Biological rhythms, Sleep and Dreaming

. Infradian Rhythms are longer than 24-hours . Human menstrual cycle best known (egg released into ovary every 28 days) . McClintock identified synchronisation of menstruation . Synchronisation among 135 femal friends caused by phremones . McClintock and Stern carried out 10-year longitudinal study on women between ages of 20-35 with a history of irregular ovulation . Researchers gathered pheremone samples from 9 pp's arm pits at certain points in their cycle and exposed the reamining 20 women to the phremones by wiping them under their noses . 68% of women responded to the pheremones with their menstrual cycles being lengthened or shortened . Seasonal affective disorder can be regarded as an infradian rhythm as it occurs annually in the winter months . SAD is disorder which shows seasonal changes in mood or behaviour . Still unclear but believed that lack of light in winter months means too much meletonin is produced . Exposure to bright light can slve this as shown by Terman . 85 pp's with SAD recieved daily 30-minute exposures to bright light