Psychology - Biopsychology (AO1)

What is the nervous system?

1. The organised network of nerve tissue in the body.

2. Consists of the central nervous system and peripheral nervous system.

What is the central nervous system (CNS)?

1. Consists of the brain and the spinal cord where it is the origin of all commands and decisions.

What is the peripheral nervous system (PNS)?

1. Sends information to the CNS from the outside and transmits messages from CNS to muscles and gland.

What is the somatic nervous system?

1. Transmits information from receptor cells in sense organs to the CNS.

2. Receives information from the CNS that directs to muscles.

3. Voluntary movement.

What is the autonomic nervous system?

1. Transmits informations to and from internal bodily organs.

2. The system is 'autonomic' hence the system is involuntary.

What are the two main functions of the nervous system?

1. Collect, process and respond to information in the environment.

2. Coordinate with different working organs.

What is the two subsystems of the nervous systems?

1. Central nervous system (CNS)

2. Peripheral nervous system (PNS)

What is the CNS made up of?

The brain and the spinal cord.

What is the outer layer of the brain called?

cerebral cortex

What are the subsystems of the peripheral nervous system?

1. Autonomic nervous system

2. Somatic nervous system

What is the difference between ANS and SNS?

Somatic:

1. Voluntary

2. Controls muscles and movement

3. Has sensory and motor pathways.

Autonomic:

1. Involuntary

2. Controls internal organs and glands.

3. Has only motor pathways.

What is the endocrine system?

1. Works alongside the nervous system to control vital functions in the body.

2. Works much slower than the nervous system.

3. Associated with hormones.

What is the function of the endocrine system?

1. To secrete hormones that are needed for regulating bodily functions.

2. Such as the release of the required amount of a specific hormone to promote appropriate metabolism.

What is the pituitary gland known for?

1. Known for being the called the master gland.

Where is the pituitary gland located?

base of the brain

What does the pituitary gland do?

1. Controls the release of hormones from all the other endocrine glands.

What hormone does the pituitary gland release?

ACTH

What hormone does the adrenal gland release?

adrenaline

What does adrenaline do?

1. Prepares body for physical action (fight or flight)

2. Strong effect on cardiovascular cells - stimulates heart rate.

What is the role of adrenaline in the fight or flight response?

1. Adrenaline is released from the adrenal medulla by the activation of the sympathomedullary pathway.

2. The body goes from the parasympathetic state to the sympathetic state.

3. The general effects of adrenaline: prepares the body for the fight or flight response. Increases blood supply to skeletal muscles/

4. Direct effects such as increased breathing rate, heart rate and sweat.

What is the fight or flight response?

1. Physiological arousal that prepares the body for fight or flight response.

2. The release of adrenaline.

3. A quick response to the stressor to fight the threat or run away.

What is the process of fight or flight?

1. The stressor is perceived.

2. The hypothalamus triggers activity in the sympathetic strand.

3. The ANS changes from the parasympathetic state to the sympathetic state.

4. Stress hormone adrenaline is released from the adrenal medulla into the bloodstream.

5. Adrenaline increases the heart rate which creates a physiological arousal for fight or flight response.

6. Once threat has passed, the body goes back to the parasympathetic strand.

Give me three examples of the sympathetic state.

Choose from:

1. Increases heart rate

2. Increases breathing rate.

3. Dilates pupils.

4. Inhibits digestion.

5. Inhibits salivary production

6. Contracts rectum

Give me three examples of parasympathetic state.

Choose from:

1. Decreases heart rate

2. Decreases breathing rate.

3. Constricts pupils.

4. Stimulates digestion.

5. Stimulates salivary production

6. Relaxes rectum

What are the three types of neurons?

sensory, motor, relay neurons

What is the sensory neuron?

1. These carry information from PNS to the CNS.

What is the relay neuron?

1. These connect sensory neurons to other relay neurons or motor neurons.

What is the motor neuron?

1. These connect the CNS to the effectors such as muscles and glands.

What is the difference between all neurons?

1. Sensory neuron had long dendrites and short axons.

2. Relay neurons have short dendrites and short axons.

3. Motor neurons have short dendrites and long axons.

What is the structure of the neuron?

