Complex Relationship Between Critical Flicker Fusion Frequency and Established Cognitive Tests Unveiled by Hyperbaric Exposure

Critical flicker fusion frequency (CFFF) has been proposed as a rapid marker of central nervous system arousal state, but its relationship to cognitive performance under hyperbaric stress remains unclear. Forty healthy adults (20 women; age 19-46 years) underwent three hyperbaric exposures at 4 ATA (equivalent to 30 m seawater depth) while breathing air, heliox, and trimix in randomized order. CFFF and cognitive performance (Simon task, Digit Span, Corsi Block-Tapping) were assessed before compression, at 4 ATA, and after decompression. Both CFFF and reaction times increased modestly at 4 ATA across all breathing gases (3-5% elevation, p < 0.05). Following decompression, however, these measures showed divergent recovery patterns: CFFF normalized completely after heliox and trimix, but remained partially elevated after air breathing. In contrast, reaction times improved substantially after decompression (10-15% faster than baseline) regardless of breathing gas, reflecting practice effects. Weak correlations emerged between specific CFFF components and executive cognitive measures, while memory performance remained stable throughout all conditions. CFFF and cognitive performance exhibit some parallel increases under hyperbaric stress but most likely capture largely independent aspects of neural function. Breathing gas composition selectively influences CFFF recovery dynamics, with nitrogen producing prolonged neural effects relevant for assessing post-dive cognitive readiness.