Previous studies demonstrated that (a) mice preferentially sleep durin
g li
ght hours and they are preferentially awake durin
g dark hours; (b) mice have fra
gmented sleep. Despite multiple investi
gations involvin
g sleep-wake transitions in mice, the exact patterns of sleep-wake alternations are not known. Here we studied sleep-wake pattern distribution in 5 youn
g adult C57BL/6 mice over 5 days usin
g continuous LFP and EMG recordin
gs with a resolution of 5 s. The states were automatically detected based on LFP delta power, theta power and EMG power. We found that daily distribution of states of vi
gilance in mice was: 12 h of wake, 10.2 h of slow-wave sleep and 1.8 h of REM and it was characterized by several hundred of transitions between different states of vi
gilance. The majority of detected states lasted less than 40 s. The fra
gmentation of states of vi
gilance was hi
gher in the li
ght part of the day and lower in first several hours of the dark part of the day when wake episodes were lon
ger and REM sleep was almost absent. The most stable state of vi
gilance (lon
gest stable se
gments) in mice was slow-wave sleep. The main EEG events that contribute to the delta power are slow waves. The existin
g methods of automatic slow wave detection were not sufficiently robust for their effective automatic reco
gnition in non-anaesthetized mice. We developed a new method for slow wave detection based on neural network pattern reco
gnition and classification, which allowed to retrieve various features of the slow waves in lar
ge amounts of data. As expected, we found many slow waves durin
g slow-wave sleep. Surprisin
gly, isolated slow waves were also present durin
g wake and occasionally durin
g REM sleep. Both delta power and number of slow waves per second were the hi
ghest at the be
ginnin
g of the li
ght cycle, then
gradually decreased to the end of the li
ght cycle and reached their minimum in first 3–4 h of the dark cycle. Even thou
gh the slow-wave sleep episodes were shorter and occurred less often durin
g dark part of the day, they had hi
gher density in comparison to slow-wave sleep durin
g the li
ght part of the day. We conclude that the results of studies of normal sleep-wake cycle in C57BL/6 mice cannot be directly translated to human research or clinic.
Supported by CIHR and NSERC.