Infradian Rhythms

Summary

This lesson delves into infradian rhythms, specifically focusing on the menstrual cycle and Seasonal Affective Disorder (SAD). It explains how internal factors like hormones and external influences such as pheromones and light affect these cycles. The role of synchronization in the menstrual cycle is discussed, along with the evolutionary benefits and potential confounding factors. SAD is linked to melatonin overproduction and light exposure, with phototherapy suggested as a treatment. The lesson highlights the complexity of biological rhythms and their interaction with both internal and external factors.

Takeaways

• 📚 The lesson focuses on infradian rhythms, which are biological rhythms longer than a day, including the menstrual cycle and Seasonal Affective Disorder (SAD).
• 🌊 Infradain rhythms are distinguished from circadian and ultradian rhythms by their less frequent periodic cycles.
• 🔬 The menstrual cycle is controlled by hormones like estrogen and progesterone, which are internal factors, and can be influenced by external factors such as synchronization with other women's cycles.
• 🌡️ Synchronization of the menstrual cycle can be influenced by pheromones, chemical signals released into the environment that can affect others' internal mechanisms.
• 🧬 Martha McClintock's study showed a correlation between close living conditions and menstrual cycle synchronization among women in an all-female dormitory.
• 🤔 The role of pheromones as internal or external factors in biological rhythms is a point of analysis, given their release into the environment but biological origin.
• 🕰️ A study involving a woman in a cave without natural light showed that the absence of light can affect the menstrual cycle, indicating light as an exogenous factor.
• 🌞 The evolutionary value of menstrual cycle synchronization may include shared childcare and fair competition for mates, though this idea is debated.
• 🌨️ Seasonal Affective Disorder is a type of depression with symptoms like low energy and social withdrawal, linked to reduced daylight during winter.
• 🌞 Endogenous factors in SAD include overproduction of melatonin and underproduction of serotonin, while exogenous factors are the absence of light.
• ✨ Phototherapy, or light exposure, has been effective in treating SAD, suggesting a strong link between light and the disorder's symptoms.

Q & A

What are infradian rhythms in the context of biopsychology?

Infradian rhythms are biological rhythms that occur over a period longer than a day, as opposed to circadian and ultradian rhythms which have more frequent cycles.

What is an example of an infradian rhythm mentioned in the script?

The menstrual cycle is given as an example of an infradian rhythm in the script.

What is Seasonal Affective Disorder (SAD)?

Seasonal Affective Disorder is a type of depression that occurs during the winter months, characterized by symptoms such as low energy, hypersomnia, weight gain, and social withdrawal.

How do infradian rhythms differ from circadian and ultradian rhythms?

Infradian rhythms have a less frequent regularity compared to circadian rhythms, which include the sleep-wake cycle and hormonal fluctuations, and ultradian rhythms, which include stages of sleep like REM and non-REM sleep.

What role do estrogen and progesterone play in the menstrual cycle?

Estrogen causes the ovary to develop an egg which is released during ovulation, while progesterone helps the womb lining to thicken in preparation for pregnancy. If the egg isn't fertilized, the lining is disposed of, resulting in the menstrual cycle.

What is synchronization in the context of the menstrual cycle?

Synchronization refers to the phenomenon where being around other people on their menstrual cycle can influence one's own menstrual cycle, possibly due to the influence of pheromones.

What is the evolutionary value of menstrual cycle synchronization according to the script?

The evolutionary value of synchronization could be that if women menstruate and ovulate at the same time, it increases the likelihood of them getting pregnant simultaneously, which might be beneficial for sharing the care of babies in a group or tribe setting.

What is phototherapy and how is it related to Seasonal Affective Disorder?

Phototherapy is the use of light exposure as a treatment for conditions like Seasonal Affective Disorder. It is based on the idea that the symptoms of SAD are related to the reduced light levels during winter months.

What are the potential confounding variables in the study of Seasonal Affective Disorder?

Potential confounding variables include increased bills for artificial light and heating, the psychological impact of Christmas and the holiday season, and lifestyle changes such as reduced outdoor activity due to cold and darkness.

Why might not everyone exposed to reduced daylight develop Seasonal Affective Disorder?

