Lessons 06 - 13

Question 1

What are the three main sections of the brain?

Answer 1

Forebrain (front part)
Midbrain (middle part)
Hindbrain (back part)

Question 2

Cerebrum

Answer 2

In the forebrain
Largest part of the brain
Split in the middle into two halves (hemispheres), which communicate via the corpus callosum
Has FOUR LOBES: frontal lobe (thought and production of speech), occipital lobe (processing of images), temporal lobe (cognitive skills), parietal lobe (sensory information)

Question 3

Diencephalon

Answer 3

In the forebrain
Located just inside the cerebrum, just above the brain stem
Responsible for SENSORY FUNCTION , food intake and the body’s SLEEP CYCLE
Divided into the thalamus, hypothalamus and epithalamus

Question 4

Cerebellum

Answer 4

In the hindbrain
Below and behind the cerebrum and attached to the brain stem
Controls MOTOR FUNCTION, BALANCE, and ability to interpret information sent to the brain by the senses

Question 5

Brain stem

Answer 5

In the midbrain and hindbrain
Governs BLOOD PRESSURE , some reflexes, ‘fight and flight’, breathing, heartbeat
Motor and sensory neurons travel through the brain stem, allowing impulses to pass between the brain and spinal cord

Question 6

Localisation of function

Answer 6

Refers to the principle that SPECIFIC FUNCTIONS HAVE SPECIFIC LOACTIONS in the brain
Franz Gall proposed ‘PHRENOLOGY’, the theory that the bumps on the skull determined personality. He said that functions were localised to specific regions - the opposing view is that the brain functions holistically, with all or large parts involved in all behaviours
Broca’s case studies on brain-damaged patients concluded that speech production was localised in an area in the frontal lobe (Broca’s area)

Question 7

Somatosensory cortex

Answer 7

Receives SENSORY INPUT FROM RECEPTORS in the skin (touch, pain, pressure, temperature)
In the PARIETAL lobe
Hands and face take up over half of the somatosensory area

Question 8

Motor cortex

Answer 8

Responsible for VOLUNTARY MOVEMENTS
In the back of the FRONTAL lobe
Both hemispheres have one (motor cortex on one side of the brain controls the opposite side of the body)
Different parts of the motor cortex control different parts of the body

Question 9

Visual centre

Answer 9

Primary visual centre is in the OCCIPITAL lobe
It deals with VISUAL PERCEPTION, and requires additional processing in neighbouring cortical areas - these areas are where sensation is converted into perception. Damage to these areas leads to a loss of specific aspects of visual perception. Prosopagnosia (loss of ability to recognise faces), achromatoposia (loss of ability to see in colour)

Question 10

Auditory centre

Answer 10

Concerned with HEARING
Mostly lies within the TEMPORAL lobes in both the left and right hemispheres
The auditory pathways begin in the inner ear, where sound waves are connected to nerve impulses, which travel via auditory nerve to the auditory cortex

Question 11

Language centres

Answer 11

• Broca’s area:
  Speech PRODUCTION
  Paul Broca studied patients who could understand language but could not speak or put their thoughts into writing. They had lesions in their left frontal hemisphere.
  Posterior portion of the frontal lobe of the left hemisphere
  Damage = Broca’s aphasia / expressive aphasia
• Wernicke’s area:
  Speech PERCEPTION
  Posterior left temporal lobe
  Damage = Wernicke’s aphasia / receptive aphasia

There is a NEURAL LOOP, arcuate fasciculus, running between Broca’s area and Wernicke’s area

Question 12

Evaluation of localisation of function

Answer 12

+ BRAIN SCAN EVIDENCE suggests neurological functions are localised (esp. language and memory). Peterson et al. (1988) used brain scans to show that Wernicke’s area was active during a listening task, and Broca’s area was active during a reading task. Brain scans are scientific evidence, so increase the validity
+ NEUROSURGICAL EVIDENCE: Dougherty et al. (2002) reported on 44 OCD patients who had undergone brain surgery. After 32 weeks, 1/3 of them had recovered from the symptoms; shows how mental disorders are localised
+ CASE STUDY evidence: Phineas Gage - change in personality after damage to frontal lobe
+ APHASIA STUDIES : damage to Broca’s area results in expressive aphasia, damage to Wernicke’s area results in receptive aphasia
- REDUCTIONIST: Lashley removed parts of rats’ brains and found that no area was more important in terms of the rats ability to run a maze - not localised to only one area
- PLASTICITY: the brain can reorganise itself and compensate for the lost function
- INDIVIDUAL DIFFERENCES: case studies and also women have a proportionally larger Broca’s area than men. Not able to generalise

