. The targeted region of interest in this protocol is also the prefrontal cortex, and a montage design is selected to overlap with identical locations found in the third experiment, which provides a robust control group for further comparison. It was found that different induced gravities result in different activations for the same task, even when induced gravity is controlled for. While there were fewer significant channels in the Martian parabolas. Lunar and microgravity parabolas saw HbO decreases primarily on the left dorsolateral prefrontal cortex with HbO increases in the dorsomedial prefrontal cortex and frontopolar areas. HbR responses varied to a wider range across in both increases and decreases across parabolas.
Study #3: Head-Down Tilt (HDT) assesses the suitability of fNIRS as a tool for diagnosticity of mental workload sources utilizing both visual and audio mental workload stimuli in repeated n-back tasks where the stimuli and the task demands presented to the participant (n=24) are varied.
Optodes are applied to the prefrontal cortex and the right temporal lobe, focusing on the superior temporal gyrus, middle temporal gyrus, and Broca's area for their role in audio stimuli processing.
The experiment is performed in both a seated and head down tilt -6 degree posture. The seated posture provides a control for fNIRS mental workload assessments made in Earth-gravity and the head-down tilt posture elicits the same circulatory fluid shift as seen in microgravity to make further cross-comparisons to the parabolic flight. When performing the same task across both seated and HDT postures, HDT showed significant increases in HbR concentrations of the dorsomedial prefrontal cortex. These channels increased in number as the task difficulty increased. When the passive audio and audio 2-back were introduced, HbR channels in the subcentral area showed a higher sensitivity to passive audio while HbO channels in the pars triangularis/Broca's area showed higher sensitivity to the audio 2-back task.
Research presented in this thesis contributes to the characterization of fNIRS technology in the context of mental workload for future applications in both terrestrial and microgravity environments.
MIT Department
Massachusetts Institute of Technology. Department of Aeronautics and Astronautics
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