Critical Flicker Fusion Frequency: A Marker of Cerebral Arousal During Modified Gravitational Conditions Related to Parabolic Flights

Abstract

In situ evaluation of human brain performance and arousal remains challenging during operational circumstances, hence the need for a rapid, reliable and reproducible tool. Here we hypothesized that the Critical flicker fusion frequency (CFFF) reflecting/requiring visual integration, visuo-motor skills and decision-taking process might be a powerful, fast and simple tool in modified gravity environments. Therefore 11 male healthy volunteers were assessed for higher cognitive functions with CFFF during parabolic flights. They were assessed at different time points: upon arrival to the base, 30 min after subcutaneous scopolamine administration, before parabolas, during hypergravity and microgravity at break time (between the 16th and the 17th parabola), on the return flight and on the ground after landing. First, a stable, and consistent measurement of CFFF could be obtained within 12 s. Second, under modified gravitational conditions, the perceptual ability of participants is significantly modified. Compared to the baseline, evolution is characterized by a significant increase of CFFF when in microgravity (0g: 106.9 ± 5.5%), and a significant decrease of CFFF while in hypergravity (2g: 94.5 ± 3.8%). Other time-points were not statistically different from the baseline value. Although the underlying mechanism is still debated, we suggest that the CFFF test is a global marker of cerebral arousal as the result of visuo-motor and decision taking testing based on a simple visual stimulus with an uncomplicated set up that could be used under various environmental conditions. The authors express an opinion that it would be advisable to introduce CFFF measurement during spaceflights as it allows individual longitudinal assessment of individual ability even under conditions of incomplete physiological compensation, as shown here during parabolic flights.

Variation of Cognitive Function During a Short Stay at Hypobaric Hypoxia Chamber (Altitude: 3842 M)

“…Arousal is triggered by the stimulation of the ascending reticular substance (Jang et al, 2016) and it could be interrogated by CFFF. Furthermore, the decrease in CFFF could be due to decreased cerebral blood flow index Some similar results have been reported during acute orthostatic stimulations altering cerebral blood flow (Balestra et al, 2018). Similar results have been shown when using Cerebral Near Infrared Spectroscopy to assess brain’s oxygenation (Sakudo, 2016).…”

“…When the subject saw a change in LED light from flicker to fusion, the subject acknowledged it to the investigator (through a sign without leaving sight of the LED) and the test was stopped. This noninvasive test has been validated to measure awareness (Hemelryck et al, 2013; Balestra et al, 2018; Rocco et al, 2019), mental fatigue (Ma et al, 2014), or executive dysfunction (Mewborn et al, 2015). It has already been demonstrated that CFFF could follow the recovery of cognitive function after propofol sedation earlier than psychometric testing (Sharma et al, 2011).…”

Field study of anthropomorphic and muscle performance changes among elite skippers following a transoceanic race

“…Our results confirmed an increased perceived fatigue both on subjective (VAS) and objective assessment (CFFF). Indeed, CFFF has been used with success in several models of extreme exposure such as divers [28,30], pilots [31] or parabonauts [32] and has been seen as a global index of cerebral arousal, however with an easier set-up. Since, it was demonstrated on short races that it was possible to minimise anxiety and perceived fatigue with adequate sleep to optimise performance and efficiency [8], it implies that an improved arousal may be a surrogate of an improved performance.…”

The effect of acute, moderate intensity indoor cycling on the temporal resolution of human vision system, measured by critical fusion frequency

“…There are several mechanisms operating on a hormonal and vascular level, which have been suggested for exercise-related improvement in the processing of visual stimuli, such as neurogenesis and synaptogenesis through increased production of brain-derived neurotrophic factor, augmented neurotransmitter levels and effectiveness, peripheral mechanisms, including the release and transport of circulating catecholamines, an increase in cerebral blood flow, and stimulation of the neuroendocrine system by the modulation of the sympathoadrenal system and hypothalamic-pituitary-adrenal axis (Al-Nimer & Al-Kurashy, 2007;Balestra et al, 2018;Hanson et al, 2018;Simonson & Brozek, 1952).…”