REVISE Biopsychology in 40 mins! (AQA A-level Psychology) transcript

Hey everyone, welcome back to bear it in mind. This video is going to summarize the whole of the biocsychology topic. This is designed to give you an overview. So if you want more in-depth explanations of any part of biocsychology, you can find a full playlist of videos on each section on the bear it in mind YouTube channel. And if you want more help with your revision to study smarter and save you time, you can join Bear It in Mind where you'll find a variety of resources from interactive quizzes, exam paper, walkthrough videos, exemplar answers, and much more.

The link is in the description. First, let's talk about the nervous system. Your nervous system can be broken down into two main parts. The central nervous system and peripheral nervous system. The central nervous system is called the central nervous system partly because it's in the center of your body. It's made up of your brain and spinal cord. Then there is the peripheral nervous system. The word peripheral means on the edge or the outer part.

The peripheral nervous system is where nerve cells carry information to or from the central nervous system. As we just saw, the central nervous system is made up of the brain and spinal cord. The spinal cord is connected to the brain and sends information to the brain from the outer parts of the body, the peripheral nervous system, and sends signals from the brain out to the peripheral nervous system. The peripheral nervous system can be further split up into two parts.

The somatic nervous system, this is responsible for conscious perception and it's also responsible for voluntary movement of sceal muscles. The sematic nervous system has sensory and motor neurons. It receives sensory information from the outside world and sends this to the brain and in turn sends a signal to the muscles, the motor neurons to bring about action. And there's also the autonomic nervous system. This is responsible for involuntary control of the body including reflex movement of sceal muscles and maintaining organ function.

For example, breathing, heart rate, and stress responses. You don't have to think about breathing. The autonomic nervous system does it for you. Additionally, the autonomic nervous system can be further split into two parts. There's the sympathetic nervous system. This is also known as the fightor-flight response, preparing the body for action. And the parasympathetic nervous system, also known as the rest and digest response, leading the body into a calm state.

In addition to the work of the nervous system, the endocrine system is involved through a network of glands through the body that manufacture and secrete chemical messengers known as hormones. So instead of using nerves to transmit information like the nervous system, the endocrine system instructs glands to release hormones directly into the bloodstream. So the function of the endocrine system is to provide a chemical system of communication via the bloodstream and to secrete the hormones which are required to regulate many bodily functions.

So meet Eddie. Eddie the endocrine system. Let's consider five of his glands, the hormones they release, and the effect they have on his body. Firstly, the pituitary gland. Your pituitary gland is a small p-sized gland located at the base of your brain below your hypothalamus. The pituitary gland is sometimes called the master gland of the endocrine system because it controls the functions of many of the other glands.

The pituitary gland makes certain hormones including oxytocin. In women, oxytocin is involved during childirth by sending signals to their uterus to contract. It also influences bonding between the mother and her baby during breastfeeding. Secondly, the pineal gland is also found in the brain and produces the hormone melatonin. Melatonin helps regulate our sleep and synchronizes our sleep wake cycle with night and day.

As your melatonin levels increase, your body temperature and blood pressure drop, preparing your body for sleep. Moving away from the brain, there is the thyroid gland. The thyroid gland produces the hormone thyroxine. Thyroxine controls how much energy your body uses called the metabolic rate. It's also involved in digestion, how your heart works, as well as brain development. When the thyroid gland does not make enough thyroxine, many of the body's functions slow down.

The adrenal glands near the kidneys produce the hormone adrenaline, which stimulates the sympathetic nervous system and brings about the fight and flight responses. Finally, the testes are two male reproductive glands that produce sperm and the hormone testosterone. This hormone causes the development of male characteristics such as growth of facial hair and deepening of the voice. Higher levels of testosterone are also associated with aggression.

So finally, let's explore how these two systems, the nervous system and the endocrine system work together in the fightor-flight response, which includes the role of adrenaline. Starting with the central nervous system which is the brain. When we perceive a stressor, a part of the brain triggers activity in the peripheral nervous system, specifically in the autonomic nervous system, specifically the sympathetic nervous system.

