Biopsychology Flashcards
(25 cards)
The divisions of the nervous system - CNS
The Brain - The Central Nervous System consists of the brain and the spinal cord. The brain’s outer layer, the Cerebral Cortex, is highly developed in humans than in any other animal. It is what we see when we picture a human brain, the grey matter with a multitude of folds making up the outer layer of the brain. It is involved in a variety of higher conscious thought, emotional, sensory, and motor movement functions.
The brain is divided into two symmetrical hemispheres: left (language, the rational half of the brain, associated with analytical thinking and logical abilities) and right (involved with musical and artistic abilities). These are divided up into four distinct lobes. Under the cerebral cortex is the area of the brain which is more primitive and are concerned with vital functioning and instinctive behaviour.
The Spinal Cord:
The spinal cord is a white bundle of nerves, which runs from your brain along a canal in your backbone. It’s approximately 40cm long and as wide as your thumb for most of its length. Similar to the brain, the spinal cord is part of your central nervous system. Its main function is to pass messages to and from the brain. It is also involved in reflex actions.
The divisions of the nervous system - PNS
The PNS consists of nerves outside the brain and spinal cord. It is divided into two major systems, the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS)
The Somatic Nervous System (SNS) is part of the PNS that is concerned with the interaction of the outside
world. It controls the voluntary movement of skeletal muscles. It also consists of the nerves that carry messages to the eyes, ears, skeletal muscles and
the skin to give the CNS experience of its environment.
The Autonomic Nervous System (ANS) Is the part of the
PNS that controls involuntary movement from non-skeletal muscles, for example, the ‘smooth muscles’ that control the intestines, digestion, bladder, pupil size and the cardiac muscle.
The ANS is split into two further systems: The Sympathetic and the Parasympathetic nervous
systems.
The Sympathetic Nervous System is activated in situations requiring arousal and energy. When we feel threatened or under stress, the sympathetic branch of the ANS is activated which starts the instinctive reaction of ‘fight or flight’, aiding survival. It produces increased heart and respiratory rate, increasing blood flow to the muscles and pupil dilation.
The Parasympathetic Nervous System is activated soon after the threat of danger has passed. This has the opposite effect of the Sympathetic Nervous System and allows for the body to return to homeostasis. Here the person’s heart and respiratory rate decrease to normal levels and blood flow decreases. The pupils return to normal size. This system is vital for the individual to conserve energy and not to become exhausted
The structure and function of sensory, relay and motor neurons
Sensory neurons, located in the peripheral nervous system (PNS) respond to stimulation in sensory
receptors. They send signals to the spinal cord and brain about this sensory experience. There are sensory neurons for all senses. Most sensory neurons have long dendrites and short axons. Sensory neurons carry signals away from the organ to the brain and spinal cord.
Motor neurons are cells in the PNS that send messages from the brain and the spinal cord to the muscles and glands . These usually have long axons and short dendrites.
Relay Neurons form connections between other neurons. They can send signals to other relay neurons, or form links between sensory and motor neurons. All neurons in the CNS are relay neurons, and there are over 100 billion relay neurons
Synaptic transmission
Electrical impulses are passed through the axon of a neuron to the synaptic terminal (1).
The electrical impulse cannot go through the gap between neurons, the synaptic gap/cleft.
Instead the electrical impulse causes calcium to be released (2)
This triggers vesicles (little sacs) that
contain neurotransmitters to be released (3).
The released neurotransmitters cross the synapse (4).
They then bind to the receptors on the post-synaptic neuron (5)
This triggers a signal in the post-synaptic neuron (6).
(Neurotransmitters can have an excitatory
effect on the receiving neuron - making them more likely to fire - or an inhibitory effect - making them
less likely to fire).
Exitation and inhibition
Neurotransmitters have either an excitatory or inhibitory effect on the post synaptic neuron. For example, the neurotransmitter GABA causes an inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire. In contrast, acetylcholine has an excitatory effect on the neighbouring neuron by increasing its positive charge, therefore making it more likely to fire an impulse.
The endocrine system
Hypothalamus - This is connected to the pituitary gland and it stimulates and controls the release of hormones from the pituitary gland.
Pituitary gland - Oxytocin Thyroid Stimulation Hormone (TSH) ACTH - The ‘Master gland’ as it controls all other glands, for example, TSH signals action in the thyroid, ACTH signals action in the adrenal glands.
Thyroid gland - Thyroxine - Primarily involved with the regulation of metabolism, such as the conversion of food into energy for the muscles.
Parathyroid gland - Parathormone
PTH - essentially acts to increase the concentration of
calcium in the blood from kidneys and bone.
