fNIRS and Systemic Physiology: Why Measuring the Body Improves Neuroimaging Reliability

fNIRS is a powerful technology because it allows researchers to measure cortical hemodynamic responses in more natural situations: listening to speech, interacting, learning, moving, or participating in collective tasks. But the study by Mollison, Rodriguez, Metzger, and Shader shows an essential point: for fNIRS to become more reliable, we also need to measure the body.

The scientific question of the article is excellent: does correcting systemic physiological signals improve the test–retest reliability of fNIRS during an auditory passive-listening task? To answer this, the researchers evaluated 15 participants across two identical sessions, separated by up to one week, while they listened to sentences in English and Spanish. Speech-evoked activity was measured with fNIRS, and reliability across sessions was assessed using the intraclass correlation coefficient, or ICC.

The study deserves praise because it addresses a real methodological problem. Many fNIRS studies interpret oxyhemoglobin variation as if it came only from the brain. But the signal passes through the scalp, superficial blood vessels, skull, and cortical tissue. Therefore, respiration, heart rate, body temperature, GSR, SpO₂, PPG, and extracerebral noise can all modify the data. The article shows that correcting these signals is not just a technical detail: it is central to neuroscientific reliability.

The equipment used is especially relevant for BrainLatam2026: NIRSport2 + NIRx WINGS, from NIRx. The NIRSport2 system used 16 LED sources, two wavelengths — 760 and 850 nm —, 16 detectors, and a sampling rate of 5.1 Hz. The study also included 38 source-detector pairs of approximately 3 cm and 8 short-separation channels placed 8 mm from the sources to capture extracerebral scalp activity.

The systemic physiology was recorded with NIRx WINGS, measuring PPG, heart rate, SpO₂, body temperature, GSR, and respiration. This is very important because fNIRS is not measuring an isolated brain. It measures the brain inside a living body, with circulation, breathing, autonomic regulation, and physiological microvariations happening at the same time.

The study compared three analysis models: no correction, short-channel correction, and short-channel + tCCA correction. The tCCA model incorporated body physiology signals with temporal lags, allowing the analysis to better model the delay between physiological changes and their impact on the fNIRS signal.

The results were very clear. Without correction, the ICC was 0.835. With short-channel correction, it increased to 0.950. With short channels + tCCA, it reached 0.997. In other words, all models showed high group-level reliability, but systemic physiological correction produced the best test–retest reliability.

Figure 3 of the article is very educational: without correction, the speech-evoked response appeared inverted or contaminated; with short-channel correction and especially with short-channel + tCCA, positive HbO activity became more coherent with the primary auditory cortex. Figure 4 also shows reduced variability between sessions when correction models were applied. This shows that measuring the body does not “complicate” fNIRS — measuring the body cleans the signal.

From the BrainLatam2026 perspective, this study confirms a central idea: the Damasian Mind cannot fit into disembodied neuroimaging. Interoception, proprioception, breathing, body temperature, skin conductance, and cardiovascular rhythm are not only noise. They are part of the bodily state that enables or limits attention, listening, presence, and cognitive reorganization.

The avatar-lens here can be Jiwasa, because listening is always a body-to-body phenomenon. Even in a passive task, the whole organism participates: the ear receives, the auditory cortex processes, breathing changes, the autonomic system adjusts, and the body decides how much presence it can sustain. fNIRS measures the cortex, but the whole body participates in the response.

For APUS, as body-territory, the study is also very strong. The scalp, peripheral circulation, breathing, and skin are not external obstacles to the brain. They are the physiological territory through which the data passes. When we measure this territory, neuroimaging interpretation becomes more honest.

The generous decolonial critique is that this article strengthens a less “corticalist” neuroscience. Instead of searching for a pure brain, separated from the body, it shows that reliability improves when we accept systemic complexity. This comes very close to an embodied neuroscience: brain, body, and environment as a living system.

A future BrainLatam2026 experimental design could use NIRSport2 + NIRx WINGS + EEG + EMG in collective listening, classroom, music, or performance tasks. The question would be: when several bodies listen together, does the synchrony observed in fNIRS come from the cortex, shared breathing, autonomic state, or a real integration between brain-body-territory?

The bridge with DREX Cidadão appears when we remember that physiology is also shaped by public policy. Insecurity, hunger, debt, fear, and lack of belonging alter breathing, heart rate, sleep, muscle tension, and attentional availability. A society in anergy produces bodies less available for Zone 2. Measuring the body helps show that social suffering is not abstract: it enters physiology.

The article itself recognizes important limitations: small sample size, the need for more sessions, greater diversity in hair types and scalp skin color, and the future inclusion of measures such as paCO₂. This point is very relevant, because breathing and CO₂ can directly alter cerebral hemodynamics, especially in auditory and speech tasks.

Closing:
This study shows that fNIRS becomes more reliable when it stops trying to measure an isolated brain. The neuroimaging of the future will be systemic: fNIRS with short channels, respiration, GSR, PPG, SpO₂, temperature, HRV/RMSSD, EMG, and movement. For BrainLatam2026, this is more than a technical advance. It is a passage toward an embodied, decolonial, and honest neuroscience: measuring the brain inside the body, the body inside the territory, and the territory inside real life.

Single Reference
Mollison, A. A., Rodriguez, E. R., Metzger, A., & Shader, M. J. (2026). Group-level test–retest reliability assessment using systemic physiology augmented functional near-infrared spectroscopy during a passive-listening task. Neurophotonics, 13(1), 015005. doi:10.1117/1.NPh.13.1.015005.