Ultradian and infradian rhythms

W/in sleep portion of sleep/wake cycle - ultradian rhythm - bio rhythm shorter than 24 hours. 5 stages of sleep.

Follows pattern of REM + NREM sleep - stages 1-4. Cycle repeats itself every 90-100 mins, diff stages having diff durations. Complete cycle - progression of 4 stages NREM before final stage REM sleep, whole cycle starts over again.

Most of what we know comes from EEG - enters deep sleep, brainwaves slow, breathing + heart rate decrease. 5th stage, EEG pattern resembles awake person, stage most dreaming occurs

Kleitman (1969) - referred to 90 min cycle during sleep as basic rest activity cycle. Also suggested 90 min UR continues during day. Diff is - during day, rather than stages of sleep, move progressively from state of altertness into state of physiological fatigue approx every 90 mins. 

Research suggests mind can focus for 90 mins, towards end of 90 mins runs out of resources -> loss of concentration, fatigue + hunger. 

Op of BRAC in wakefulness not as obvious as sleep, but everyday obs evidence of existence eg 10:30 break allows workers to divide 9am-12 into 2 sessions.

Bio rhythm duration longer than 24 hours.

Grouping of 7 days into week common in most areas, obvious diffs in human behaviour conform to weekly cycle. Eg testosterone levels elevated at weekends, young couples report more sexual activity at weekends.

Variations in length, some 23 days, some 36. Regulated by hormones, either promote ovulation or stimulate uterus for fertilisation. Ov occurs halfway through menstrual cycle, oestrogen levels peak, usually lasts 16 -32 hours. After ov phase, progesterone levels increase in prep for poss implantation of embryo into uterus.

Most animals, related to seasons - humans, calendar year happens regardless of chnages in temp.

Research suggests seasonal variation in mood, especially women, some becoming severely depressed in winter - seasonal affective disorder (SAD). Winter associated w/ increase in heart attacks, varies seasonally, peaks in winter.

Ericsson et al (2006) - group elite violinist, found practice sessions usually limited to no more than 90 mins, practice systematically distributed during day in 90 min segments. BRAC cycle.

Menstrual cycle influences mate choice - Penton-Voak et al (1999) - diff prefs at diff stages. Women pref for 'slightly feminised' male faces when picking partner for LT relationship. In ov phase, pref for more masc faces - 'good genes' in short liasons.

Individual diffs in sleep stages - diffs in sleep patterns usually attributed to diffs in non-bio factors. Tucker et al (2007) - bio determined, genetic in origin. 11 days + nights, lab environment. Assessed sleep duration, time to fall asleep + amount of time in each sleep stage - diffs bio.

Menstrual cycle - also controlled by exogenous cues eg synching periods.

Belief in lunar rhythms - eg many midwives believe more babies born during full moon than new moon.