Not everyone develops Seasonal Affective Disorder because there may be genetic predispositions and underlying mental health issues that make some individuals more susceptible to the condition than others.

How does the study of pheromones relate to the synchronization of the menstrual cycle?

The study of pheromones is relevant to menstrual cycle synchronization because these chemical signals, released into the environment, can influence the internal mechanisms of others, potentially affecting their menstrual cycles.

Outlines

00:00

🌓 Infra-Daily Rhythms and Menstrual Cycle

This paragraph introduces the topic of infradian rhythms from the AQA syllabus for biopsychology, focusing on biological rhythms that exceed a day in duration, such as the menstrual cycle. It explains the distinction between infradian, circadian, and ultradian rhythms, and suggests a strategy for answering extended questions on this topic. The menstrual cycle is explored in terms of its endogenous factors, like estrogen and progesterone, and exogenous factors, such as social synchronization influenced by pheromones. The paragraph also touches on the evaluation of these rhythms, including the role of internal validity in research methods.

05:02

🌞 Synchronization and Seasonal Affective Disorder

This section delves into the concept of synchronization of biological rhythms, particularly the menstrual cycle, and its potential evolutionary value. It discusses the possibility of women menstruating and ovulating in sync to increase the chances of pregnancy and the sharing of childcare within a group. However, it also presents counterarguments to this theory. The role of pheromones in synchronization is supported by a study involving cotton wool pads soaked in sweat, which influenced the menstrual cycles of other participants. The paragraph also introduces Seasonal Affective Disorder (SAD), a type of depression occurring in winter due to low light levels, and its symptoms like low energy and social withdrawal. The endogenous factors of SAD are the overproduction of melatonin and the underproduction of serotonin, while the exogenous factor is the lack of light.

10:05

🌡️ Seasonal Affective Disorder and Light Therapy

The final paragraph discusses Seasonal Affective Disorder in more depth, focusing on the hormonal imbalances caused by increased melatonin production during winter months, which may lead to a decrease in serotonin and other hormones affecting mood and appetite. Empirical evidence supporting the link between high melatonin levels and SAD is presented, along with the effectiveness of phototherapy in treating the disorder. The paragraph also considers the role of confounding variables such as increased bills, the festive season's impact on loneliness, and reduced outdoor activity during winter, which may contribute to SAD. It concludes by noting that not everyone exposed to winter conditions develops SAD, suggesting a genetic predisposition and other mental health factors that may influence its development.

Keywords

💡Biological Rhythms

Biological rhythms are the periodic cycles that organisms display as part of their natural physiology. In the context of the video, these rhythms are central to understanding how our bodies operate on different cycles, such as the sleep-wake cycle and hormonal fluctuations. The script discusses infradian rhythms, which are cycles that take longer than a day, as the main focus of the lesson.

💡Infradian Rhythms

Infradian rhythms are a type of biological rhythm that occurs at intervals longer than a day. The video script uses the menstrual cycle as an example of an infradian rhythm, emphasizing that these rhythms are less frequent than circadian and ultradian rhythms. The concept is integral to the lesson as it sets the stage for a deeper exploration of specific biological cycles.

💡Menstrual Cycle

The menstrual cycle is a biological process that occurs in females, involving hormonal changes and the reproductive system. It is highlighted in the script as an example of an infradian rhythm, with a focus on how it is influenced by both internal hormonal factors like estrogen and progesterone, and external factors such as synchronization with other women's cycles.

💡Seasonal Affective Disorder (SAD)

Seasonal Affective Disorder is a type of depression that follows a seasonal pattern, typically occurring during the winter months. The script discusses SAD as another example of an infradian rhythm, linking it to the reduced levels of light and its impact on melatonin and serotonin production, which in turn affects mood and behavior.

💡Circadian Rhythms

Circadian rhythms are the body's internal clock, approximately 24-hour cycles that regulate sleep, wakefulness, and other physiological processes. The script briefly mentions circadian rhythms in contrast to infradian rhythms, using the sleep-wake cycle and body temperature regulation as examples.

