Ultradian Rhythms.

Ultradian rhythms are those which last less than 24 hours.

There are many ultradian cycles, the majority of these occuring without us noticing them, such as temperature regulation, hormone secretion and heart rate.

Ultradian Rhythms are very largely under endogenous control, although everyday observation clearly indicates exogenous influence.

In this study pack we will look at;

• REM/NREM sleep.
• The basic rest activity cycle (BRAC)
• Neurochemical activity.
• Urine flow.

Sleep has its own identifiable rhythm. The two basic sub-phases of sleep which make up this rhythm are;

1. REM (Rapid eye movement.)        2. NREM (Non-Rapid eye movement.)

• When we first go to sleep we enter the first four stages of REM sleep.
•  Stages 3 and 4 of NREM together are known as slow wave sleep (SWS).
• After about 20 minutes in SWS we enter REM sleep.
• For the remainder of the night, sleep shifts between these two phases of sleep in an appropriate 90 minute cycle.
• As the nights sleep progresses SWS gets shorter, with the REM stage getting longer but still maintaining the 90 minute cycle, so that the later cycle might consist of 30 to 40 minutes of REM and 50 to 60 minutes of SWS.

The regularity of the 90 minute cycle suggests that there must be a brain mechanism alternately causing REM and NREM.

Jouvet (1972)

•  destroyed an area just below the locus coerulus in the brain stem of cats and found that this permanently destroyed their REM sleep.

Webster and Jones (1988)

• Supports the theory that chloinergic cells are essential for REM sleep.
• They show that the loss of REM sleep is proportionate to the number of cells destroyed.

Hobson et al (1975)

•  Said that the REM/NREM ultradian cycle is thought to be generated by the contrasting activities of REM on and REM off cells in the pontine reticular formation of the brain stem.

Kleitman (1961)

• Proposed a basic rest activity cycle (BRAC).
• This theory assumes taht the 90 minute REM/NREM cycle that occurs during sleep continues over the 24 hours of the day and includes arousal and behavioural activity of the waking person.
• In effect the REM/NREM cycle is the nocturnal fragment of a 24 hour BRAC.

SUPPORT COMES FROM... Kales and tan (1969)

• found greater secretions during REM than NREM sleep.

Friedman and Fischer (1967)

• found 90-120 minute cycles of 'oral' waking behaviour such as eating, drinking etc.

Haitt and Kripke (1975)

•  inflated balloons in the stomachs of fasting participants in order to measure gastric contractions.
• found a clear ultradian rhythm over an eight our period of measurement.
• 

Grivel and Ruckebusch (1967)

• Found 60-90 minute gastric contraction rhythms in dogs sheep and rabbits, all of which have REM/NREM cycles of 20-30 minutes.
• 

HOWEVER...research has failed to find a relationship between REM/NREM cycles and gastric contractions. It seems that there was an error in earlier studies as they wrongly associated a gastric ultradian cycle with REM/NREM sleep, and thus a BRAC cycle.

Support; Kripke and Sonnenschien (1978)

• found 90-120 minute cycles in vivid daydreaming.

Lavie (1979)

• found evidence for fluctuations in alertness and people's ability to fall asleep.
•  Pp's attempting to fall asleep every 20 minutes showed a rhythm of stage 1 sleep approximately every 100 minutes.
• 

HOWEVER... Okudaira et al (1983)

• Could not find any evidence of 90-100 minute rhythms in their study.
• They concluded that whilst there may be cycles in other apects of functioning, one does not exist in levels of bodily activity.

Neubauer and Freudenthaler (1994)

• Searched for an ultradian rhythm in human cognitive performance.
• They gave their 60 pp's a basic cognitive task every ten minutes for 9 hours.
• They could not find any evidence for a 90 minute cycle in any variables they measured.
• They suggest that the BRAC may emerge both from analysis and date because of the statistical methods used.
• 

So...

• Whilst there is evidence to support ultradian cycles in the body during waking, no support has emerged for the notion that they have a common BRAC mechanism.

Kennedy et al (2002)

• measured levels of tryptophan (TRP) and 5-hydroxy indoleacetic (5-HIAA) in the cerebrospinal fluid (CSF) of 12 healthy volunteers.
• They found evidence for ultradian rhythms in the concentrations of both TRP and 5-HIAA.

Salomon et al (2005)

• Investigated neurochemical ultradian rhythms in people with depression
• They took CSFsamples from 15 depressed patients at 10 minute intervals for 24 hours before and after anti-pressent treatment.
• A change in ultradian rhythm cycle length of 5-HIAA was obsevered following treatment, suggested that abnormal ultradian rhythms are part of the general pathophysiology of depression.

Mandell et al (1966)

• Cathersised 7 male particpants and measured the urine flow over 11 nights. Because of the catherter the urine would not be held in the bladder and would continuously pass into a measuring container.
• Within 2 minutes of the onset of REM sleep the quantity of urine decreased.
• At the end of the REM phase urine flow increased again.
• They suggest that these changes were a result of changes in renal function associated with REM sleep, in particular, secretion of anti-dieretic hormone (ADH) occuring rhythmically with REM sleep onset and offset.

HOWEVER...It is possible that urine flow was alterted by changes to bladder tone and compression to the catherter tube caused by penile erectin, which occurs during REM sleep.

HOWEVER...Rubin et al (1975)

• could find no evidence of a correlation between ADH and sleep cycles.

Lavie and Kripke (1977)

• Avoiding the use of a catheter, they asked their pp's to drink a constant set amount of liquid over a ten hour period.
• Pp's we asked to urinate as much as possible every ten minutes.
• They reported prominent ultradian rhythm of 80 to 133 minutes in the urine flow of their pp's concluding that this was due to a rhythmic secretion of ADH.