The autonomic nervous system changes from its normal resting state, the parasympathetic state, to the physiologically aroused sympathetic state. This activates the fightor-flight response. Now we come to the endocrine system. The adrenal gland releases the hormone adrenaline into the bloodstream. Adrenaline causes a number of changes in the body. All of this happens in an instant as soon as the threat is detected. Once the stressor has passed, the parasympathetic nervous system returns the body to its resting state.

It's referred to as the rest and digest response. Next, the structure and function of neurons. Neurons enable communication within the nervous system. And these neurons transmit signals electrically and chemically within a neuron. Signals are transmitted electrically where the electrical signal starts at one end and travels along to the other end. You need to understand the parts of a neuron and their function. The cell body.

This includes a nucleus which contains the genetic material. Dendrites. These are branch-like structures that come out of the nerve cell to connect with other neurons. They receive information from other neurons and send nerve impulses towards the cell body. The axon, this carries nerve impulses away from the cell body and the length of axons varies from a few millimeters to over a meter in the spinal cord. The myelin sheath this insulates and protects the axon and helps to speed up the electrical transmission along the axon.

Nodes of Romevier. These are the gaps in the myelin sheath that force the impulse to jump across the gaps along the axon. This helps increase the speed of the electrical impulse. Terminal buttons. At the end of the axon are terminal buttons that send impulses to the next neuron across the sinapse. The sinapse is the gap between one neuron and the next neuron. The terminal buttons contain tiny sacks containing chemicals called neurotransmitters.

You need to know the function of sensory relay and motor neurons. Sensory neurons typically look like this. Their function is to carry messages from your peripheral nervous system to your central nervous system. Motor neurons typically look like this. Their function is to carry nerve impulses from the central nervous system toectors such as muscles and glands. Relay neurons typically look like this. Relay neurons are found in the brain and spinal cord. and relay neurons carry nerve impulses between neurons connecting the sensory and motor neurons.

Between neurons, signals are transmitted chemically. This process is called synaptic transmission. Synaptic transmission is the process by which neighboring neurons communicate with each other by sending chemical messages across the gap. Neurons do not actually touch one another. Each neuron is separated from the next neuron by a tiny gap called the sinapse. Sinapses allow electrical messages to travel from one neuron to an adjacent neuron by transmitting signals chemically using neurotransmitters.

Well, how does this happen? To explain this process, try remembering V R E R R S. V for vicles. When the impulse reaches the end of the axon, it arrives at the presinaptic terminal. Pre means before. So, presinaptic means before the sinapse. These are made up of small structures called vicles and contain neurotransmitters. R for release. The electrical impulse that is traveled down the axon triggers the release of the neurotransmitters which then diffuse across the sinapse known as the synaptic cleft.

R for receptors. And these neurotransmitters are received by receptors on the dendrites of the next neuron specifically known as the postsinaptic receptor sites. Post meaning after. So post-saptic equals after the sinapse. The neurotransmitter is converted back into an electrical impulse and carries on down the axon of the neuron. E for enzymes. Enzymes are released to break down any neurotransmitters still in the sinapse.

R for re-uptake. Also some neurotransmitters go through a process called re-uptake where any excess neurotransmitters still there are reabsorbed back to the presinaptic terminal. R for replenished. Vicles are replenished with new and reused neurotransmitters ready for the next impulse. Now whether the neuron fires and passes on the electrical impulse to the next neuron depends on whether the neurotransmitters that are received at the post-saptic receptor site have either an excitatory or inhibitory effect on the next neuron.

Excitation is when a neurotransmitter increases the positive charge of the postsinaptic neuron. This increases the likelihood that the neuron will fire and pass on the electrical impulse. Inhibition is when a neurotransmitter increases the negative charge of the postsaptic neuron. This decreases the likelihood that the neuron will fire and pass on the electrical impulse. So what affects whether the neuron will fire and pass on the electrical impulse or not?

