Infradian Rhythms.

Indradian rhythms are rhythms that last longer than 24 hours, for example, the menstrual cycles and hibernation etc.

There are many variations in such bioloigical rhythms. For Example;

• some occur on a monthly cycle
• whilst others appear to follow tidal rhythms.

Many behaviours appear to have a much longer rhythm, cycling on seasonal or annual basis. These are offen reffered to as circannual rhythms.

An example of research into this comes from; Pengelley et al (1978)

• kept squirrels under constant 24 hour light and 34degree temperature for 3 years.
• they found that the animals body weight and food consumption rhythm followed a circannual cycle independant of temperature and light.

• A number of animals that experience a combination of long cold winters and reduced food availibility go through periods of reduced feeding and activity, a sort of 'deep sleep', called hibernation.
• Hibernation involves significant changes to bodily functions - for example, kidney function, metabolism, heart rate and circulation

Dawe and Spurrier (1968)

• transfused blood from hibernating ground squirrels into active ones and noted that within 48 hours these active squirrels began hibernating.

Although it hasn't been isolated or analysed, it seems that there is a chemical in the blood of some animals which induces hibernation. This has been called 'hibernation induction trigger' or HIT.

One idea is that this substance becomes active when triggered by zeitgebers, (light, short days etc.)

Myers et al (1981)

• Injected Macaque monkeys, directly into the brain which injections of a substance that had been derived from the blood plasma of hibernating 13-lined squirrels.
• They found that for up to 36 hours afterwards the monkeys exhibited reductions in appetite, heartrate and temperature (typical signs of hibernation.)
• They also found that plasma from non-hibernating squirrels had no observable effects of the monkeys.

It has been suggested that HIT acts like an opiate to supress the activity of systems in the central nervouse system.

HOWEVER...some researchers have failed to find evidence of effects similar to those of HIT, in other animals.

Wang et al (1988)

• compared the effects of summer plasma and hibernating plasma derived from Richardsons ground squirrels on the summer hibernation behaviour of both Richardson's and 13-lined ground squirrels.
• They found that whilst 13 lined fround squirrels readily entered hibernation, the type of injections they recieved (whether plasma, warm saline, or even sham injection) had no effect on either the length or quality of hibernation.
• None of the richardson's ground squirrels entered hibernation.
• This study both casts doubt on the existence of blood-bourne 'trigger' substances and suggests that responses to such chemicals may only apply to specific species.

Kondo et al (2006)

• identified another hormone called HP20c, which is found in increases levels in the brains of chipmunks during hibernation.
• They kept chipmunks in a controlled environment of constant temperature and regular 24 hour cycles of day and night.
• They found that levels of HP20c continued to fluctuate on a seasonal basis, suggesting that they were under circannual endogenous control.
• Also, chipmunks that were unable to increase their levels of HP20c were also unable to lower body temperature.

The researchers suggest that this hormone is a key regulator of hibernation, although so far it has not been found in other hibernating animals.

Some people experience annual episodes of depression which seem to occur on a seasonal basis, with the prolem worse in winter and lessening or dissapearing entirley in the summer.

• This disorder, known as Seasonal affective disorder, is relatively common being estimated to afect 6%, or 11 million people in the united states.
• However, it is not equally ditrubted, as more people in nortern states suffer with the disorder than those in the south.
•  The important factor underlying this despersion appears to be the decreased amount of daylight in northern latitudes during the winter months compared by the south.

Sufferers of SAD have a number of circadian abnormalities, including sleep disturbance, increases in core body temperature, and disturbances in cortisol and melatonin secretion.

Eastman et al (1998)

• treated SAD patiented either with bright light (6000LUX) or a placebo.
• They found that those treated with the bright light were more likely to respond with a partial or full remission of symptoms.

HOWEVER...Postolache et al (1998)

• said that treatment with artificial light does not produce as complete a remission of symptoms as occurs during normal summer time.
• Despite being given light treatment at least equivilant to that administered in other clinical trial, patients scored higher on measures of depression after light therapy in winter that during the following summer.
• This may due to a number of factors associated with the quality of light, such as intensity, photoperiod and amount of UV radiation.