Question 13

Phineas Gage

Answer 13

1848: an explosion resulted in a metal pole passing behind his left eye and exiting his skull. He survived but his FRONTAL lobe was damaged. His personality was changed (calm to quick-tempered and rude)

Question 14

Brain lateralisation

Answer 14

The idea that the TWO HALVES of the brain are NOT exactly ALIKE. Research has shown that the left hemisphere is dominant for language and the right hemisphere with visual-motor tasks. The two hemispheres are connected by the corpus callosum.
LEFT = LANGUAGE
RIGHT = VISUAL MOTOR

Question 15

Evaluation of brain lateralisation

Answer 15

(+) Helps to understand more about MULTI-TASKING. Lateralisation allows the other hemisphere to engage in a different task. Rogers et al. (2004) found that in the domestic chicken, brain lateralisation is used to find food, and also to be vigilant for predators. It increases brain efficiency
(+) Can study LEFT-HANDEDNESS (people who have right hemispheric dominance) and why they are prone to allergies and illness. Tonnessen et al. (1993) found a small but significant link between handedness and immune disorders
(-) Lateralisation changes with AGE. Szaflarski et al. (2006) found that language became more lateralised to the left hemisphere until 25, but decreased after that. We should be cautious assuming that brain lateralisation is set in stone
(-) Does not explain brain PLASTICITY. It can take over and do the job of both hemispheres, and can potential limitations associated with lateralisation

Question 16

Split-brain research (to support brain lateralisation)

Answer 16

AKA commissurotomized
Patients who suffer from epilepsy had an operation where their CORPUS CALLOSUM was cut, severing the communication between the two hemispheres. This helped to study whether one hemisphere is more dominant in controlling certain characteristics

Question 17

Split-brain research: Sperry and Gazzaniga (1967)

Answer 17

The hemispheres could not communicate (corpus callosum was cut)
The left side of the body is controlled by the right hemisphere and vice versa
METHOD: They would send visual information to just one hemisphere at a time to see what types of information is processed specifically by each hemisphere.
An image/word is projected to the patient’s left visual field (right hemisphere) or the right visual field (left hemisphere).
Three tasks: describe what you see, tactile test (an object in one hand, describe that they felt), drawing task
FINDINGS: In the describe test, picture presented to the right visual field (left hemisphere) could be described verbally. Left visual field, could not describe.
In the tactile test, objects in right hand (left hemisphere) were described verbally. Left hand, could not describe
In the drawing task, the picture was clearest and best when presented to the left visual field (right hemisphere)
CONCLUSION: The LEFT hemisphere is dominant in terms of speech and LANGUAGE. The RIGHT hemisphere is dominant in terms of VISUAL-MOTOR tasks

Question 18

Split-brain research: Turk et al. (2002)

Answer 18

Interested in face processing after split-brain surgery. Patient was JW. The stimuli were morphed faces, one face was JW’s, the other was one of the researchers who he worked with for many years. The morphs were created from 0% (100% familiar face) to 50/50 (JW and familiar face) to 100% (100% JW). The researchers used the divided field procedure to present to each hemisphere separately
In one set of trials, he would press a button if the image was himself, and in another, he would press the button if the image was the other person
The right hemisphere had a clear bias towards identifying the familiar face, the left hemisphere has a clear bias towards identifying himself
The RIGHT hemisphere is better at FACE-PROCESSING, the LEFT hemisphere is better at SELF-RECOGNITION

Question 19

Evaluation of split-brain research

Answer 19

(+) Can PROVE hemispheric LATERALISATION and that each has a different function (left = speech and language, can break information down, right = video-spatial processing and facial recognition, holistic processor)
(+) RESEARCH support - Sperry’s studies. Also tells us about normal brain functioning and that the connectivity between the different areas is as important as the function of one
(-) Has not shown that the brain is ORGANISED into DIFFERENT areas with specific sections responsible for specific tasks
(-) SAMPLE in Sperry’s research (small sample size, extremely varied group who differ in age, gender and handedness)
(-) Operations were NOT always COMPARABLE because in some cases, not all pathways connecting both hemispheres were always cut