The answer is summation. This basically means that the excitatory and inhibitory influences are summed or totaled. If the total effect on the post synaptic neuron is inhibitory i.e negative in total then the neuron is less likely to fire. If the total effect is excitatory i.e positive in total the neuron will be more likely to fire. In the 19th century holistic theory was the dominant view of the brain at the time. This is the idea that all parts of the brain are involved in thought processes and action.

However, the research of Paul Brocker and Cal Vernicker led to a different theory, localization of function. This is the theory that different areas of the brain are responsible for different functions or behaviors. The frontal lobe is thought to be responsible for movement of the body, personality, and higher level thinking such as concentration, planning, and problem solving. The motor area of the brain, motor meaning movement, is located at the back of the frontal lobe.

The parietal lobe is thought to be involved with your senses such as touch and pressure, taste, and body awareness. It is home to the brain's primary sensory area, a region where the brain interprets information from other areas of the body. The smata sensory area is located here behind the motor area. S meaning body and sensory meaning senses. So body senses. The occipital lobe is thought to be responsible for sight.

And so this is where the visual area is. The temporal lobe is thought to be responsible for receiving and processing sounds. And so this is where the auditory area is. Now let's look at language. The brain has two hemispheres, left and right. And for most people, language is localized in the left hemisphere. There are two main language centers you need to know. Brocker's area located in the left frontal lobe is responsible for speech production.

Damage here can cause Brock's aphasia where speech becomes slow and effortful. Then there's Vernica's area in the left temporal lobe near the junction with the parietal and occipital loes. This area helps us understand language. Damage here leads to Vernica's aphasia. Speech is fluent but comprehension is poor. So what evidence supports localization of function? Let's start with Brocker and tan. In 1861, Paul Brocker studied a patient who could only say the word tan.

After the patient died, Brocker found a large lesion in his left frontal lobe. This suggested that this specific area, now known as Brock's area, controls speech production. Next, Vernica studied patients who could speak fluently but didn't understand language. He found damage in a different area, now called Vernick's area, supporting the idea that different parts of the brain control different language functions. Then there's Phineas Gage.

In 1848, an iron rod went through his skull during a railway accident. He survived, but his personality completely changed. This suggested that the frontal lobe is involved in personality, emotional control, and decisionmaking. But not all evidence is so clear-cut. In 2007, Drunkatal used an MRI scan on the preserved brain of patient Tan studied by Paul Brocker. They found damage in other areas beyond Brocker's area.

And this suggests speech production may involve multiple brain regions, not just one. So the brain might be more complex and connected than strict localization suggests. There's also the issue that many of these studies involve rare unusual cases. This means it's hard to generalize the findings to the wider population, a limitation in the evidence. One of the strongest arguments against localization is the concept of brain plasticity.

Brain plasticity refers to the brain's ability to change and adapt as a result of experiences. For example, stroke patients can sometimes regain lost abilities as healthy areas of the brain take over the damaged functions. This flexibility suggests that while certain areas may specialize in specific tasks, the brain is also capable of functioning in a more holistic way. Hemispheric lateralization is the idea that certain mental functions are more dominant in one side of the brain than the other.

One of the most fascinating things about the brain is that the left hemisphere actually controls the right side of the body and the right hemisphere controls the left side of the body. This is known as contraateral organization. If someone has a stroke and loses movement on the right side of their body, it usually means the stroke occurred in the left hemisphere. And because language is also typically in the left hemisphere, that can also affect their ability to speak.

L Brocker studied a patient known as Tan because regardless of the question he was asked, he always responded tan tan. He clearly had a problem with speech production. When Brocker carried out a postmortm examination on his brain, they found lesions in his left frontal lobe leading to the suggestion that the ability to produce speech is located in this area. This is localization of function. Additionally, Brocker went on to study eight other patients who had similar language problems.