Pancreas - Insulin - Promotes the absorption of glucose from the blood into fat, liver and skeletal muscle cells.
Adrenal glands - Adrenaline & Noradrenaline - Responsible for reacting to threat via the fight or flight
response.
Ovaries (female) - Oestrogen and progesterone - Responsible for the development and regulation of
the female reproductive system and secondary sex
characteristics.
Testes (male) - Testosterone - A key role in the development of male reproductive system such as the testes and prostate, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair.
Pineal gland - Melatonin - Regulates the Sleep-wake cycle
Localisation of function
Localisation suggests that different functions of the brain are localised in specific areas and are
responsible for different behaviours, processes or activities.
Motor area - A region in the frontal lobe involved in regulating movement
Somatosensory area - An area of the parietal lobe that processes sensory information (e.g. touch)
Visual area - A part of the occipital lobe that receives and processes visual information
Auditory area – Located in the temporal lobe and concerned with analysis of speech.
Language centres
Broca’s area – An area of the frontal lobe in the left hemisphere (in most people) responsible for speech production
Wernicke’s area- An area of the temporal lobe (encircling the auditory cortex) in the left hemisphere (in most people) responsible for language comprehension
Localisation of function - Evaluation
Arguments for localisation:
Brain scan evidence of Localisation
Petersen et al (1988) used brain scans to demonstrate how Wenicke’s area was active during a listening task and Broca’s area was active during a reading task. These
findings support a theory of localisation as the findings evidence specific areas of the brain having specific and different functions.
Neurosurgical evidence
Surgically removing or destroying areas of the brain to control behaviour was developed in the 1950s. Controversially neurosurgery is still used today to treat extreme cases of psychological disorders.
Dougherty et al (2002) reported on 44 OCD patients who had undergone a cingulotomy which is a procedure that cuts the cingulate gyrus. Findings showed a third of patients significantl improved and a further 14% showed partial improvement. The success of these procedures
strongly supports that the symptoms and behaviours of mental disorders are localised.
Case study evidence
The Case of Clive Wearing- An individual with brain damage as of a result of a viral infection had damage to his semantic long term memory however little damage to his procedural memory. This suggests localisation because if the function was spread throughout the entire brain there would not be specific deficits in this way. However, a case study only provides evidence, not proof.
Arguments against localisation:
Challenging theory and research Lashley (1950) the work of Karl Lashley suggests higher cognitive process such as learning are not localised but distributed holistically
Lashley removed between 10-50% of areas of the cortex in rats. The rats were learning a maze. No particular area was shown to be more important in terms of the rats’ ability to complete the maze. This suggests the process of learning required every part of the cortex. This seems to suggest learning is too complex to be localised,
supporting a more holistic and multifunctional theory in regards to the function of the brain. Criticisms of Lashley’s study however relate to the fact that the research was conducted on animals. This means we should be cautious in drawing conclusions related to human learning as we know the human brain is much more complex.
Plasticity - The notion of cognitive mapping or plasticity is a compelling argument against localisation. Evidence shows that when the brain has become damaged
through illness or accident and a particular function has been compromised or lost, the rest of the brain appears to be able to reorganise itself to recover the function. An example of this is in stroke victims many of whom seem to able to recover abilities that were seemingly lost as a result of illness (E.g. speech)
Plasticity
This refers to the fact that the brain can change and develop as a result of our experience and learning, and also that it can recover after trauma. The brain changes throughout the lifespan. During infancy, the brain experiences a rapid growth in the number of synaptic connections there are to other neurons, peaking at around 15,000 at age 2-3 years. This is around twice as many as there are in the adult brain. As we age, connections that we don’t use are deleted and connections that we use a lot are strengthened.
This process is known as synaptic pruning.
Research into Brain Plasticity
Maguire et al (2000) studied the brains of London taxi drivers and found that there was a significantly greater volume of grey matter in the posterior hippocampus than in a matched control group. This part of the brain is associated with spatial and navigational skills in humans
and other animals. Part of a London taxi driver’s training involves taking a test known as ‘the knowledge’, which assesses their ability to recall the names and locations of the streets in the city.
The results of the study suggest that the learning the drivers undertake as part of their training alters the structure of their brains. It was also noted that there was a positive correlation between how great the volume of grey matter was and how long they had been in the job. (The longer the participant had been driving the taxi, the larger his hippocampus). This suggests evidence
(correlational) for structural differences in the brain due to extensive experience of spatial
Kuhn et al (2013) found a significant increase in grey matter in various regions of the brain after participants played video games (Super Mario 64) over a period of 2 months for 30 minutes per day. (Comparison to a control group). This shows evidence for brain plasticity and shows how experience (playing games) can result in structural changes in the brain.