Question 20

Plasticity

Answer 20

The ability of the brain to change and ADAPT in light of various experiences, either positive (learning, memory) or negative (brain damage)
The first year of a baby’s life is the most important to study plasticity. The brain has more neurons and synapses. If a whole hemisphere is removed soon after birth, the baby grows up showing very few impairments (example of plasticity).
Study with Tibetan monks - meditation changes the workings of the brain in the short term and may also produce permanent changes (the monks had more gamma wave activity than the control group)

Question 21

Evaluation of plasticity

Answer 21

(+) RESEARCH support from ANIMAL studies: Kempermann et al. (1998) found more neurons in rats housed in complex homes than in rats housed in ordinary cages. Blakemore and Mitchell (1973) found that kittens reared in an environment with black vertical stripes did not respond to horizontal black stripes (exposure to certain stimuli affects brain development). BUT may not be generalised to humans
(+) RESEARCH support from HUMAN studies: Maguire et al. (2000) found that taxi drivers had larger front parts of the hippocampus compared to a control group and this was positively correlated to how long they had spent in their jobs
(-) ETHICAL ISSUES : consent and protection from harm (especially with babies). Hard to know what babies are thinking. Animal studies cannot be generalised to humans (kittens are mobile from birth, babies aren’t)
(-) AGE differences with plasticity. It is thought that brain plasticity reduces with age, but older people can learn new skills

Question 22

Functional recovery after brain trauma

Answer 22

The TRANSFER OF FUNCTIONS from a damaged area of the brain to undamaged areas. Traumatic brain damage can affect all areas of behaviour. In the 1960s, researchers studied stroke victims who were able to regain functioning. When brain cells were damaged, the brain REWIRES itself so some level of function can be regained.

Question 23

Mechanisms for recovery

Answer 23

The brain is able to rewire itself through multiple structural changes:
AXONAL SPROUTING : the growth of new nerve endings that connect with undamaged nerve cells to form new neural pathways
DENERVATION SUPERSENSITIVITY: axons become aroused to a higher level to compensate
RECRUITMENT of homologous (similar) areas on the opposite side of the brain

Question 24

Evaluation of functional recovery after trauma

Answer 24

PRACTICAL applications: functional recovery processes have contributed to the field of neurorehabilitation. This can help doctors provide therapy

AGE differences: the commonly accepted view is that functional recovery after brain trauma reduces with age. However, studies show that abilities can still be modified in adults. The capacity for neural reorganisation is much greater in children than in adults

EDUCATIONAL attainment: patients with the equivalent of a college degree were 7x more likely to recover from severe brain trauma. The longer time spent in education had a direct relationship with functional recovery. Therefore we should encourage the younger generation to complete their education

Question 25

Ways of studying the brain

Answer 25

fMRIs, EEGs, ERPs, Post Mortems
The first method was the CT scan. It used X-Rays to take images of brain structures, and could identify major structures or abnormalities.
The CT scanner was replaced by the MRI, that used strong magnetic field and radio waves to produce highly detailed images.
The PET scan used a radiative substance (e.g. glucose), which was injected into the blood stream and travelled to the brain. Neurons use glucose as an energy source, so the more active areas would accumulate more glucose; the radioactivity was picked up the PET scan. But this was invasive and prolonged

Question 26

Functional magnetic resonance imaging (fMRI)

Answer 26

Neurons most active during a task use more energy, requiring glucose and oxygen to be carried in the bloodstream. Blood flow to active areas increases. fMRI scans measure BLOOD FLOW through the concentration of oxygen in the blood stream, using the BOLD contrast (Blood Oxygen Level Dependent).
Applications include lie detection - it is very difficult to fake blood flow

Question 27

Evaluation of fMRIs

Answer 27

(+) Does not rely on radiation. It is non-invasive and virtually risk-free (all the participant needs to do is remain still and quiet in the scanner). More people can participate
(+) Good spatial resolution (1-2mm) - ability to detect small features. Better than other techniques. This allows psychologists to discriminate between different brain regions with greater accuracy
(-) Impossible to infer causation, as fMRIs do not provide a direct measure of neural activity. Blood flow shows activity in certain areas, but not whether the region is associated with a particular function
(-) Poor temporal resolution (1-4 seconds) - the accuracy in relation to time/how quickly changes in brain activity can be detected. Worse than other techniques (which are 1-10 milliseconds). A lag with the scan
(-) Cannot show the activity of individual neurons, so does not provide a complete picture

