P025 If a human falls asleep in water do they sleep with half their brain like a dolphin?

Abstract Aims Dolphins sleep one half of their brain at a time presumably to avoid drowning – called unihemispheric slow wave sleep. The Northern Fur Seal has been reported to do this whilst in the water but sleep bihemispherically when it is terrestrial. These observations made us wonder whether unihemispheric slow wave might be an evolutionarily conserved ability in humans that might be revealed if we simply slept in water. Methods We built a waterproof and temperature regulated housing to protect an EEG recorder (Alice PDX, Respironics) from being near a float tank (AKA floatation REST therapy) with very low level light and sound levels and thermoneutral temperature. Float therapy uses a highly concentrated Epsom salt solution making the human body extremely buoyant. Reports of single channel automatically processed EEG being measured in float tanks convinced us we could try to find unihemispheric slow wave in a human sleeping in water. Active EEG placements were recorded at Fp1 and Fp2 both referenced to Fpz on the forehead. Left and right electrooculogram (EOG) was also recorded referenced to Fpz. EEG was scored using Alice G3 Sleepware 3.9.5 (Philips Respironics Pittsburgh, USA) following the scoring manual American academy of sleep medicine. A single male human with previous float tank experience was recorded in the float tank in the morning (1 hour). Results We captured scorable EEG and detected stage 2 sleep characteristic K complexes and sleep spindles. At no point did we detect slow wave sleep or uni-hemispheric sleep. Slow waves around sleep onset are artifactual slow rolling eye movements being detected in these frontal channels. Discussion It is possible to record EEG and score human sleeping in water. We saw no asymmetry in the stage 2 sleep but captured no SWS to compare to see whether humans sleep like dolphins in water.