Draganski et al (2006) imaged the brains of medical students three months before and after their final exams. Learning induced changes were seen to have occurred in the posterior hippocampus and parietal cortex, presumably as a result of the exam. Mechelli et al (2004) found a larger parietal cortex in the brains of bilingual people, compared to non-bilingual people.
Functional Recovery of the Brain after Trauma
Functional Recovery of the Brain after Trauma
The brain is often able to recover from trauma that is caused by physical injury or illness (e.g. stroke). This is another example of neural plasticity. Unaffected areas of the brain are often able to adapt and compensate for the areas that have been lost or damaged. Healthy brain areas may take over the functions of the areas that have been affected. Neuroscientists suggest that this process can occur quickly after the trauma, but then slow down after several weeks or months. The person may then require rehabilitative therapy to assist their recovery.
How Does Brain Recovery Work?
The brain is able to reorganise and rewire itself by forming new synaptic connections close to the area of damage. Secondary neural pathways that would not usually be used to carry out certain functions are activated to enable functioning to continue, often in the same way as before. Support for this comes from structural changes that are known to take place in the brain.
Examples are:
Axonal sprouting: The growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways
Reformation of blood vessels
Recruitment of homologous (similar) areas on the other side of the brain to take over specific tasks
These new connections are activated and compensate for nearby damage areas of the brain, therefore recovering any damage occurring in specific regions.
Research:
Laura Danelli et al (2013) investigated EB, a 17yr old Italian boy who had his entire left brain hemisphere removed at 2yrs old. (Due to non-cancerous tumour).
By 5ys, his language fluency improved due to intensive rehabilitation and by 17, using various brain scans, although there were minor problems with his grammar, in his everyday life, EB’s language appeared virtually normal. Suggesting language abilities can still function even after severe trauma, such as the removal of the left hemisphere.
Evaluation of plasticity and functional recovery after trauma
Practical application
Our increased understanding in this area has contributed to the treatment of those who have suffered brain trauma. The fact that we know that spontaneous brain recovery slows down after a few weeks, means that
we are aware of when it may be necessary to start physical therapy to maintain improvements in functioning. Also, electrical stimulation of certain parts of the brain following particular damage following injury or
strokes. This suggests the brain has the ability to fix itself to a certain extent, but some intervention is likely to be necessary if full recovery is to be achieved.
Negative plasticity
The brain’s ability to rewire itself does not always have positive consequences. Some adaptations may be unhelpful. Prolonged drug use, for example, has been shown to result in poorer cognitive functioning as well as an increased risk of dementia in later life. Also, 60-80% of amputees are known to develop phantom limb
syndrome. This is the continued experience of sensation in the missing limb. These sensations are usually unpleasant and painful and are thought to arise from cortical reorganisation in the somatosensory cortex
that results from the limb loss. This shows that there can be a negative consequence of the brain rewiring itself, although there are treatments that aim to help individuals
that have seen positive results. Individual differences:
Age & Gender
Functional plasticity tends to reduce with age, and this therefore affects the speed of recovery. Marquez de la Plata et al (2008) found that, following brain trauma, older patients (40+ years old) regained less function in treatment than younger patients and they were also more likely to decline in terms of function for the first five years following the trauma. However, Bezzola et al (2012) found that 40 hours of golf training produced changes in the neural representation of movement in participants aged between 40 and 60. Using fMRI they found that motor cortex activity was reduced for the novice golfers compared to a control group. Suggesting more efficient neural representation after training. This supports the view that neural plasticity does continue throughout the lifespan. There is also evidence to suggest that women
recover better from brain injury because their function is not as lateralised. (concentrated in one hemisphere)
Individual differences:
Education
Evidence suggests that the person’s level of educational attainment will influence how well the brain recovers after trauma. Schneider (2014) found that the more time brain injured patients had spent in education, (known as their cognitive reserve) the greater their chances of a
disability-free recovery. This suggests that the cognitive reserve could be an important factor in brain recovery after trauma.
Split brain research
Lateralisation
The ability to produce and understand language, for most people, is controlled by the left hemisphere. This suggests that for the majority of us, language is
subject to hemispheric lateralisation. In other words, the specialised areas associated with language are found in one of the hemispheres rather than both.
In the late 1960’s, Sperry and his colleagues began to conduct a number of experiments investigating this, this collection of research became known as ‘split-brain
research’.
