Biopsychology - Paper 2
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95 Terms
The nervous system
Highly specialised cells.
Primary internal communication.
Made - lots of neurons.
Nervous system - peripheral nervous system (PNS) and central nervous system (CNS).
The central nervous system
Brain = in all psychological processes, main job = life is maintained, brain stem = used in breathing and vital functioning, prefrontal cortex = higher order thinking, function 1 = collect, process and respond to information, function 2 = coordinate and direct how other organs work.
Spinal cord = carries messages via neurons to and from brain to PNS, allows brain to monitor bodily processes (breathing and digestion), main centre for reflex actions/ arc.
The peripheral nervous system:
Includes - all nerves in the body outside the brain and spinal cord.
Function - relay nerve impulses from CNS to the body.
12 pairs of cranial nerves (under the brain) and 30 pairs of spinal nerves (connected to spinal cord).
Somatic nervous system
Motor and sensory neurons. |
Controls voluntary movement like moving skeletal muscles and bones. |
Control centre - motor cortex and somatosensory cortex. |
1st component - sensory pathway transmits and receives information from the senses (visual to eyes) |
2nd component - motor pathway directs voluntary movement of skeletal muscles which orchestrates all movements from the brain. |
Conscious |
Autonomic nervous system
Motor neurons. |
Controls involuntary movement of internal organs and glands to sustain processes like heartbeat and breathing. |
Control centre - hypothalamus. |
Sympathetic branch - switches fight and flight on. |
Parasympathetic branch - switches rest and digest on. |
unconscious |
Neurons and synaptic transmission
Neurons - relay information around the brain the NS, uses electrical impulses and neurotransmitters.
Structure of a neuron
Dendrites - receives nerve impulses.
Cell body/ soma - protects nucleus.
Nucleus - control centre and contains DNA/ chromosomes.
Axon - signal passes on.
Myelin sheath - insulates and speeds up transmission.
Nodes of ranvier - speeds transmission.
Axon terminals/ terminal buttons - releases signal to the next cell.
Process of synaptic transmission
Dendrite picks up neurotransmitters.
Sends electrical impulse (action potential) through the cell body, along the axon and to terminal buttons.
Synaptic vesicles contain and store neurotransmitters.
Converts electrical impulse to chemical.
Impulse reaches synaptic vesicles and releases neurotransmitters.
Crosses synaptic gap by diffusion.
Binds to specialised receptors on the surface of the next cell (dendrites).
Next cell activates to produce either an inhibitory (GABA) or excitatory (serotonin) at a postsynaptic level.
Reuptake happens where neurotransmitters that are not used are recycled by presynaptic neurons.
Synaptic transmission is complete.
Endocrine system
Function - secretes hormones in the bloodstream that regulates many body functions.
Provides a chemical system of communication via bloodstream.
Network of glands that secrete hormones.
Hormones - chemical messengers that circulate throughout the blood.
Pituitary gland = growth hormone (promotes cell growth).
Pineal gland = melatonin (biological rhythms like sleep).
Thyroid gland = thyroxine (regulates metabolism).
Ovaries = oestrogen (controls female reproductive system).
Body’s response to stress
autonomic nervous system - sympathetic branch.
Short term stressors (like slamming on the brakes) - SAM system activated.
Chronic stressors (like being unhappy in a relationship) - pituitary adrenal system (HPA Axis) activated.
Fight or flight response
Hippocampus and amygdala recognises emotional reaction to stimuli.
If potentially stressful, a message sent to hypothalamus.
Hypothalamus recognise acute stressor.
Sympathomedullary (SAM) pathway activated (the sympathetic branch).
Stimulates adrenal glands, stimulates adrenal medulla, releases adrenaline and noradrenaline.
Releases the adrenaline hormone into the blood.
Parasympathetic branch
Constrict pupils |
Slows heartbeat |
Constrict airways |
Stimulate stomach activity |
No perspiration |
Sympathetic branch
Dilate pupils (improves vision) |
Increases heartbeat (increases oxygenated blood to muscles and transports adrenaline faster) |
Relax airways (increased breathing for increased oxygen intake) |
Inhibit stomach activity (saves energy for fighting or fleeing) |
Increased perspiration (regulates body temperature and cools individuals done quicker) |
Ways of studying the brain
Post-mortem
fMRI
EEG’s
ERP’s
Post-mortem
After death examinations.
Correlates structural abnormalities to behaviour changes.
Sliced into thin sections and studied under a microscope.
