Fig. 3. Functional plasticity of glycogen metabolism during sleep–wake cycle. Glycogen synthase activity is induced by sleep deprivation and returns to normal levels after 3 h recovery. ZT6, undisturbed animals sacrificed 6 h after light onset; SD6, animals sacrificed at the end of a 6 h sleep deprivation period; ZT9, undisturbed animals sacrificed 9 h after light onset; SR3, sleep deprived animals sacrificed after 3 h of sleep recovery. Asterisks, P<0.01.