1. Nucleus - within the cell body - stores genetic information of the cell.

2. Dendrites - branch-like structures that carries nerve impulse to the cell body.

3. Axon - carries impulse away from the cell body down the length.

4. Myelin sheath - fatty layer to protect the axon - speeds up transmission segmented by gaps called the Nodes of Ranvier.

What is the process of synaptic transmission?

1. The action potential arrives at the presynaptic terminal.

2. The synaptic vesicles containing neurotransmitters fuse with the presynaptic membrane and releases the neurotransmitters into the synaptic cleft.

3. The neurotransmitter diffuses across and binds to the receptors on the postsynaptic membrane.

4. Stimulation of the neurotransmitters can be either excitatory or inhibitory.

What is summation?

1. Excitatory and inhibitory influences are summed.

What is localisation of function in the brain?

1. Scientists in the early 19th century supported the holistic theory that all parts of the brain were involved in processing thought and action.

2. But specific areas were later linked with specific physical and psychological functions.

What is the brain divided into?

1. The brain is divided into two symmetrical halves called the left and right hemisphere.

2. Some of our physical and physiological functions are controlled by a particular hemisphere and this is known as lateralisation.

The brain is subdivided into four centres called the 'lobes' of the brain, what are they and their roles?

1. At the back of the frontal lobe is the motor area - controls voluntary movement in the opposite side of the body. If damaged, results in a loss of control over fine movements.

2. At the front of both parietal lobes is the somatosensory area - where sensory information from the skin is represented.

3. In the occipital lobe at the back of the brain is the visual area - eye sends information from the right visual field to the left visual cortex etc. If this is damaged, can cause blindness.

4. In the temporal lobe is the auditory area - analyses speech-based information. If this is damaged, this may produce partial hearing loss.

What are the language centres of the brain?

Broca's area and Wernicke's area

What is the broca's area and what is it responsible for?

1. Paul broca identified a small area in the left frontal lobe responsible for speech production.

2. If damage is caused to the broca's area, this causes broca's aphasia which is characterised by speech that is slow and lacking in fluency.

What is the Wernickes area and what is it responsible for?

1. Wernicke identified a region in the left temporal lobe as being responsible for language understanding.

2. If this area was damaged, this would cause Wernicke aphasia where they would produce nonsense words often.

What is one strength of localisation of function of the brain? hiNT: pHINEAS gage

1. Unique cases of neurological damage supports the localisation theory such as the case of phineas gage who received serious brain damage in an accident.

2. Gage survived but the damage to his brain affected his personality - he went from someone who was calm and reserved to quick tempered and 'no longer gage'.

3. The change in Gage's temperament following the accident suggests the frontal lobe may be responsible for mood.

However.. Hint: case studies

1. There are problems with case studies.

2. Difficult to make meaningful generalisations from findings of a single individuals.

3. It is not certain that the changes gAGE went through would have occurred for someone else.

4. We may not know how Gage was before the accident.

5. It's hard to replicate the study as usually case studies are from rare situations from individuals.

What is one limitation of the localisation theory? Hint: language centres questioned.

1. One limitation is that language may not be localised just to Broca's or Wernicke's area.

2. A recent review by Dick and Tremblay found that only 2% of modern researchers think that the language in the brain is completely controlled by broca's area and wernicke's area.

3. Advances in the brain imaging techniques such as fMRI, mean that neural processes in the brain can be studied with more clarity.

4. It seems that language function is distributed far more holistically in the brain than was first thought.

5. Language streams have been identified across the cortex, including brain regions in the right hemisphere.

6. This suggests that rather than being confined to key areas, language may be organised more holistically in the brain.

What is hemispheric lateralisation?

1. Concerns behaviours controlled by one hemisphere.

2. In case of language, the two main centres are only in the left hemisphere - Broca's area in the left temporal lobe and Wernicke's area in the left temporal lobe. So we say that language is lateralised.

What is the left hemisphere responsible for?

1. speech

2. comprehension

3. arithmetic

4. analytical thinking

What is the right hemisphere responsible for?

1. creativity

2. spatial ability

3. artistic

4. musical skills.

What is one strength of hemispheric lateralisation? Hint: research support.

1. One strength is research showing that even in connected brains the two hemispheres process information differently.

2. Fink et al used PET scans to identify which brain areas were active during a visual processing task.

3. When ppts with connected brains were asked to attend to global elements of an image, regions of RH were much more active.

4. When required to focus in on finer detail, the specific areas of LH tended to dominate.

What is 'split brain' operation?