All of these patients had lesions in their left frontal hemisphere. And then there's Vernicus aphasia. Calver's patients all had lesions in the brain in the left temporal lobe and they had problems not with producing speech but with comprehending speech. Notice from these cases that language appears to be lateralized. The ability to produce and understand speech appears to be in the left hemisphere. We can deepen our understanding of hemispheric lateralization by looking at split brain research.

In some patients with severe epilepsy, doctors surgically cut the corpus colossum, the bundle of nerve fibers connecting the two hemispheres to prevent seizures spreading across the brain. This gave researchers like Roger Sperry and Michael Gazoniger an amazing opportunity to study how separate the two hemispheres really are. To understand their experiments, you need to know how vision works. You have a left and right visual field.

Information from your left visual field goes to your right hemisphere and information from your right visual field goes to your left hemisphere. In their experiment, Sperry and Gazoniger showed visual information to just one visual field at a time. They did this by having patients stare at a fixed point on a screen and flashing images to either the left or right side for just one/tenth of a second. So they didn't have time to move their eyes and so prevent the information going to both hemispheres.

Let's go through a few of their tasks. First, the describe what you see task. If the image of an apple was flashed to the right visual field, the patient would say they saw an apple. This is because the information from the right visual field is processed by the left hemisphere which as we've seen is thought to be for speech and language and so the split brain patient can respond verbally and say they saw an apple. However, if the image of an apple was flashed to the left visual field, the patient would say that they saw nothing.

This is because the information from the left visual field is processed by the right hemisphere which can see the picture. But as it has no speech and language abilities whilst it knows it's an apple, it cannot share this information with the left hemisphere where the ability to speak is located and so says nothing. Finally, in the drawing task, participants were presented with a picture in either their left or right visual field, and they had to simply draw what they saw.

If presented to the left visual field, which would go to the right hemisphere, they could clearly draw the picture with their left hand. If presented to the right visual field, which would go to the left hemisphere, the image they drew with their right hand was never as clear. It became evident that the left hemisphere is specialized for language whereas the right hemisphere is specialized for visual motor skills. One of the main strengths of this research is how scientific it was.

The experiments were highly controlled and standardized. For example, showing images for just one/tenth of a second ensured only one hemisphere saw the image. This precision made the results very reliable and replicable. There are also some criticisms. First, not all the patients had the same degree of separation between the hemispheres. Some had more of the corpus glossom cut than others, which could affect the results.

Second, there were issues with the control groups. The control participants didn't have epilepsy, so they weren't directly comparable to the split brain patients who had severe neurological issues. Third, some patients had been on medication for longer than others, which could also affect their brain function. Another issue is the small sample size. Split brain studies often involve only a handful of patients, all of whom had severe epilepsy.

That makes it hard to generalize the findings to the general population. This is called a lack of population validity. And finally, there are some contradictory findings. For example, Gazonager himself wrote an article in 1998 titled the split brain revisited in which he reported on a patient referred to as JW. Split brain research had suggested that the right hemisphere was unable to handle even the most basic language.

However, his patient JW had now developed the capacity to speak out of the right hemisphere with the result that he could now speak about information presented to the left or to the right brain. All as a result of the brain's ability to change and adapt called brain plasticity. Brain plasticity is the brain's ability to change its structure and function in response to experience. A long time, scientists thought this kind of change only occurred in childhood.

But more recent research shows that the brain can continue to adapt and reorganize throughout our entire lives, even into older age. Let's look at some psychological research that helped demonstrate this. First up, a study by Keermanal in 1997. They wanted to see if the environment could physically change the brain. And they tested this on rats. 24 rats were split into two groups. The control group lived in standard lab cages with food and water.

The other group, the lucky ones, lived in a much more stimulating environment. They found that the rats in the enriched environment developed more new neurons in their hippocampus, a brain area involved in memory and learning. This showed that life experience, in this case, a more stimulating environment, can literally change the physical structure of the brain. However, it's worth noting that this study was done on rats.