Sperry’s studies involved a unique group of individuals, all of whom had undergone the same surgical procedure – an operation called a commissurotomy – in which
the corpus callosum and other tissues which connect the two hemispheres were cut down the middle. This was done as a treatment for people who had frequent and
severe epileptic seizures, because separating the two hemispheres would help to control seizures.
This meant for the split brain patients the main communication line between the two hemispheres was removed. This allowed Sperry and his colleagues to see the extent to which the two hemispheres were specialised for certain functions and whether the
hemispheres performed tasks independently of one another.
Sperry’s procedure
Sperry devised a way of being able to test hemispheric lateralisation using visual and tactile tasks. This involved using a piece of equipment called a ‘T-scope’ (see below) which allowed each hemisphere to be tested in isolation of the other.
The general procedure involved the participant being asked to focus on the ‘fixation point’ and then an image or word was projected very quickly (1/10th of a second) to one or both visual fields. For example, the word ‘key’ could be projected so that it only is processed by the participant’s right visual field (processed by the left hemisphere) and then the same, or different, image could
be projected to the left visual field (processed by the right hemisphere). To test for non-verbal processing, this equipment also enabled the participants to be able to pick up or match objects that were out of the participant’s sight.
In a ‘normal’ brain, the corpus callosum would immediately share information between both hemispheres giving a complete picture of the visual world. However, presenting the image to one hemisphere of a split-brain patient meant that information could not be conveyed from that hemisphere to the other
Key findings from his original study.
- When a picture/word was projected to the right visual field (information processed in left hemisphere), the patient could easily describe what had been shown. However when the picture/word was projected to the left visual field (information processed in right hemisphere), the patient could not describe what had been shown and typically reported that there was nothing there. This supports hemispheric lateralisation showing that language is processed in the left hemisphere as the patients could only describe what they had seen when it was projected to the right visual field
- Although the patients could not describe what had been shown to their left visual field, they were able to use their left hand to point to a matching object or picture. This shows that the right hemisphere has processed the information but obviously cannot verbalise what was shown.
- If two words/pictures were projected simultaneously, one on either side of the visual field (e.g. ‘a dollar sign’ on the left and ‘a question mark’ on the right), the patient would say that they saw a question mark but when asked to draw (with their left hand) what they saw, they would draw a dollar sign. The patients were not aware that they had drawn a different object or picture to the one they said they had seen. This suggests the two hemispheres were working separately from each other. It also suggests that drawing ability is dominant in the right hemisphere.
- An object placed in the patients right hand (the patient could not see it just feel it) it could be easily described or named in speech or writing, whereas, if the same objects were placed in the left hand, the patient could only make
wild guesses. However, when this object is taken from them and placed in a grab-bag along with other objects, the patient is able to search for and retrieve the object with their left hand. This also supports hemispheric lateralisation as it shows the left hemisphere is dominant for speech and writing. It also shows again that the right hemisphere is able to comprehend what the object is but
just cannot identify it verbally.
Evaluation of split brain research
For
Split brain research is experimental and involves the use of specialised equipment that can objectively measure the lateralisation of function in each hemisphere. The use of this equipment allows for the image or word to be projected extremely quickly (1/10th of a second) to one or both visual fields. This meant that the split-brain patients would not have time to move their eyes across the image and so the visual information would only be processed by one visual field (and one hemisphere) at a time, therefore
increasing the internal validity of the research.
The standardised procedures used in the research, for example giving the same tasks to each participant and using standardised equipment (the T-scope) have helped to enable the research to be checked for reliability. The same procedure has been used on a number of split-brain patients and the results on the left hemisphere being dominate for language has been found to be consistent.
Against
The control group used by Sperry were people with no history of epileptic seizures therefore they could be seen as an inappropriate group to use as a comparison. As the
split brain patients suffered from epilepsy, it could be argued that it may have caused unique changes in the brain which could have influenced the results, so a more
appropriate control group would have been people who had a history of epilepsy but had not had the split-brain procedure.
Small sample sizes are used in split brain research meaning it is difficult for the results on hemispheric lateralisation to be generalised to the wider population. However, as commissurotomy is a rare procedure, there is a limited amount of ‘split brain’ patients available for investigation therefore small sample sizes are unavoidable.
The data gathered from the split brain research came from the patients being testing under artificial conditions. In real life a severed corpus callosum can be compensated for by the unrestricted use of two eyes therefore the research findings cannot be generalised to how split brain patients function in everyday tasks.
Ways of investigating the brain - FMRI
Functional magnetic resonance imaging (fMRI). fMRI works by detecting the changes in blood oxygenation and flow that occur as a result of neural (brain) activity in specific parts of the brain.