Question 28

Electroencephalogram (EEG)

Answer 28

A large number of small recording electrodes are distributed over the skull. These pick up the electrical activity of neurons. It can detect various types of brain disorders. It measures amplitude (size of intensity) and frequency (speed or rapidity) of the electrical activity.
Two distinct states: synchronised pattern (recognisable waveform) and desynchronised pattern (no recognisable waveform).
Different types of waves: alpha, beta, delta, theta.
EEG is useful in identifying the general state of the brain and has been used to study sleep

Question 29

Evaluation of EEGs

Answer 29

(+) Provides recordings of the brain in REAL TIME rather than a still image, so activities can be accurately measured
(+) Provides invaluable DIAGNOSIS of conditions (e.g. epilepsy). Has contributed to our understanding of the stages involved in sleep
(-) Cannot reveal what is happening in deeper regions, it can only detect activity in SUPERFICIAL regions
(-) Not useful for pinpointing the EXACT SOURCE of neural activity

Question 30

Event related potentials (ERPs)

Answer 30

Small voltage changes in the brain that are triggered by stimuli. Uses a similar array of recording electrodes as the EEG, the difference is that a stimuli is presented (many times because it is difficult to separate that electrical activity and the brain’s overall activity), and the psychologist is looking for specific electrical responses. Doing it multiple times means the responses add up gradually allowing the event related potential to emerge

Question 31

How do ERPs work?

Answer 31

Electrodes are placed on the person’s head. They are presented with a sequence of stimuli and a recording of the brain’s electrical impulses is taken. The person is presented with one familiar stimulus and four unfamiliar ones. Each stimuli is repeated 30 times, so there are (30 x 5 =) 150 trials. The ERPs summate the reactions to each stimuli, and there will be a difference between the familiar and unfamiliar stimuli.
Upward spikes are known as positive waves, downwards, negative

Question 32

Evaluation of ERPs

Answer 32

(+) Short latency (interval between stimulus presentation and the beginning of the ERP). Means that ERPs can reflect the early stages of cognitive processing
(+) Possible to monitor covertly the processing of a particular stimulus, no behavioural response needed.
(-) Poor spatial localisation. It is possible to localise components of the ERP to general areas of the cortex, but not possible to localise ERPs components to specific areas of the cortex
(-) Lack of standardisation between research studies, so findings cannot be confirmed, or generalised. Extraneous variables must be minimised to collect the correct data, but this is not always possible in reality

Question 33

Post-Mortem Examinations

Answer 33

AKA autopsies
A researcher may study a person’s brain when they are alive, and then compare it after death to look for abnormalities. Examples would be Broca and Wernicke, who eventually discovered the regions named after them.
Post-mortems have successfully contributed to the understanding of many disorders. Iverson found that schizophrenics have a higher concentration of dopamine compared to people without.
They also allow for a more detailed examination of anatomical and neurochemical aspects, and of deeper regions (hypothalamus etc.), both of which are not possible with other methods of investigation

Question 34

Evaluation of post-mortem examinations

Answer 34

(+) Allow for more detailed examinations of the anatomical and neurochemical aspects that would not be possible through other methods. It enables researchers to examine deeper regions of the brain (hypothalamus, hippocampus etc.)
(+) Harrison (2000) said that post-mortems have played a central part in our understandings of schizophrenia and other mental illnesses. Iverson found a higher concentration of dopamine in the limbic system of schizophrenia patients.
(-) Too many individual differences (how people die, the length of time between death and autopsy, drug treatments, age of death etc.). This means findings cannot be generalised
(-) Ethical issues in relation to informed consent, and whether or not a patients consents before death. Also, many post-mortems are done on patients with psychological deficits, so they would be unable to provide fully informed consent
(-) Post-mortem research is limited as it is retrospective. The person is dead, so follow ups cannot be made

Question 35

Biological rhythms - Circadian rhythms

Answer 35

24 hours
Reset by levels of light
Nearly all organisms possess a biological representation of the 24 hour day
Circadian rhythms are driven by the suprachiasmatic nuclei (SCN) in the hypothalamus. It is constantly reset so our bodies are in synchrony with the outside world. Natural light sets out body clock in a process called photoentrainment

Question 36

Circadian rhythms - Sleep wake cycle

Answer 36

Light and darkness are the external signals that determine when to sleep and wake up. The strongest sleep drive occurs between 2-4 am, and 1-3 pm
Sleep and wakefulness are under homeostatic control. This homeostatic drive increases gradually throughout the day. The internal circadian clock will maintain a cycle of 24-25 hours
Michel Siffre spent long periods of time underground, with no external cues (no daylight, clocks, radio). His natural circadian rhythm settles to 24-25 hours, but would sometimes dramatically change to 48 hours. As he got older, his internal clock ticked more slowly, and his sleeping patterns changed.