Patients with SAD appear to have circadian rthythms which are phase-delayed relative to the light dark cyle, and this may be the principal cause of the disorder.

Lewey et al (1998)

• suggested that treating patients with a phase advance of light period (ie. producing a backward shift in the circadian clock by giving patients more morning bright light) may be more effective that a phase delay of light, (producing a forward shift in the circadian clock with evening bright light.)

The menstrual cycle is the clearest nfradian rhythm in human behaviour. It is a series of physical and hormonal changes that prepare a woman's body for pregnancy.

The average menstrual cycle is 28 days from the start of one to the start of the next, althought it can range from 21 days to 35 days.

It is a widespread believe that women who spend more time with each other will synchronise there menstrual cycles.

Arden et al (1999)

• reported that 80% of women in their study believed that synchrony exists.

• Studied 135 women ages 17-22 living in all female university hallsof residence.
• They were asked to recall previous menstrualperiods over the last year, how much time they spent each week in male company, and how much time they had spent with the females they had considered to be their best friends.
• McClintock found that the menstrual cycles of women who spent extended time together tended to synchronise.

This is SUPPORTED by...

Weller and Weller (1993)

• who also suggest that menstrual synchrony is affected not only by proximity by by the closeness of the relationship between the two women.
• They found a significant degree of synchronancy between mothers and daughters residing in the same home.

The first study that directly investigated the influence of pheromones on the menstrual cycle was conducted by Russel et al (1980);

• They wanted to know if olfactory cues from one woman could influence the timing of menstrual onset of another.
• The collected odour by placing cotton pads in the armpits of donors for 24 hours.
• This cotton pad was now rubbed onto the upper lip ofthe pp's, who were told not to was their faces for six hours. This happened three times a week for six months.
• They report that pp's shifted their menstrual cycles significantly, to resemble the donor's monthly cycle.

Jacob et al (2004)

• found that the menstrual cycle length of pp's could be influenced by exposure to pads odourised in ther nursing brassieres of breastfeeding donors.

HOWEVER...

Wilson (1992)

• says that claims of apparent synchrony are in fact a result of the research method and techniques used, rather than an accurate observation of menstrual behaviour.
• He points out major methodological problems with the research - he believes the studies tend to observe cycles over too short a time and tends to exclude data from pp's who 'don't fit'.
• Wilson also argues that apparent increases in schnrony are due to errors in calculating menstrual onset.

Schank (2000)

• points out that research like this also assumes that women basically have the same stable cycle length, whereas in reality it varies considerably, both within and between females.

Many studies directly contradict the theory of menstrual synchrony.

Yang and Schank (2006)

• Looked at occurance of menstrual cycles in 186 Chinese women living in university accomodation over the course of one year
• Avoiding the methodological errors of previous research they found no evidence beyond the chance lebel that women synchronise their cycles.
• They suggest that the women's perception of synchrony is due to the fact that cycle variability will inevitably lead to repeated cycle meetings, giving the impression of synchrony where none exists.

Ravizza and Ray (1980)

• found that a submissive hamster of a a pair would synchronise it's oestrous cycle to the rhythm of the dominant one.

However, efforts to replicate these findings failed. And no other studies since have reported cycle synchronation in mammals.

Gatterman et al (2002)

• Kept female golden hamsters living either in groups, or seperatley but connected by cages. These hamsters are known for their stability of their cycles.
• They found no evidence of synchrony in either group of hamsters.

• It has been suggested that makes with multiple wives would be more able to detect pheromone signals of fertility, thereby increasing the probability of conception in the co-wives.
• It has also been suggested that menstrual sychrony increases infant survival chances, since new mothers would also have synchronised lactation. They would be able to feed eachothers offspring and, if a mother died, remaining babies could still be nursed.
•  

However, there is a lack of any firm evidence for these theories.

Another theory from Gatterman et al (2002);

• suggests that asynchronous cycles could be adaptive in some animals.