When a brain area is more active it consumes more oxygen and to meet this increased demand blood flow is directed to the active area (known as the haemodynamic response).
fMRI produces 3-dimensional images (activation maps) showing which parts of the brain are involved in particular mental processes and this has important implications for our understanding of localisation of function.
Strengths
Unlike other scanning techniques, fMRI does not rely on the use of radiation. If administered correctly it is virtually riskfree, non-invasive and straightforward to use. Therefore, it can be used to measure activity in the brain without causing harm.
It produces images that have very high spatial resolution, showing detail by the millimetre, and therefore providing a clear picture of how brain activity is localised
Weaknesses
fMRI is expensive compared to other neuroimaging techniques and can only capture an image if the person stays perfectly still.
It has poor temporal resolution (doesn’t show changes over time accurately). So in the scan picture above the
highlighted areas appear 4/5 seconds after the brain activity occurred. This means findings could be misinterpreted.
fMRI can only measure blood flow in the brain, it cannot tell us the exact activity of individual neurons and so it can be difficult to tell what kind of brain activity is being represented on the screen.
Ways of investigating the brain - Electroencephalogram (EEG)
EEGs measure electrical activity within the brain via electrodes that are fixed to an individual’s scalp using a skull cap.
The scan recording represents the brainwave patterns that are generated from the action of millions of neurons, providing an overall account of brain activity.
The main 4 types of EEG waves are alpha, beta, theta and delta.
Scientists can also measure brain activity through amplitude and frequency. Amplitude is the intensity or size of activity, frequency is the speed or quantity of activity
Strengths
EEG is valuable at helping diagnose conditions such as epilepsy and schizophrenia because the difference in
brain activity can be detected on the screen i.e. schizophrenic patients may display ‘unusual’ EEG wave patterns. This is useful for clinical diagnosis.
It has contributed to our understanding of the sleep stages and sleep problems. Strengthening the usefulness of EEG.
It has extremely high temporal resolution (unlike fMRI) it records brain activity in real time. Therefore, researchers can monitor responses to tasks.
Weakness
EEG represents brainwave patterns and as such it cannot detect activity in deeper brain regions. Therefore, if there were issues to a patient’s hippocampus, an EEG wouldn’t necessarily pick up this
information. Suggesting the limitation of this technique.
EEG is not useful in pinpointing the exact source of neural activity (the activity of many thousands of neurons) and therefore it’s hard to work out which
area of the brain the waves originate from, highlighting a further limitation of this technique.
Ways of investigating the brain - Event-related potentials (ERPs)
ERP’s use similar equipment to EEG (electrodes attached to the scalp) however, a stimulus is presented to a participant i.e. picture or sound, and the researcher looks for activity related to the stimulus and investigate how an EEG wave pattern changes in response to the stimulus. This change is an ERP. (Types of brainwaves triggered by particular events).
The stimulus is presented hundreds of times and an average response is graphed. This is a statistical averaging technique, and it reduces any extraneous brain activity which makes the specific response to the stimulus stand out.
Strengths
The limitations of EEGs being too general are partly addressed by ERPs- they are much more specific to the measurement of neural processes.
They provide a continuous measure of processing in response to a stimulus. Therefore, this provides quantitative experimental data.
Researchers have also been able to identify ERP’s of mental health issues like phobias. It has been found that people with phobias have ERP’s of a greater amplitude (intensity of activity) in response to images of the objects they feared compared to non-phobic individuals. This allows researchers more of an understanding of complex mental processes.
Weakness
There is a lack of standardisation in ERP methodology between different research studies, which makes it difficult to confirm findings.
It may not always be possible to completely eliminate background noise and extraneous material needed to
establish pure data in ERP studies, therefore validity may be questionable.
Ways of investigating the brain - Post-mortem examinations
This is a technique involving the analysis of a person’s brain following their death.
In psychological research, individuals whose brains are subject to a post-mortem are likely to be those who have a rare disorder and have experienced unusual deficits in mental processes or behaviour during their lifetime.
Areas of damage within the brain are examined after death as a means of establishing the likely cause of the affliction the person suffered. This may also involve comparison with a typical brain in order to determine the extent of the difference between them.
Strengths
Post-mortem evidence was vital in providing a foundation for early understanding of key processes in the brain. Broca’s and Wernicke’s areas were identified using post-mortem
Post-mortem studies improve medical knowledge and help generate hypotheses for further study. E.g. Zhou
analysed the brains of female-male transsexuals and found an area of the brain associated with gender to be
larger in these individuals- more similar to that of a male.
