DISORDERS OF THE SLEEP-WAKE CYCLE IN ADULTS

Adults have an intrinsic body clock which regulates a complex series o f rhythms including sleep and wakefulness, fatigue and cognitive abili ty. This endogenous clock naturally runs more slowly than the solar da y and is entrained to a 24-h rhythm primarily by the alternation of Li ght and darkness. Jet lag, shift-work sleep disorder, and some of the chronic insomnias are caused by a temporal discrepancy of the body clo ck relative to the surrounding environment and social network. The und erlying mechanisms and general management are described. Both bright l ight and melatonin therapy have potential in the management of these d isorders. Traditionally, bright Light therapy has been used to allevia te the depression associated with seasonal affective disorder. Melaton in has received much ill-formed publicity, it being claimed that it is a panacea and an 'anti-ageing' treatment. Both of these treatment app roaches are reviewed.