And while they're commonly used in research, there are big differences between rat and human brains, especially in terms of language, social interaction, and emotional complexity. So, we should be cautious when applying these findings to people. So, what about research with humans? Elellanena Maguire and colleagues in 2000 conducted research on the brains of 16 right-handed male London taxi drivers with an average of 14 years experience and compared them with 50 right-handed male non- taxi drivers.

To do this, they scanned the brains of each participant using an MRI machine which provided an image of the structure of the brain. When they compared the images, they found that the London taxi drivers showed a larger posterior hippocampus compared to the control group. The taxi drivers experience of navigating the streets of London placed such a high demand on their spatial processing that the brain changed its structure.

Kunatal in 2014 compared a control group who played no video games with a video game group who were trained for two months on the game Super Mario playing for at least 30 minutes per day. Two months later, when they scanned the brains of both groups in an MRI machine, they found a significant increase in gray matter in the prefrontal cortex, hippocampus, and cerebellum. This increase was not seen in the control group who didn't play video games.

The researchers concluded that the experience of playing video games had resulted in new synaptic connections in brain areas involved in spatial navigation, strategic planning, working memory, and motor performance. all the skills needed to play the game successfully. It retal in 2012 studied 11 participants aged 40 to 60 years old who were all noviceses at golf. These noviceses then had 40 hours of golf practice and were compared with a control group matched in terms of age and sex who didn't have any golf training.

They scanned their brains at the start of the study and then again after the experimental group had completed their 40 hours of practice. The participants were instructed to imagine with their eyes closed their own golf swing from a firstperson perspective and in slow motion. They found reduced activity in the motor cortex in the brain, the area responsible for movement. While reduced activity in the brain suggests that the experience of playing golf had changed the structure of the brain.

The repeated golf practice had refined the pathways in the brain for the golf swing. The brain had become more efficient in its neural pathways. Functional recovery refers to the brain's ability to regain lost functions following an injury by rrooting activity to undamaged areas. Here are three key processes. Axonal sprouting. When you hear the word sprouting, think of plants growing new shoots. You may remember that neurons contain axons that help transmit information.

But when an axon is damaged, its connection with other neurons is lost. Axonal sprouting is when undamaged axons sprout or grow new nerve endings to replace the old ones in order to reconnect to other neurons. Axonal sprouting can bridge the connection and so enable the communication in the brain to continue. Secondly, neuronal unmasking. The brain contains dormant sinapses. Dormant meaning it's alive but not active.

These are connections between neurons which have no function. They are there but they are not currently being used. When brain damage occurs, these dormant sinapses become activated so that they can take on the function that was lost because of the brain damage. The neurons were there but inactive but now they are unmasked so that they are used to help recover the lost function. Thirdly, recruitment of homologous areas.

The word homologous means similar. So this is where similar areas sometimes in the other hemisphere are used when an area of the brain is damaged. For example, if Brock's area was damaged on the left side of the brain, the right-sided equivalent would carry out its functions. Now, let's consider two case studies that provide evidence for functional recovery after trauma. At age three, Jod had such severe seizures that doctors remove the entire right hemisphere of her brain.

Incredibly, her left hemisphere took over many of the lost functions. Secondly, there is the case study reported by Danellial in 2013. They studied an Italian boy referred to as EB who had most of his left hemisphere removed at age 2 and a half years because of a tumor. They studied EB up to the age of 14 and reported amazing results. Initially, he unsurprisingly had problems with language. However, within two years following the surgery, he had recovered most of his language skills.

Over the years, his language was assessed as near to normal. When they scanned his brain with an fMRI machine, they found brain patterns for language tasks in the right hemisphere that you would typically find in the left hemisphere. But not everyone recovers in the same way. Let's look at three key factors that can influence how well the brain can bounce back. Age. You probably noticed both Jod and EB were very young.