This demonstrates the beneficial nature of post-mortems in our understanding of gender development.
Weakness
Causation is an issue within these investigations. Observed damage in the brain may not be linked to the deficits under review but to some other unrelated trauma or decay. (For example drugs and age may affect brain tissue). Therefore, there are issues with cause and effect being established.
They raise ethical issues of consent from the patient BEFORE death. – A patient may have significant brain abnormality when alive and are therefore too ill to
give consent for their brains to be investigated upon their death. This poses an ethical concern as a postmortem may still be carried out
Circadian rythms
The most obvious circadian rhythm in humans is the sleep-wake cycle. It is a 24 hour rhythmic cycle where there are differing levels of consciousness. People sleep for a certain time every 24 hours, and conduct other activities during wakefulness. The fact that we feel drowsy when it’s night time and alert during the day
shows the effect of daylight (exogenous zeitgeber) in our sleep/wake cycle. However, what would happen if the biological clock was ‘left to its own devices’ without the influence of light
Research
Siffre’s cave Study
In 1962 Michel Siffre spent two months living in complete isolation in a cave to study the effects on his own circadian rhythm. He was deprived of natural light, a clock, a calendar and sound, but had access to adequate food and drink. He slept and ate only when his body ‘told him to’. Therefore, the only influence was his internal body clock (endogenous pacemaker). Siffre re-surfaced in mid-September 1962 believing it to be mid-August! He believed the date to be a month earlier than it was. His lack of external cues made him feel a day was actually ‘longer’ than it was and fewer days had passed in total.
A decade later he performed a similar feat for six months in a cave in Texas. In each case, his ‘free running’ circadian rhythm settled to around 25 hours.
Other research…
Aschoff and Wever (1976) asked a group of participants to spend four weeks in a WWII bunker. The participants were shielded from natural light (no windows), temperature changes or other environmental cues.
They had access to artificial light and could switch it on/off. Similar to Siffre, they displayed a circadian rhythm of approximately 25 hours. (One participant extended to 29 hours). These studies suggest the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but we use natural light to entrain our pacemakers associated with the 24 hour clock.
Furthermore, circadian rhythms are not easily overridden by external cues…
Simon Folkard et al (1985) studied a group of 12 participants who agreed to live in a dark cave for 3 weeks, isolating them from natural light. The researchers manipulated the clock. Participants would retire when the clock read 11.45pm and awoke when it read 7.45am. Over the course of he study, the researchers speeded up the clock (unbeknown to participants) so what they believed was a normal 24 hour day was in fact only lasting 22 hours. Interestingly, only one of the participants could adjust comfortably to new regime! This seems to suggest the existence of a strong free running circadian rhythm that cannot be easily overridden by changes in the external environment.
Circadian rythms - Evaluation
Small sample sizes and generalisation
As fascinating as the research is in this area, it tends to involve small groups of participants and in the case of Siffre, one individual. The people involved may not be representative. This therefore limits the degree to which meaningful generalisations can be made and applied to the wider population.
Confounding variables Although the participants in Aschoff and Wever’s study were deprived of natural light, they still had access to artificial light. Siffre would turn on
a lamp every time he woke up which remained on until he went to bed. It was assumed that artificial light would have no effect on his free running circadian rhythm however other research Czeisler 1999, suggests the opposite, that artificial light can have an influence. This
means the use of artificial light could have been a confounding variable and affected the validity of the results.
Individual differences
Linked with generalisation is that individual cycles can vary, some people have a natural preference for going to bed early and rising early (known as ‘larks’) whereas others prefer the opposite (‘owls’). There are also age differences in sleep/wake patterns. Thus, individuals
seem to have innate differences in their cycle length and onset and these individual differences can further complicate generalisation.
Practical applications to shift work
Research has provided a better understanding of the consequences of disrupted circadian rhythms i.e. shift work. Night workers can experience reduced concentration around 6am, making mistakes and
accidents more likely. Poor health has been linked with night shifts. This highlights economic implications and how changes in shift work patterns could help workers stay healthy and manage productivity.
endogenous factors
Sleep is not a random human function. It is influenced by particular factors both inside and outside us. endogenous pacemakers refer to an internal body clock that sets many of our bodily rhythms, including sleep. The internal body clock that has an effect on when
we sleep and when we are awake is the suprachiasmatic nucleus (SCN). Exogenous zeitgebers are external cues that have an influence on when we’re sleep or awake, such as light.
Inside the body.
.The main endogenous pacemaker (internal) is the
suprachiasmatic nucleus (SCN) or biological clock.