Strengths of post-mortem
Allows detailed examination of the different structures in the brain.
Can access hippocampus and hypothalamus that scanning techniques can not.
Weaknesses of post-mortem
When oxygen is cut off the brain shape and structure changes.
Issue of causation (problem in life time might not be linked to the deficits around the brain).
fMRI
Functional magnetic resonance imaging.
Uses a magnetic field and radio waves.
Detects the changes in blood oxygenation in the brain.
Shows where there is high activity.
Strengths of fMRI
Provides a moving image of brain activity.
Good spatial resolution (able to distinguish between different brain areas).
Weaknesses of fMRI
Only focuses on localisation of activity not the communication between different brain areas.
Poor temporal resolution (takes 1 to 4 seconds so does not correlate to the speed it happens at in real life).
EEG’s
Electroencephalograms.
Uses electrodes fixed to the scalp to identify neural activity.
Recording of brain activity.
Strengths of EEG’s
Good temporal resolution (happens in real life time).
Cheaper method so large samples can be used.
Weaknesses of EEG’s
Poor spatial resolution (can not identity activity in deeper parts of the brain like hypothalamus).
Signals can be detected by many electrodes so we can not pinpoint the activity.
ERP’s
Event related potentials.
Uses electrodes attached to the scalp.
Presents a stimulus and a neural response is looked for.
Strengths of ERP’s
Gives the earliest indication of conscious cognitive processing.
Good temporal resolution
Weaknesses of ERP’s
Electrical activity deep in the brain is not recorded.
Poor spatial awareness.
Similarities between fMRI and EEG’s
Ethical - full consent needed.
Non-invasive - not uncomfortable.
Based on interpretation - by experts.
Not causation clear - no direct neural activity.
Differences between fMRI and EEG’s
fMRI - good spatial resolution.
EEG’s - bad spatial resolution.
fMRI - bad temporal resolution.
EEG’s - good temporal resolution.
fMRI - stimulus presented.
EEG’s - no stimulus presented.
Similarities between fMRI and ERP’s
Ethical - informed consent needed.
Non-invasive - not uncomfortable.
Based on interpretation.
Based on stimulus presentation.
Differences between fMRI and ERP’s
fMRI - good spatial resolution.
ERPs - bad spatial resolution.
fMRI - bad temporal resolution.
ERPs - good temporal resolution.
fMRI - not causation clear.
ERPs - causation clear.
fMRI - high cost.
ERPs - low cost.
Similarities between ERP’s and EEG’s
Ethical - informed consent needed.
Good temporal resolution.
Bad spatial resolution.
Low cost.
Non-invasive.
Based on interpretation.
Differences between ERP’s and EEG’s
EEG’s - not causation clear.
ERPs - causation clear.
EEG’s - no stimulus presented.
ERPs - stimulus presented.
Similarities between post-mortem and scanning techniques
Based on interpretation.
Can be a high cost.
Ethical - informed consent is needed.
Differences between post-mortems and scanning techniques
PM - no spatial resolution.
Others - spatial resolution.
PM - no temporal resolution.
Others - temporal resolution.
PM - invasive.
Others - non-invasive.
PM - not causation clear.
Others - can be causation clear.
PM - stimulus not presented.
Others - some present a stimulus.
Localisation of function in the brain
Localisation - theory where specific areas of the brain are associated with particular physical and psychological functions.
Cerebral cortex - outer layer of the brain, made up of left and right hemispheres, connected by corpus callosum (allows communication between both hemispheres).
Frontal lobe - motor cortex, aware of what we are doing in our environment, personality.
Parietal lobe - somatosensory cortex, sensory perception.
Occipital lobe - visual cortex, vision.
Temporal lobe - auditory cortex, hearing ability.
Wernicke’s area - understanding language.
Broca’s area - producing language.
Contralateral - right controls left and left controls right.
Somatotopically - smaller areas are controlled by bigger portions whilst larger areas are controlled by smaller portions.
Motor cortex
Location - both hemispheres in the frontal lobe.
Role - voluntary movement, personality.
Organised - contralateral and somatotopically.
Somatosensory cortex
Location - both hemispheres in the parietal lobe.
Role - detects sensory events, production of sensations.
Organised - contralateral and somatotopically.
Visual cortex
Location - back of the brain in the occipital lobe.
Role - light enters retina, strikes photoreceptors, nerve impulses transmits to optic nerve.
Organised - contralateral.
Auditory cortex
Location - near the ears of both hemispheres in the temporal lobe.