1. This involves severing the connections between the RH and the LH, MAINLY the corpus callosum.

2. Surgical procedure to reduce epilepsy.

Who conducted split brain research?

Sperry

What did sperry investigate?

He devised a system to study how two separated hemispheres function when they cannot communicate with each other.

What was the procedure of sperry's study?

1. Eleven people who had split brain operation were studied where an image was shown to the patient'S RVF (processed in LH) and another image shown to the patients LVF (processed in RH).

2. In the normal brain, the corpus callosum would share the information between hemispheres giving a complete picture of the visual world.

3. But presenting the image to one hemisphere of a split-brain patient meant that information could not be conveyed to the other hemisphere.

What did Sperry find? (describing what was seen)

1. When a picture of an object was show to a ppts RVF, the patient could describe what could be seen, but they could not do this if it was shown to the LVF - they said nothing was there.

2. This is because in the connected brain, messages are relayed from the RH to the language centres in the LH, but this is not possible in split-brain.

What did sperry find by recognition of touch?

1. Objects were shown to the LVF and could not name them but could select a matching object using the left hand.

2. Left hand could also select an object that was associated with image presented to LVF.

3. In this case, the person could not verbally identify what they had seen because the LH is need for this but could understand what the object was and select the corresponding object.

What is one strength of split-brain research? Hint: research support.

1. One strength is support from more recent split brain research.

2. Gazzaniga showed that split-brain ppts actually perform better than connected controls on certain tasks.

3. For example, they were faster at identifying the odd one out in an array of similar objects than normal controls.

4. This supports sperry's earlier findings that the left brain and right brain are distinct.

What is one limitation of split-brain research? hint: Causal Issues.

1. One limitation is that causal relationships are hard to establish.

2. The behaviour of sperry's split-brain ppts was compared to a neurotypical control group.

3. None in the control group had epilepsy. This is a major confounding variable. Any differences between the groups may be the result of epilepsy rather than split-brain.

4. Too small sample - 11 people.

5. Some unique features of split-brain ppts cognitive abilities may be due to their epilepsy.

What is meant by plasticity?

1. The brain is plastic in the sense that its structure is not static; synaptic connections are lost, reformed and 'pruned' throughout life, particularly in childhood. They adapt and learn from new experiences around them.

2. As we age, rarely used connections are deleted and frequently used connections are strengthened - this is a process known as synaptic pruning.

3. When you are young, brain is still maturing so if any trauma has occurred, most likely to recover.

4. Plasticity allows the brain to cope better with indirect effects of brain damage e.g. swelling.

What is research into plasticity?

1. Maguire et al studied the brains of london taxi drivers and found more volume of grey matter in the posterior hippocampus than in the matched control groups.

2. This part of the brain is associated with spatial and navigational skills in humans and other animals.

3. London cabbies must take a test that assesses their recall of the city streets and possible routes.

What did Maguire et al find?

1. He found that learning experience alters the structure of the taxi drivers brain.

2. They also found that the longer the taxi driver has been in his job, the more pronounced was the structural difference.

Who looked at imaging of the brains of medical students?

Draganski.

1. He looked at the imagining of brain scan of medical students three months before and after final exams.

2. Learning-induced changes in the posterior hippocampus and the parietal cortex.

What is one limitation of plasticity? hint: not always beneficial

1. One limitation is that it may have negative behavioural consequences.

2. Evidence had shown that the brain's adaptation to prolonged drug use leads to poorer cognitive functioning in later life, as well as an increased risk of dementia.

3. Also 60%-80% of amputees have known to develop phantom limb syndrome - experiencing sensations in the missing limb as its there.

4. These sensations are usually unpleasant, painful and thought to be due to cortical reorganisation in the somatosensory cortex.

5. This suggests that the brain's inability to adapt to damage is not always beneficial.

What is one strength of plasticity? Hint: lifespan

1. One strength is that brain plasticity may be a lifelong ability.

2. In general plasticity reduces with age. However, bezzola demonstrated how 40 hours of golf training produced changes in the neural representations of movement in ppts aged 40-60.

3. Using the fMRI, the researchers observed an increased motor cortex activity in the novice golfers compared to a control group.

4. This shows that neural plasticity can continue throughout lifespan.

What is functional recovery?