💡Ultradian Rhythms

Ultradian rhythms are cycles that occur more frequently than once every 24 hours, such as the stages of sleep. The script touches upon ultradian rhythms to provide a complete picture of the different types of biological rhythms, with the distinction between REM and non-REM sleep as an example.

💡Estrogen and Progesterone

Estrogen and progesterone are hormones that play a crucial role in the menstrual cycle. The script explains that estrogen triggers the development of an egg, while progesterone helps thicken the uterine lining in preparation for pregnancy. These hormones are key to understanding the internal factors dictating the menstrual cycle.

💡Synchronization

Synchronization refers to the phenomenon where the menstrual cycles of women living in close proximity tend to align over time. The script cites Martha McClintock's study on women in all-female university dorms to illustrate the influence of pheromones and social factors on the menstrual cycle.

💡Pheromones

Pheromones are chemical signals released by an individual that can affect the behavior or physiology of others. In the script, pheromones are discussed as a potential external factor influencing the synchronization of menstrual cycles, highlighting the complex interplay between internal and external biological influences.

💡Evolutionary Value

The concept of evolutionary value in the script refers to the potential survival advantages that certain biological traits or behaviors may have provided our ancestors. The script suggests that the synchronization of menstrual cycles could have had evolutionary benefits, such as more efficient childcare and fairer competition for mates.

💡Phototherapy

Phototherapy, as discussed in the script, is the use of light exposure as a treatment for conditions like Seasonal Affective Disorder. It is an application of the understanding of how light, or the lack thereof, affects mood and physiological processes, providing a practical approach to managing SAD symptoms.

Highlights

Biological rhythms are periodic cycles that occur regularly, with infradian rhythms taking longer than a day, such as the menstrual cycle.

Infradian rhythms are distinguished from circadian and ultradian rhythms by their less frequent regularity.

The menstrual cycle is controlled mainly by hormones estrogen and progesterone, which are endogenous factors.

Synchronization of the menstrual cycle can be influenced by external factors such as pheromones from other women.

Martha McClintock's study found a correlation between exposure to other women and menstrual cycle synchronization.

Pheromones, released through sweat and body odor, can send signals that influence others' internal mechanisms.

The role of pheromones in synchronization raises questions about whether they are considered internal or external factors.

Isolation studies show that the absence of natural light can shorten the menstrual cycle, indicating light as an exogenous factor.

Synchronization of menstrual cycles may have evolutionary value, such as shared care of babies and fair competition for mates.

Shanks argues against the idea that competition is the basis of synchronization, suggesting women tend to 'tend and befriend' rather than compete.

A study involving cotton wool and pheromones found synchronization effects, supporting the role of pheromones in cycle synchronization.

Mathematical chances suggest that women may naturally synchronize menstrual cycles over several cycles, independent of pheromones.

Seasonal Affective Disorder (SAD) is a type of depression with symptoms similar to regular depression but occurring only in winter months.

SAD is linked to low light levels during winter, affecting melatonin and serotonin production.

Phototherapy, or light exposure, has been effective in treating SAD, suggesting the importance of light as an exogenous factor.

Not everyone exposed to reduced daylight develops SAD, indicating a possible genetic predisposition or other underlying factors.

Confounding variables such as higher bills, holiday stress, and reduced outdoor activity may exacerbate winter depression but are difficult to study in isolation.