Question 37

Circadian rhythms - Core body temperature

Answer 37

Core body temperature is at its lowest (36°C) at 4:30 am and highest (38°C) at 6pm. Sleep occurs when the core temperature begins to drop, and wakefulness occurs when the temperature begins to rise
Folkard et al. (1977) found that children who had stories read to them at 3pm showed better recall than children who had stories read to them at 9am, supporting core body temperature
Gupta (1991) found improved IQ performance when participants were assessed at 7pm compared to 2pm and 9pm. There is a small drop in body temperature between 2-4pm, which could explain Gupta’s findings

Question 38

Circadian rhythms - Hormone production

Answer 38

The release of melatonin from the pineal gland is at its peak during hours of darkness. Melatonin encourages sleep (by activating chemical receptors in the brain). When it is light again, the production of melatonin drops.

Question 39

Evaluation of Circadian rhythms

Answer 39

(+) Practical applications - chronotherapeutics (the study of how timing affects drug treatments). For example: the risk of heart attack is greatest during the early morning hours, so medication should be taken before sleep, so they are released at 6am
(+) Better understanding of the consequences of disrupting circadian rhythms. People doing shift work experience reduced concentration at 6am, which means it is more likely for mistakes to occur. Employers can use this to make sure people are not busy then
(-) Uses case studies and small sample sizes (Michel Siffre) means it can not be generalised, not representative
(-) Early research studies deprived people of objects (e.g. clocks), but not of artificial light. However, Czeisler et al. (1999) manipulated artificial lighting and altered circadian rhythms to 22-28 hours, suggesting circadian rhythms may not be so timely

Question 40

Biological rhythms - Ultradian rhythms

Answer 40

Last fewer than 24 hours
Can be found in the pattern of human sleep (4 stages of NREM and 1 stage of REM). It repeats every 90 minutes
Stages 1 and 2: ‘light sleep’, alpha and theta waves
Stages 3 and 4: ‘deep sleep’, delta waves
Stage 5: REM, paralysis, beta waves
Kleitman (1969) referred to the 90 minute cycle as the Basic Rest Activity Cycle (BRAC). He said the cycle continues when we are awake, so we move from a state of alertness into fatigue etc.
Dement and Kleitman (1957) did a study of the brain activity of 9 people (7 males and 2 females) in a sleep lab. Alcohol and caffeine were controlled. Distinct patterns during each sleep stage in EEG patterns were reported. REM sleep was highly correlated with dreaming.

Question 41

Evaluation of ultradian rhythms

Answer 41

(+) Research support for Dement and Kleitman for stages of sleep, reliable and ultradian rhythms do occur
(+) Ericsson et al. (2006) found support for BRAC. Violinists has practice sessions limited to 90 minutes. The best violinists nap more. The same pattern was found with musicians, athletes, chess players and writers
(-) Individual differences, so cannot generalise. Tucker et al. (2007) suggests that there are individual differences in sleep patterns that are biologically determined and may be genetic. Researchers have found differences in sleep duration, time to fall asleep and the amount of sleep in each stage, suggesting differences

Question 42

Infradian rhythms - the menstrual cycle

Answer 42

Infradian rhythms span a period longer than 24 hours (maybe weeks, months, a year)
Menstrual cycle is usually around 28 days
Regulated by hormones (oestrogen, progesterone, LH, FSH). Ovulation occurs halfway through the cycle, when oestrogen levels are highest. Then progesterone levels increase in preparation for the embryo
Is an endogenous system, but evidence suggests it may be influenced by exogenous factors, such as the cycle of other women