It’s a bundle of nerves located in the hypothalamus
of the brain.
.The SCN is located above the optic area ( i.e. Optic
nerve & optic chiasm)
.Therefore, it can receive information about light directly. The SCN passes the information about day length/light to the pineal gland.
.Based on this information, the pineal gland will release melatonin (a chemical that makes us feel sleepy).
During the night, the pineal gland increases melatonin production. With more daylight, less melatonin. The SCN is therefore to a degree regulated by light from our outside world.
.However, even in the absence of any light (trapped
in a cave). The SCN generates a rhythm related to its
production of protein. When it reaches a certain
level of protein it passes a message to the pineal
gland and melatonin will still be released or inhibited.
.So although daylight influences the SCN it’s not
absolutely essential. (Think of a person who is blind,
they still have a sleep/wake cycle regardless of light
input).
Research supporting the SCN:
Morgan’s hamster study - Morgan removed and transplanted the SCNs from hamsters and shows support the importance of the SCN as an endogenous pacemaker. Hamsters were bred so that they had a circadian rhythm of 20 hours rather than 24. The SCN cells from these abnormal hamsters were transplanted onto the brains of normal hamsters. These normal hamsters began to adopt the same abnormal circadian rhythm as their 20 hour donor. Furthermore, when hamsters with nocturnal patterns of activity (usual) had their SCNs replaced with SCNs from mutated hamsters which slept through the night and were active during the day (unusual), the hamsters followed the new daytime activities of the donor’s patterns. Further evidence from lesioning (cutting) the SCN in rats showed a complete disruption to the animals sleep/wake cycle.
This suggests the transplanted SCN had imposed its pattern onto the hamsters and shows the significance of the SCN and how endogenous pacemakers are important for biological rhythms
exogenous factors
Let’s now turn to exogenous zeitgebers, or external cues.
The most influential exogenous zeitgeber is light, (zeitgeber is German for ‘time giver’) and it’s an
important factor in our environment that ‘resets’ our biological clocks, this is called entrainment. Light enters the eye through the retina and this information is passed onto the SCN. (Another example of zeitgebers would be social cues such as meal times). The main point is that although most of the processes are internally driven, it can be governed by the exogenous zeitgeber of light.
Low levels of light (retina) goes… Via the Optic area to the SCN SCN sends signals to pineal gland Pineal gland releases melatonin Induces sleep
Research supporting exogenous zeitgebers:
Campbell and Murphy (1998)
An innovative study by Campbell & Murphy showed that light may be detected by skin receptor sites on the body, even when the same information is not received by the eyes. 15 participants were woken up at various times and a light pad was shone on the back of their knees.
The researchers found a change in their sleep/wake cycle of up to 3 hours in some cases. This suggests that light is a powerful exogenous zeitgeber that doesn’t need to rely on the eyes to exert influence on the brain
Infradian rythms
Infradian rhythms have cycles that occur longer than 24 hours. The best example is the female menstrual cycle because it occurs monthly. The cycle begins from the first day of a woman’s period, when the womb lining is shed, to the day before her next period. The ‘average’ cycle takes about 28 days to complete, however it varies with every woman and can be anywhere between 21days (short cycle) and 35 days (long cycle). Every woman’s cycle is different.
Hormones:
Being a biological rhythm the menstrual cycle is governed by changes in hormones. One of the most important hormones is oestrogen and this is at its highest around half way through the cycle during ovulation. At this point an egg is released from the ovary. After ovulation, another hormone called progesterone also increases in preparation for the possible
development of an embryo and this ‘preparation’ is the womb lining starting to thicken with blood, getting the womb ready for pregnancy. If pregnancy doesn’t occur, the egg is absorbed back into the body, the lining of the
womb sheds, and this is the menstrual flow.
Research supporting the infradian rhythms: menstrual cycle
Reinberg (1967) conducted a study where one female participant spent three months in a cave with only light from a small lamp. Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days. This suggests that the lack of light (an exogenous zeitgeber) affected the woman’s menstrual cycle, and therefore demonstrates the effect of external factors on
infradian rhythms. (This research relates to the exam hint).
A further study
McClintock and Stern (1998)
Aim: to show that the menstrual cycle is influenced by pheromonal secretions from other women.
Sample: 29 female university students, not taking birth control pills.
Design: A Longitudinal experiment with independent measures.