Transcripts

so this is another lesson for

biopsychology from the AQA syllabus

psychology paper 2 uh we're looking at

biological rhythms today and we're going

to specifically focus on infradian

rhythms just a reminder infradian

rhythms are biological rhythms that take

longer than a day and an example here in

the glossery is the menstrual cycle

we'll also be looking at Seasonal

effective disorder as all other

biological rhythms they're periodic

cycles that happen regularly only that

the regularity of these ones is less

frequent than Cadian and ultradian

rhythms so just a reminder for Cadian

rhythms you can look at for example the

sleep wake cycle body temperature and

hormonal

fluctuations uh for ultradian rhythms

you will look at stages of sleep

specifically the distinction between RM

and nonm sleep

and for even Fran rhythms we will look

at today the menstrual cycle and

seasonal effect of

disorder we will start by looking at the

menstrual cycle ao1 and then the

menstrual cycle AO3 and then the do the

same sequence for the Seasonal effective

disorder this is also a good strategy

should you get an extended question on

infradian rhythms you might want to

split it into a1's for menstrual cycle

a3s for menstrual cycle and then then

again for seasonal effectory

Disorder so you might not see this but

as for cadium rhythms you can organize

your ao1 into the role of endogenous

pacemakers and exogenous zeit gers so

you will look to what extent the

menstrual cycle is dictated by internal

factors such as um estrogen and

progesterone and to what extent it's

determined by external factors and we

will see that in this case the external

Factor are other women other people on a

cycle so

synchronization and link to that the

role of pheromones and then when we look

at evaluation remember evaluation AO3 is

evaluation and Analysis so you can

analyze uh synchronization for example

as having evolutionary value you can

also uh look at the methods that are

used to research um the menstrual cycle

and to what extent they have internal

validity and to what extent they have

issues so uh as you might already know

the menstrual cycle is controlled mainly

by the hormones estrogen and pro

progesterone so these are the indous

factors that determine a menstrual cycle

you would want to go into a bit more

detail and say that estrogen causes the

ovary to develop an egg it's uh released

and this is called ovulation and then

progesterone helps the womb lining to

grow thicker ready for pregnancy but if

uh the egg isn't fertilized then it's

disposed so the menstrual cycle is the

result of this

disposal now external factors here are

synchronization it means that being

around other people on their menstrual

cycle uh can

change the cycle of One's Own menstrual

cycle uh Martha mlin Tuk studied this

looking at women that lived in all

female univers dorms and found that

there was a strong positive correlation

between how long people were exposed to

each other so spent time together and

how closely they experienced their

menstrual

cycle so this emphasizes the role of

pheromones pheromones are like our

hormones but released into the outside

world through our sweat our body smell

our skin basically our skin conduct

these pheromones that s send signals to

others about our internal mechanisms and

therefore uh might influence their

internal mechanism so there's definitely

a question here for Ure fre as to where

pheromones are considered internal or

external because they're released into

the outside world so other people's

pheromone can influence us but then

again they're a biological factor so

that's a good an analysis

point and as I said there's uh in terms

of exogenous Z gabes there's isolation

studies like in the Cadian rhythms you

remember cifra so here we've got another

study but this time it's a woman who

spent three months in a cave with uh no

natural light and it was found that her

menstrual cycle shortened and this shows

that light is also an exogenous factor

that might be implicated in the

menstrual cycle so not only pheromones

and exposure to other individuals but

also the presence of our absence of the

light seems to synchronize not only the

sleep wake

cycle so moving on to

AO3 uh we can talk about the

evolutionary value of synchronization if

women are uh menstrating at the same

time they're also ovulating at the same

time meaning there's a highly higher

likelihood of them uh getting pregnant

at the same time and therefore the

children being born at the same time so

if living in a in a group in a tribe

that might make it uh more effective in

terms of sharing uh the care of babies

lactating at the same time Etc also

competition for males is fairer if all

women are either fertile or not fertile

in

sync there are arguments against this as

you can see Shanks argues that it's not

really true that uh for women

competition promotes survival women are

more kind of tend and befriend rather

than fight or flight um spe genders and

therefore the idea that uh that

competition is at the basis of

synchronization doesn't really have a

sound sound

basis there's also research to support

uh

synchronization uh this is a slightly

disgusting stud study where participants

Place coton wool uh under their armpits

without deodorant so the coton W was

impregnated with the sweat and then that

was swiped on the upper Li lip of

another participant and that was to

expose that participant to the

pheromones of uh of the sweating

participant and they did find that uh

through smelling the pheromones of U of

the other participants the ones uh

exposed to the pheromones did seem to