That's no coincidence. The younger the brain, the more plastic it tends to be and the more likely it is to recover lost functions. Schneider and colleagues found that people with higher levels of education, like university degrees, were more likely to make a good recovery from brain injury. Finally, gender may also play a role. Ratcliffe studied 325 patients a year after traumatic brain injury and found some differences.

Females perform better on tasks involving attention and working memory and males perform better on visual analytical skills. This suggests recovery may also depend on which cognitive abilities are affected and who is recovering. The word post means after and the word mortm means death. So after death. So a postmortem is an examination of a dead body and specifically for our purposes it's the examination of the brain after death.

Number one, behavior. Firstly, they study the individual's behavior whilst they are alive. There may be something particularly abnormal about a person's behavior, which has meant they've been referred to a doctor or psychologist for assessment. Their strange behavior could suggest that there might be damage in the brain that is behind these problems. Two, brain. Next, they study their brain after death. When the person dies, the researchers can examine the brain to look for abnormalities and lesions in the brain.

Importantly, their brain is compared to a normal brain in order to identify differences. Three, correlation. Finally, the analysis of the brain allows the researcher to form a correlation between the abnormal behavior of the patient and a particular area of the brain. Now let's evaluate postmortems. One strength of postmortems is the level of detail they gather about the brain. Postmortems allow for the examination of the structure of the brain beyond the cerebral cortex.

That's the outer part of the brain near the skull. And it can provide insight into deeper regions of the brain such as the hippocampus areas that are inaccessible for certain brain scanning techniques like EEGs. However, one of the limitations with postmortems relates to cause and effect. This is because postmortems are forming a correlation between a person's behavior during their life and the damage in their brain.

The damage in the brain could have been caused by another factor such as a head injury or an illness. Another issue with postmortems as a way of studying the brain relates to ethical issues particularly around informed consent. In this case, patients will be giving consent to their brain being analyzed through a postmortem when they die. For example, patient HM had severe amnesia and couldn't form new memories. So, it's questionable whether he could have truly consented to a postmortem.

Here's three steps to describe how fMRIs study the brain and our behavior. Number one, blood flow. This way of studying the brain measures blood flow in the brain whilst a person performs a task. Two, oxygen. If an area of the brain becomes more active, those neurons in the brain use the most energy and require more oxygen. Three, magnetic oxygen is released for use by these active neurons at which point the hemoglobin which carries the oxygen in the blood becomes deoxxygenated.

Deoxxygenated hemoglobin has a different magnetic quality from oxygenated hemoglobin and that's what the magnet detects. One of the main strengths of fMRIs relates to spatial resolution. This is because fMRI machines have high spatial resolution of approximately 1 to 2 millm which is significantly greater than the other techniques such as EEGs and ERPs. Therefore, this suggests that fMRIs can provide more insight into the brain's activity because it offers a more accurate way of studying the brain.

However, one of the limitations of fMRIs relates to temporal resolution. This is because fMRI scans have low temporal resolution of around 1 to 4 seconds, which is not as good as other techniques. For example, EEGs have a temporal resolution of 1 to 10 milliseconds. EEGs stand for electro and seephlograms. It's the measurement of the electrical activity of the brain over time. One, electrodes. This way of studying the brain measures electrical activity of brain cells and neurons through electrodes attached to the scalp.

Information is processed in the brain as electrical activity in the form of action potentials or nerve impulses. Two, intensity and frequency. The EEG is able to pick up the size or intensity of electrical activity as well as the frequency or rate of electrical activity. Three waves. Electrical signals from the different electrons are plotted on a graph that provides the data in the form of four different types of waves.

These are known as alpha, beta, delta, and theta waves. Event related potentials use electrodes to measure very small voltage changes within the brain when patients are presented with a stimulus such as a picture or sound which requires cognitive processing. So to condense this down to three steps. One, specific. ERPs study the brain by measuring very small voltage changes in the brain that are triggered by specific events or stimuli.