Method: Samples of pheromones were gathered from 9 of the women at different stages of their menstrual cycle, via a cotton pad placed under their armpit. The pads were worn for at least 8 hours to ensure pheromones were picked up. The pads were treated with alcohol and frozen (to eliminate any bacteria). This was the control group. The odour from these pads were inhaled by the other 20 women (the experimental group) by being rubbed on their upper lip. On day 1, pads from the start of the cycle were applied to the 20 women, on day 2 they were given pads from the second day of the cycle, and so on.
Result: when the experimental group inhaled secretions from women who were about to ovulate, their menstrual cycles became shorter. When they inhaled secretions from women who had just ovulated, their menstrual cycles became longer. The experimental groups’ menstrual cycles were affected by the secretions from the control group. On 68% of occasions the recipients of the sweat donation had experienced changes to their cycle which brought them closer to their ‘odour donor’. (Synchronised)
Conclusion: This possibly explains why when a group of women live in close proximity their menstrual cycles tend to synchronise and provides support for the role of exogenous zeitgebers (pheromones) in infradian rhythms.
Infradian rythm - Evaluation
Methodological limitations in synchronisation studies
Individual differences
McClintock’s research has criticisms that suggest there are numerous factors other than pheromones that could change a woman’s cycle, such as stress, diet, exercise etc. that may act as confounding variables. Furthermore, research involves small samples of women and relies on women self-reporting the onset of their own cycle. Therefore, these ‘other factors’ both methodological and individual differences, make the influence of pheromones on infradian rhythms questionable.
Replication
Recent replication of research between women’s cycles in close proximity has failed to find evidence of menstrual synchrony suggesting reduced reliability.
Animal studies/pheromones
The knowledge gained about pheromones is mainly from animal studies, in animal sex selection. In contrast, evidence for definite effects of pheromones in human behaviour is still questionable and again poses doubt on the validity of pheromones affecting the menstrual
cycle.
Evolutionary approach
Evolutionary psychologists suggest a possible reason for women’s menstrual cycles synchronising is that it provides an evolutionary advantage for groups of women – in other words the synchronisation of pregnancies means that childcare can be shared among multiple
mothers who have children at the same time due to a couple of reasons firstly, women lactating at the same time (having breast milk) and secondly, through the release of oxytocin – mothers are able to bond to babies.
Therefore, these factors mean that ultimately synchronisation of women’s menstrual cycles will enhance survival.
Ultradian rythm
Ultradian Rhythms: The cycles of sleep
These occur less than 24 hours and a good example are the stages of sleep. A typical night’s sleep takes you from stage 1 to 4 then back to 2 and finally into REM. Sleep is the perfect example of an ultradian rhythm (one that repeats itself over a period of less than 24 hours)
One cycle of sleep typically lasts about 90 minutes and during a typical night’s sleep we will repeat this cycle four or five times, although the cycles do differ through the night.
Sleep stages:
Stages 1 and 2 are ‘light sleep’ stages: Brain patterns become slower starting with alpha waves, progressing to theta waves.
Stages 3 and 4 are ‘deep sleep’ associated mainly with delta waves.
Stage 5 (REM sleep). The body is ‘paralysed’ to prevent acting out our dreams. The eyes rapidly move from side
to side. The brain activity resembles a person who is awake.
Stages 1-4 are NREM stages (Non REM)
Stage 5 is REM stage
On average the entire cycle repeats every 90 minutes and a person may have 4 or 5 full cycles per night
Supporting research
Dement and Kleitman (1957)
Aim: The aim of this laboratory experiment was to investigate the relationship between eye movements and dreaming.
Method: The nine participants were seven adult males and two adult females. The participants were studied under controlled laboratory conditions. Participants had to report to the laboratory at bedtime where they were connected to an EEG. The EEG took measurements throughout their time asleep all night. P’s were asked not to drink caffeine.
Results: The results show that REM sleep is predominantly, though not exclusively, associated with
dreaming, and Non-REM sleep is associated with periods of non-dreaming sleep. P’s were able to recall dreams when awakened during REM periods. If they were awakened in other stages they were less likely to report dreaming. The REM periods occurred at regular intervals during the night, though each participant had their own pattern: the mean period between each REM phase for the whole group was 92 minutes, with individual norms varying between 70 minutes and 104 minutes.
Supporting evidence
In 1964 Randy Gardner remained awake for 264 hours. While he experienced numerous problems such as blurred vision and disorganised speech, he coped incredibly well despite his significant sleep deprivation.
After his experience, he slept for just 15 hours and over several nights recovered only 25% of his lost sleep. He recovered about 70% of stage 4 sleep, 50% of his REM sleep and very little of the other stages. These results suggest the wide degree of flexibility in terms of the different stages within the sleep cycle and the variable
nature of this ultradian rhythm.