Question 43

Evaluation of Infradian rhythms - the menstrual cycle

Answer 43

(+) Research suggests it is influenced by exogenous zeitgebers. Reinburg (1967) examined a woman who spent 3 months in a cave with a small lamp for light, and noticed her cycle shortened to 25.7 days, suggesting the lack of light influenced her cycle
(+) Research suggests it is influenced by exogenous zeitgebers. Russell et al. (1980) saw synchronised cycles through odour exposure. Sweat samples from one group of women were rubbed on the upper lips of other women, and their cycles synchronised, suggesting synchronisation can be affected by pheromones.
(+) The synchronised cycle provides an evolutionary advantage for groups of women; synchronisation of pregnancies meant that childcare could be shared
(+) Infradian rhythms are important regulators of behaviour. Penton-Volk et al. (1999) found that women preferred feminised faces at the least fertile stage of their menstrual cycle, and a more masculine face at the most fertile. Women’s sexual behaviour is motivated by infradian rhythms.
(-) Methodological limitations. There are many possible factors (stress, diet, exercise), that can act as confounding variables.

Question 44

Infradian rhythms - SAD (seasonal affective disorder)

Answer 44

Seasonal variation in mood, where people are depressed during winter
Infradian rhythm governed by a yearly cycle
Melatonin, secreted by the pineal gland, is partially responsible because the lack of light in winter means a longer period of melatonin secretion, which is linked to depressive symptoms

Question 45

Evaluation of Infradian rhythms - SAD

Answer 45

(+) Terman (1988) found the rate of SAD is more common in Northern countries, where winter nights are longer: 10% in New Hampshire (northern), and 2% in Florida (southern)
(+) Practical applications. Treatments for SAD include phototherapy, a lightbox that simulates strong light, resetting melatonin levels, regulating serotonin levels, and improves symptoms
(-) The lightbox study is flawed, because 30% of participants showed improvement when treated with a placebo

Question 46

Endogenous pacemakers

Answer 46

The body’s internal biological clock
The most important is the superchiasmatic nuclei (SCN), a cluster of nerve cells in the hypothalamus. It is the master clock that links other brain regions and has control over other biological clocks.
Neurons within the SCN synchronise with each other, so the target neurons receive time-coordinated signals
The SCN regulates the manufacture and secretion of melatonin in the pineal gland via the interconnecting neural pathway (melatonin encourages sleep)

Question 47

Evaluation of endogenous pacemakers

Answer 47

(+) The SCN is of vital importance. Morgan (1995) bred hamsters that had circadian rhythms of 20 hours. SCN neurons from these hamsters were transferred to normal hamsters, and they displayed the abnormal circadian rhythm of 20 hours. Shows importance of endogenous pacemakers
(+) Folkard (1996) studied a student who spend 25 days in a laboratory without daylight or other exogenous zeitgebers. her core temperature rhythm was still 24 hours. Shows importance of endogenous pacemakers
(-) Many studies are unethical (breeding hamsters etc.). It is also not ecologically valid as people don’t have their circadian rhythms deliberately tampered with
(-) Folkard (1996) found that the student’s sleep wake cycle had extended to 30 hours, suggesting exogenous zeitgebers are important too

Question 48

Exogenous zeitgebers

Answer 48

External cues (environmental events) that help regulate the internal biological clocks.
LIGHT: Receptors in the SCN are sensitive to changes in light, which resets the internal biological clock, keeping it on a 24 hour cycle. Melanopsin (protein in the retina) is critical in this system. When moving to night shift, or travelling, the endogenous pacemakers are out of synchrony with the exogenous zeitgebers, leading to increased anxiety, disturbed sleep patterns and decreased alertness (jet lag)
SOCIAL CUES: Meal times and activities can act as zeitgebers, and can compensate for the absence of natural light. With infants, their parents impose mealtimes and bedtimes, showing how exogenous zeitgebers can effect the sleep wake cycle

Question 49

Evaluation of exogenous zeitgebers

Answer 49

(+) Studies of blind people. Skene and Arendt (2007) estimate that the majority of blind people who still have light perception have normal circadian rhythms. This suggests that exogenous zeitgebers are important in the sleep wake cycle
(+) Light exposure can be used to avoid jet lag. Light exposure keeps people awake (less melatonin). This shows an important application of exogenous zeitgebers
(-) Not all studies support the influence of light on the sleep wake cycle. Vetter et al. (2011) studied two groups, one who remained in normal warm artificial light, while the others experienced artificial blue light. Participants under the warm light synchronised their rhythms to the natural light of dawn. Participants under blue light synchronised their patterns to office hours. This study suggests that the shade of light is an important influence on the sleep wake cycle. Natural light is a more influential exogenous zeitgeber