1. A form of plasticity.

2. The brain's ability to redistribute or transfer functions usually performed by a damaged area to other healthy area.

What happens in the brain during recovery?

1. The brain rewires and reorganises itself forming new synaptic connections close to the area of damage.

2. This process is supported by a number of structural changes including:

axonal sprouting: the growth of new nerve endings which connect with other undamaged nerve cells to form new neural pathways.

Denervation supersensitivity - when axons that do a similar job become aroused to higher level to compensate for the ones lost.

Recruitment of homologous areas on the opposite side of the brain - specific tasks still can be performed, e.g. broca area damaged, the right side would carry out the functions.

What is one strength of functional recovery? Hint: real world application

1. One strength of functional recovery is its real-world application.

2. Understanding the processes involved in plasticity has contributed to the field of neurohabilitation.

3. Simply understanding axonal growth is possible to encourage new therapies.

4. For example, constraint-induced movement therapy is used with stroke patients whereby they repeatedly practice using the affected part of the body while the unaffected part is restrained.

5. This shows that research into FR is useful as it helps medical professionals.

What is one limitation of functional recovery? Hint: cognitive reserve.

1. One limitation of functional recovery is that level of education may influence recovery rates.

2. Schneider revealed that the more time people with a brain injury had spent in education - taken as indication of their cognitive reserve - the greater chances of a disability free recovery.

3. 40% of those who achieved DFR had more than 16 years of education compared to 10% of those who had less than 12 years of education.

4 This simply implies that people with brain damage who have had insufficient DFR are less likely to have a full recovery.

What are the four ways of studying the brain?

fMRI, EEG, ERP, post-mortem examination

What is fMRI and what is it used for?

1. Highlights active areas of the brain.

2. Detects changes in the blood oxygenation and flow that occur due to neural activity in the brain.

3. When a brain area is more active , it consumes more oxygen and blood flow is directed to that active area.

What is an EEG and what does it measure?

1. shows overall electrical activity.

2. measure electrical activity in the brain via electrodes using a skull cap.

3. Recordings represent brain patterns generated from millions of neurons - shows brain activity.

4. Often used as a diagnostic tool.

What are ERPs and what do they measure?

1. brainwaves related to particular events.

2. Isolating specific responses of neurons to specific stimuli or tasks.

3. Types of brainwave that are triggered by particular events.

What are post-mortem examinations?

1. analysis of the person's brain after their death.

2. areas of the brain are examined to establish the likely cause of deficit or disorder that the person suffered from,

3.

Evaluate Post-Mortem Examinations

1. Strength: foundation for understanding the brain - Broca and Wernicke's are relied on post-mortem examination - they also improve medical knowledge - generate hypotheses for further study.

2. Weakness - causation may be an issue - observed damage may not be linked to deficit under review - raise ethical concern for consent - may not be able to provide consent.

What is a circadian rhythm?

Those rhythms that last for around 24 hours.

What are two examples of circadian rhythms?

sleep/wake cycle and core body temperature

What is the sleep-wake cycle?

1. We feel drowsy at night and alert during the day demonstrates the effects of daylight - an importance of exogenous zeitgebers on our sleep/wake cycle.

2. However the sleep/wake cycle is also governed by endogenous pacemakers - a biological clock left on its own devices without the influence of external.

3. This basic rhythm is governed by SCN which lies just above the optic chiasm and receives information about light from this structure.

What was Siffre's cave study?

1. Demonstrated a free-running circadian rhythm of about 25 hours.

2. siffre spent long periods in dark caves to examine effects of free-running biological rhythm.

3. Two months in the caves of the Southern Alps and six months in a Texan cave.

4. Deprived of exposure to natural light and sound but access to adequate food and drink.

5. In the southern alps, he resurfaced in mid-september thinking it was mid august.

6. hE DID have a regular sleep/wake cycle.

What did Aschoff and Wever do?

1. A group of ppts spent four weeks in a WW2 bunker deprived of light,

2. All but one displayed a circadian rhythm between 24 and 25 hours.

3. Siffre's study and aschoff+weaver showed that the sleep/wake cycle may be slightly longer than 24 hours but entrained with 24 hours exogenous zeitgebers.

What did Folkard et al do and find?

1. Folkard studied a group of 12 people who lived in a dark cave for three weeks, going to bed when the clock said 11:45 pm and waking when it said 07:45 am.