synchronize or that there get closer to

the kind of the donors of the pheromones

so this is supporting evidence in a kind

of standardized control

um study Beyond just looking at young

people that spent time together in dorms

that is yeah more naturalistic more with

high ecological validity but not with a

high control of other extraneous

variables so this seems to substantiate

the role of pheromones in

synchronization now generally speaking

there are the questions about

synchronization the first one is that

mathematically we're women are bound to

synchronize at some po point in the

course of three or four Cycles

especially because the length of stud of

um Cycles is not the same for everyone

so it's based on the flawed assumption

that everybody's cycle is 28 days for

example so there are kind of

mathematical reasons where by

synchronization could happen just by

chance rather than because of exposure

to

pheromones we're Mo moving on now to the

second infradian Rhythm so we're going

to look at the AO ons for Seasonal

effective disorder first of all Seasonal

effective disorder is a specific type of

depression that is similar to depression

in terms of its symptoms however it only

occurs during the winter months and this

seems to be attributed to uh the low

levels of light uh the symptoms include

low energy hypersomnia that means

sleeping too much overing weight gain

and social withdrawal so spending a lot

of time alone at home either sleeping or

eating this is what it

suggests now

for Seasonal effective disorder the

endogenous pacemakers that are involved

are um the prod the over production of

melatonin that results in the

underproduction of Serotonin and the

exogenous light Gaber is the absence of

light and therefore in the winter months

we know that the days are shorter in

terms of A3 we don't have a lot we have

phototherapy that is PR practical

application of our knowledge into the

reasons why sad might um occur and how

we can treat

it so melatonin uh is a hormone the

endocrine system is the system of glands

that secrete hormones so if there's an

over production of melatonin there will

be a strain in the pineal gland that

might result in an underproduction of

other hormones within the endocrine

system in this case the hormones that

might be influenced are um the thyroid

hormone serotonin and adrenaline so it

makes sense to think that if you're

producing loads of melatonin because

it's nearly always dark then you will be

producing less of that mood regulating

hormone serotonin uh T the thyroid

meaning that you might feel hungry when

you don't need food and the lack of

adrenaline might not motivate you to go

out so it does link to all of the

symptoms that we described

[Music]

earlier sad patients have consistently

higher daytime melatonin levels so there

is empirical evidence that Seasonal

effective disorder does seem to be

linked to a higher melatonin level so

there is a maybe a hypers sensitivity to

uh light and darkness in these

individuals and that is linked to all

the symptoms that we

described uh light is obviously the

exogenous s game involved here in Winter

we know that the daytime hours reduce

significantly maybe to maybe five or 6

hours a day of natural light if you

consider also people maybe having a 9

to5 job it means that they will

potentially never be exposed to natural

light in the winter

months so for A3 we can look at the

evidence that uh light is implicated in

uh in Seasonal effective disorder

because phototherapy that means light

exposure is effective yeah uh here we've

got Eastman treated uh Seasonal

effective disorder patients with bright

light or a placebo and they found that

those treated with the real light rather

than the placebo were more likely to

respond uh and sometimes they had a full

remission of symptoms meaning they

weren't clinically that depressed

anymore however 60% uh of sufferers um

found a reduction after treatment but

30% seem to improve after a placebo so

there's the question as to whether light

or other factors psychological factors

rather than uh exogenous light gers are

also involved in Seasonal effective

disorder for example in the winter

months uh our bills will be higher

because we have to use more artificial

light so our electric bills will be

higher our gas bills will be higher

because we have to keep the heating on

in the winter months we have Christmas

that although it's very festive for some

people it's qu could be very depressing

especially if they don't have close

friends or family to spend it with it

might make them feel very lonely and

also lifestyle in the winter you're less

likely to go out you're less likely to

go out for a walk because it's cold

because it's dark so those might also be

factors that um exacerbate people's low

mood these are all confounding variables

because they go along with the winter

months we can't separate them and study

them so they're not extraneous variables

that we could control for they're

confounding that do impact on what we're

researching and there's basically

nothing we can do about

that lastly another factor that has to

be noted is that not everyone exposed to

reduced daylight develops Seasonal

effective disorder because everybody is

experiencing winter months and but not

everybody is falling into depression so

that means that there are genetic

predisposition uh overall uh issues with

mental health that make it more likely

for some people than other to develop

Seasonal effective disorder therefore uh

questioning the extent to which it is a

matter of exogenous and endogenous

factors and whether it's something

completely separate