Sleep-waking rhythm altered by 2-hour light phase access to food in the rat

The effects of 2-h restricted feeding (RF, 10.00-12.00 h) on sleep rhythms were examined in 9 male rats on a 12:12 h LD cycle (L 08.00-20.00 h). During the third week of RF, sleep amounts showed a striking reduction during a 4-h period (08.00-12.00 h), and LD differences in SWS and PS amounts were markedly reduced. Hourly sleep amounts showed a bimodal distribution during a 24-h day. Analyses of periodicity of SWS and PS occurrences revealed a dominant 12-h periodicity and a relative diminution of the 24-h one. The appearance of a 12-h rhythm of sleep may be due to an interaction of the two zeitgebers (LD cycles and restricted feeding) and possibly to the timing of RF.