2. The researchers gradually speed up the clocks so an apparent 24 hours actually was 22 hours.

3. Only one ppts adjusted to the new regime.

4. Hence, strong free-running circadian rhythm that cannot easily be overridden.

What is one strength of research into circadian rhythms? Hint: economic implications

1. One strength of research into circadian rhythms is that there is practical application to shift work.

2. E.g. night workers engaged in shift work, experience a period of reduced concentration around 6 in the morning meaning mistakes and accidents are more likely.

3. Research also pointed to a relationship between shift work and poor health - shift workers are three times more likely to develop heart disease than people who work more typical work patterns.

4. This shows that research into the sleep/wake cycle may have real-world economic implication.

However...HINT: correlational methods.

1. Studies investigation the effects of shift work tend to use correlational methods. This means it is difficult to establish whether desynchronisation of the sleep/wake cycle is actually a cause of negative effects.

2. There may be other factors e.g. solomon concluded that high divorce rates in shift workers might be due to the strains of deprived sleep.

3. This suggests that it may not be biological factors that create adverse consequences associated with shift work.

What is one limitation of research into the circadian rhythm? hint: hard to generalise

1. One limitation is that generalisations are difficult to make.

2. Studies of the sleep/wake cycle often use small group of participants or even single individuals e.g.folkards 12 ppts or siffre being alone in his study.

3. Ppts may not be representative of the wider population and this limits making meaningful generalisations. Siffre observed that his internal clock ticked much more slowly at 60 than when we was younger.

4. This suggests that researchers may have ignored an important component confounding variable in circadian rhythm research.

What is infradian rhythm?

A type of biological rhythm with a frequency of less than one cycle in 24 hours.

What is an example of infrared rhythms?

menstruation and seasonal affective disorder.

What is the menstrual cycle in relation to infradian rhythms?

1. The human female menstrual cycle is about 28 days.

2. Rising levels of oestrogen cause the ovary to develop and release an egg.

3. The hormone progesterone helps the womb to thicken and ready for pregnancy but if they do not become pregnant, egg is absorbed into the body and the womb lining sheds and leaves the body.

How is the menstrual cycle a exogenous cycle?

1. Stern and McClintock demonstrated how menstrual cycles may synchronise as a result of influence of pheromones.

2. Studied 29 women with a history of irregular periods. Samples of pheromones were gathered from nine women at different stages for their menstrual cycle , via cotton pad placed in their armpit.

3. Pads were worn for at least 8 hours to ensure that pheromones were picked up.

4. Then they were treated with alcohol and then frozen to be rubbed on the upper lip of ppts.

5. found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their 'odor donor'.

What is seasonal affective disorder (SAD)?

1. Another infradian rhythm.

2. This is a depressive disorder which has a seasonal pattern of onset.

3. Often called the 'winter blues' because symptoms are triggered during winter months when the number of daylight hours become shorter.

4. SAD is caused by the hormone melatonin.

5. During the night, the pineal gland secretes melatonin until dawn when there is an increase in light.

6. During the winter, the lack of light in the morning means secretion of melatonin goes on longer.

What is a strength of infradian rhythms? Hint: evolutionary basis.

1. One strength of menstrual synchrony research is that it may be explained by natural selection.

2. Synchronisation of the menstrual cycle, of the kind observed in the Stern and McClintok study is thought by some to have an evolutionary value.

3. for our distant ancestors, it may have been advantageous for women to menstruate together and become pregnant together.

4. In a social group, this would allow babies who had lost their mother during or after childbirth to have access to breast milk, thereby improving their chances of survival.

5. This suggests that synchronisation is an adaptive strategy.

What is one limitation of infradian rhythms? Hint: studies are flawed.

1. One limitation of synchronisation studies is their methodological shortcomings.

2. There are many factors that may affect change to the menstrual cycle, including stress, changes in diet etc. These may act as confounding variables, which means that they occur by chance.

3. This explains why other studies have failed to replicate.

What is ultradian rhythm?

A type of biological rhythm with a frequency of more than one cycle in 24 hours.

What is an example of ultradian rhythms?

stages of sleep

How does stages of sleep explain ultradian rhythms?

1. psychologist have identified five distinct stages of sleep that altogether span across 90 minutes - a course that occurs throughout the night.

