The relationship between brain cortical activity and brain oxygenation in the prefrontal cortex during hypergravity exposure

Abstract

Artificial gravity has been proposed as a method to counteract the physiological deconditioning of long-duration spaceflight; however, the effects of hypergravity on the central nervous system has had little study. The study aims to investigate whether there is a relationship between prefrontal cortex brain activity and prefrontal cortex oxygenation during exposure to hypergravity. Twelve healthy participants were selected to undergo hypergravity exposure aboard a short-arm human centrifuge. Participants were exposed to hypergravity in the +Gz axis, starting from 0.6 +Gz for women, and 0.8 +Gz for men, and gradually increasing by 0.1 +Gz until the participant showed signs of syncope. Brain cortical activity was measured using electroencephalography (EEG) and localized to the prefrontal cortex using standard low-resolution brain electromagnetic tomography (LORETA). Prefrontal cortex oxygenation was measured using near-infrared spectroscopy (NIRS). A significant increase in prefrontal cortex activity (P < 0.05) was observed during hypergravity exposure compared with baseline. Prefrontal cortex oxygenation was significantly decreased during hypergravity exposure, with a decrease in oxyhemoglobin levels (P < 0.05) compared with baseline and an increase in deoxyhemoglobin levels (P < 0.05) with increasing +Gz level. No significant correlation was found between prefrontal cortex activity and oxy-/deoxyhemoglobin. It is concluded that the increase in prefrontal cortex activity observed during hypergravity was most likely not the result of increased +Gz values resulting in a decreased oxygenation produced through hypergravity exposure. No significant relationship between prefrontal cortex activity and oxygenation measured by NIRS concludes that brain activity during exposure to hypergravity may be difficult to measure using NIRS. Instead, the increase in prefrontal cortex activity might be attributable to psychological stress, which could pose a problem for the use of a short-arm human centrifuge as a countermeasure.

The effects of varying gravito-inertial stressors on grip strength and hemodynamic responses in men and women

“…To achieve statistical significance, this analysis yielded an estimated number of participants equal to 12. This value is compatible with previous studies in which cognitive functions and hemodynamic parameters were assessed during varying gravitational loading (White et al 2005, 2012, 2018; Smith et al 2013; Schneider et al 2014; Goswami et al 2015a, b; Evans et al 2015; Barbiero et al 2017; Verma et al 2018) ( N  = 6 to 20). We nevertheless decided to apply a safety margin to these values and recruited 19 participants.…”

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Imaging Brain Function with Functional Near-Infrared Spectroscopy in Unconstrained Environments

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Simultaneous measurement of electroencephalography and near-infrared spectroscopy during voluntary motor preparation

“…The onset of the movement was defined as the time when the differential waveform of EMG was over the three-sigma limits. Outlier trials were excluded from analysis according to the following steps: (1) we determined a threshold for the artifact as ± 60 μV; (2) the epochs where EEG signals of more than 3 electrodes exceeded the threshold before movement onset were selected; (3) the selected trial that was also visually recognised as an outlier by the experimenter was excluded from the further analysis 43 44 . Consequently, the number of trials submitted to the analyses per participant was 30.6 ± 3.9 (mean ± s.d.).…”