Two, averaged. To establish a specific response to a specific event or stimulus requires many presentations of the stimulus, and these responses are then averaged together. Three, filtered out. Using a statistical averaging technique, all background brain activity from the original EEG recording is filtered out so that the event related potential, the response to the specific event is left. So let's now evaluate both EEGs and ERPs as ways of studying the brain.

Firstly, one strength of EEGs is that they are effective tools for diagnosing certain brain disorders. For example, as we have seen, EEGs can be used to monitor stages of sleep and people can have their brain monitored whilst they are sleeping to diagnose any sleep problems. Additionally, EEGs are successfully used in diagnosing epilepsy as seizures are reflected in abnormal brain wave patterns. A strength of both EEG and ERPs is that they are cheaper than fMRIs.

For example, at the time of recording this video, the cost of an EEG machine is anywhere between $1,000 and $25,000, whereas an fMRI machine costs anywhere between half a million and $3 million. This means that EEGs and ERPs are more accessible for a wider range of people and further means that larger sample sizes from studies can be used to draw conclusions about the brain's activity. Another strength of EEGs and ERPs relates to temporal resolution.

This is because EEGs have high temporal resolution as they take readings of the electrical activity in the brain every millisecond. This means it can record the brain's activity in real time as compared to having to wait 1 to 4 seconds for an image of the brain's activity like an fMRI. However, as you can probably guess, the limitation of EEGs and ERPs relates to spatial resolution. This is because EEGs have low spatial resolution as they only detect the general activity of the cerebral cortex, the outer part of the brain and not specific areas.

EEGs are unable to provide information on what is happening in the deeper regions of the brain such as the hippocampus making this technique limited compared to fMRI. Finally, biological rhythms. Biological rhythms are repeated patterns of changes in the body that are regulated by an internal clock. There are three types of biological rhythm that you need to know. Circadian rhythms last for around 24 hours. The word circa is Latin for about in DM is Latin for day.

So it means about a day. An example of a circadian rhythm is the sleepwake cycle. Endo is Greek for inside and genus is Greek for producing. Endogenous pacemakers are internal body clocks that regulate our biological rhythms. So this means that inside you and me is a clock. A clock that decides when we fall asleep and when we wake up. Exo is Greek for outside and zeitge is German for timegiver. Exogenous sight givers are external cues that influence and reset our internal biological clocks.

So, is there something inside your body that is controlling and maintaining your sleepwake cycle? It's called the supra caismatic nucleus or the SCN for short. The SCN is a tiny cluster of nerve cells located in the hypothalamus. The SCN is thought to be the endogenous pacemaker for our sleepwake cycle. So, what about exogenous zeitge then? The external cues that influence our rhythms. Well, one of the most powerful external cues that influences our sleepwake cycle is light.

In fact, the SCEN, our internal clock, receives information about light through our eyes and the optic nerve. And believe it or not, the SCEN can even detect light when our eyes are shut. When there is less light, the SCEN stimulates the pineal gland to produce more melatonin, which helps us fall asleep. And when there is more light, melatonin production reduces to help us feel awake. Firstly, Darcia in 2000 conducted research with chipmunks.

A control group of 20 normal chipmunks with perfectly intact seen were compared with an experimental group of 30 chipmunks who had their seen destroyed. Each chipmunk was radiocollled so that they could be tracked and then they were released back into their natural habitat where they were observed for 80 days. What they found was that more chipmunks who had their seen damaged were killed by weasels compared to the control group.

Why? Because their sleepwake cycles were disrupted. They were active at times when they should have been asleep, making them easier prey. This shows just how important the SEN is in regulating circadian rhythms and helping animals and humans survive. But we should be cautious. These findings come from animal research and humans might not operate in exactly the same way. So results may not fully generalize. Now for some human research, meet Michelle Cif, a French researcher who conducted a famous cave study in 1962.

He spent two months underground in total darkness. No clocks, no natural light to test if humans have an internal clock. While in the cave, Se monitored his body's rhythms, including when he slept and woke up. What did he discover? Even with no exposure to natural light, his body still followed a regular sleepwake cycle, though it was closer to 25 hours instead of 24. This suggests that we do have an internal biological clock.