2. Each stage is characterised by different wavelength activities - monitored by EEG.

3. Stage 1-2: light sleep, person may be easily woken. Brain waves have high freq but low amp (alpha waves)

4. Stage 3-4: deep sleep. (Delta waves) lower freq and higher amp.

5. Stage 5: the body is paralysed yet the brain activity closely resembles the awake brain. Produces theta waves and rapid eye movement.

What is one strength of ultradian rhythm? Hint: practical value.

1. One strength of ultradian rhythms is that it has improved the understanding of age-related changes in sleep.

2. Sleep scientists have observed that SWS reduces with age. Growth hormone is mostly produced during SWS therefore this is reduced in older people.

3. According to Cauter et al, the resulting sleep deficit may explain various issues in old age such as reduced alertness. In order to increase SWS, relaxation and medication may be used.

4. Knowledge of ultradian rhythms had practical value.

What is one limitation of ultradian rhythms? hiNT: individual differences.

1. one limitation is there is significant variation between people.

2. Tucker et al found large differences between ppts in terms of the duration of each sleep stage, particularly stage 3 and 4.

3. Tucker suggested that these difference are most likely to be biologically determined.

4. This makes it difficult to describe 'normal sleep' in any meaningful way.

What is an endogenous pacemaker?

Internal body clocks that regulate many of our biological rhythms such as the influence of SCN on sleep wake cycle.

What primary endogenous pacemaker is involved and how?

1. The suprachiasmatic nucleus is a tiny bundle of nerves cells in the hypothalamus which helps maintain circadian rhythms.

2. Nerve fibres from the eye cross at the optic chiasm on their way to the visual cortex.

3. The SCN lies just above the optic chiasm and receives information about light.

How does the SCN influence the sleep wake cycle?

1. Decoursey et al destroyed SCN connections in the brains of 30 chipmunks which were returned to their natural habitat and observed for 80 days.

2. Their sleep/wake cycle disappeared and many were killed by predators.

3. Ralph et al bred mutant hamsters with a 20 hour sleep/wake cycle. SCN cells were transplanted from the foetal tissue of these hamsters into the brain of normal hamsters, which then developed cycles of 20 hours.

How are the pineal gland and melatonin involved in our sleep-wake cycle?

1. The SCN passes information on day length to the pineal which increases production of melatonin during the night.

2. Melatonin is a hormone that induces sleep and is inhibited during periods of wakefulness.

3. Suggested as a causal factor in SAD.

What is one limitation of the endogenous pacemaker?

1. One limitation of SCN research is that it may obscure other body clocks.

2. Research has revealed that there are numerous circadian rhythms in many organs and cells in the body.

3. They are influenced by the actions of SCN but also can act independently. D

4. Damiola et al demonstrated how changing feeding patterns in mice could alter the circadian rhythm of cells in the liver by up to 12 hours, whilst SCN is unaffected.

5. tHIS SUGGESTS other complex influences on the sleep/wake cycle.

What are exogenous zeitgebers?

1. external factors that affect or entrain our biological rhythms such as influence of light in the sleep-wake cycle.

2. Without external cues, the free-running biological clocks continue to tick in a cyclical pattern.

How does light influence the sleep/wake cycle?

1. Light can reset the body's main endogenous pacemaker (SCN) also has a indirect influence on key processes such as hormone release.

2. Campbell and Murphy woke 15 ppts at various times and shone lights at the back of their knees - producing a deviation in the sleep/wake cycle of up to 3 hours.

3. Light is a powerful exogenous zeitgeber detected by the skin receptors, so it does not rely on the eyes to influence SCN.

What role do social cues have on sleep/wake cycle?

1. initially newborns sleep/wake cycle is pretty much random but at about 6 weeks, the circadian rhythm begin. Then by 16 weeks they have been entrained by schedules of the parents.

2. Research on jet lag suggests that adapting to local times for eating and sleeping is an effective way of entrainment circadian rhythms.

What is one limitation of exogenous zeitgebers? Hint: methodological issues

1. One limitation is methodological issues in exogenous zeitgebers research.

2. Campbell and mURPHY study is yet to be replicated and is criticised because there may have been some light exposure to ppts eyes - a major confounding variable.

3. Also isolating one exogenous zeitgeber in this way does not give insight into many other exogenous zeitgebers that influence the sleep/wake cycle.

4. Some studies may have ignore the way in which different exogenous zeitgeber interact.