Our natural cycle might be slightly longer than 24 hours, and we need exogenous sight givers like light to keep our clocks aligned to the real world. But se had artificial light in the cave, which could have affected his results. That's where Caesar Italy 1999 come in. They found that even artificial indoor lighting can influence the seen, contradicting earlier assumptions that only bright natural light mattered. Understanding circadian rhythms isn't just academically interesting.

It has real life applications. There's a whole field called chronootherrapeutics, the study of how timing affects medical treatment. For example, some studies have shown that the effectiveness and side effects of cancer treatments can depend on what time of day the medication is given. This means doctors can optimize treatments based on the body's natural rhythms, helping improve outcomes and reduce harm. Infraadian rhythms take longer than 24 hours to complete one cycle.

The example we're going to consider is the menstrual cycle. The menstrual cycle is the time from the first day of a woman's period to the day before her next period. The length of the menstrual cycle on average is around 28 days, but this can vary between 23 to 35 days. In 1971, Mcccleintoch studied 135 females who lived together in college dorms. She found that the more time the women spent together, the more their menstrual cycles began to align.

This suggested that something in the environment was influencing their cycles, leading them to synchronize. But what was it? Mcccleintoch herself raised the possibility that pherommones could be the cause. To investigate further, Mcccleintoch did another study of 29 women. Pherommones were collected from nine of the women by having them wear cotton pads in their armpits for eight hours. These pads were then treated and rubbed on the upper lips of the other participants. 68% of the women experienced changes in their cycle that brought them closer to the woman whose pherommones they were exposed to.

That suggests that pherommones might act as exogenous sight givers influencing this infra rhythm. However, there are some important criticisms. For one, replication has been a problem. In one piece of research, they studied 186 Chinese women living in dorms with four to eight women per room, perfect conditions for pherommonal synchronization if it were real. But they found no synchrony over a full year of tracking. They argue that the findings from mccllintok studies may have been random or influenced by other factors.

Finally, there are alradian rhythms. These are cycles that last less than 24 hours. So, we experience multiple cycles per day. A great example is the stages of sleep. When you and I sleep, we go through cycles of about 90 minutes. And within each 90 minute cycle, we pass through multiple stages of sleep. Sleep is divided into two main categories. Nonrem sleep, non-rapid eye movement, and sleep, rapid eye movement. REM sleep is sometimes known as paradoxical sleep because your brain waves look more like when someone is awake.

The amount of non-REM and REM sleep within a 90-minute cycle changes throughout the night with the first half of the night spent mostly in non-REM and the second half of the night consisting of more REM sleep. And the REM sleep is when we are thought to dream. In a now classic study, William Dement and Nathaniel Kleman used EEG machines to record sleeping and dreaming. Specifically, they wanted to see if there were any differences in dreaming between non-REM and REM sleep.

There were nine participants in the study, seven male and two female, but only five of these were studied in detail. Shortly before their normal bedtime, they would arrive at the lab where they went to sleep with electrodes from the EEG attached to their scalp. They found that when they were woken up during non-REM sleep, participants could rarely remember their dreams, around 7%. In contrast, when woken up during REM sleep, they could often vividly describe their dreams around 80% of the time.

Therefore, this study demonstrates that there are distinct stages to our sleep. However, research into the stages of sleep have been criticized in relation to its samples. This is because the samples used in these studies are often very small, as can be seen with the five studied by Dement. Such a small number makes it hard to generalize the results to others, especially when there could be individual differences in people's biology, hormones, and age, which might all influence sleep.

And finally, a further issue with research into alt trading rhythms relates to the settings in which they take place. This is because sleep laboratories are very artificial settings. Studying sleep in this manner could lead to people's sleep stages being altered compared to normal. And therefore, it could be argued that the research into alteration rhythms lacks ecological validity as it's not reflecting ordinary sleep.

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