Role - hearing, cochlea sends sound waves to nerve impulses, travels to the brain stem for decoding.
Organised - contralateral.
Strength of localisation of function in the brain
Miller’s case study of HM:
The hippocampus in the temporal lobes was removed to try and help his epilepsy.
He could remember long term but could not make new ones.
Adds credibility and validity as when certain areas were damaged the function was lost like memory.
Strength of localisation of function in the brain
Case study of Phineas Gauge:
He was working on railroads when an explosion happened.
1 metre iron rod through left cheek out of the top of his head.
The left frontal lobe was damaged, changed from calm to lacking social inhibition and self-control.
Shows how personality, emotional processing and decision making is localised in the prefrontal lobe.
Weakness of localisation of function in the brain
Contradicting research:
Lashley trained rats to run a maze to find food where he had removed 10% to 50% of their hippocampus.
Their memory of the maze was affected by how much hippocampus was removed.
Law of equipotentiality states the brain reorganises itself to recover lost function
Questions localisation as other regions can take over specific functions following brain injury.
Weakness of localisation of function in the brain
The research supporting is a case study:
Patient ‘Tan’ and HM.
Both are unique experiences that are hard to generalise as experiences may not apply to all individuals.
Results may not fully support theory and damage may be specific so it is difficult to understand.
Hemispheric lateralisation
Where specific brain functions are found only in one hemisphere.
Left hemisphere - focuses on detail, active = asked to identify small detail, meths, reasoning, language, examples = speaking at meetings, writing reports.
Right hemisphere - processes overall patterns, active = asked to make sense of something, spatial relationships = finding your way and remembering a route, recognition of emotions = identifying the feelings of others.
Language centres - language is lateralised to the left hemisphere.
Broca’s area
Discovered - Broca found patients who had language production issues but not language speed comprehension issues, studied patients, performed post-mortem after they passed, example - patient ‘Tan’.
Location - posterior (back portion) of left frontal lobe, next to the lower part of the motor cortex.
Role - coordinate speech production.
Damaged - lesions can lead to Broca’s aphasia, difficulty with speech production, not all words are equally affected (nouns + verbs = fine, conjunctions + prepositions = problems, example = reads ‘to be or not to be’ as ‘two bee oar knot two bee’.
Wernicke’s area
Discovered - observed patients with damaged posterior temporal lobes, noticed how a stroke patient could not understand written words but could hear and speak, found a lesion in the rear parietal/ temporal area of the left hemisphere near the auditory region.
Location - posterior area of the temporal lobe.
Role - comprehension of speech.
Damaged - Wernicke’s aphasia, could speak but could not understand what was said to them, caused difficulty speaking in coherent sentences or understanding others.
Neural loop (Arcuate Fasciculus)
Neural loop that runs from Broca’s area to and from Wernicke’s area.
Damage to both areas - can cause global aphasia (can not understand or produce speech).
Strength of hemispheric lateralisation
Research evidence (Broca’s case study of ‘Tan’):
They had damage in an area of the left temporal lobe in the left hemisphere.
Meaning they could not produce speech which shows the importance of this specific area for language production.
Adds credibility that specific functions are lateralised.
Contradicting point - case study = not generalisable, unique experiences, can not apply to everyone, affects everyone in a different way.
Weakness of hemispheric lateralisation
Contradicting research (Dick and Tremblay):
They found that 2% of modern researchers believe language is fully controlled in Broca’s and Wernicke’s area, and advances in brain imaging techniques (FMRI) allows for neural processes to also be studied in detail.
Language streams have been found across the cortex (regions in the right hemisphere + subcortical areas like the thalamus).
Language is not confined to specific areas and is organised more holistically, contradicting lateralisation.
Strength of hemispheric lateralisation
Experimental research (split brain research):
Sperry studied epileptic patients who had surgery to cut their corpus callosum which stopped communication between the two hemispheres.
Pts were told to describe an apple image when shown for 1/10th of a second to either left visual field or right visual field.
Findings shown on LVF could not say what it was but shown on RVF they could say what it was.
This means the brain is contralateral.
Left is geared to analytic and verbal tasks.
Right is spatial tasks and creativity.
Two hemispheres have different functions which adds validity to claims of lateralisation.
Weakness of hemispheric lateralisation
Post mortems were used:
Investigates the brain after death which is useful to pinpoint areas involved in different functions but not useful as you can not get the patient to refine understanding by completing tasks.
The brain changes size and shape as oxygen is cut off.
The patient is not alive so we are unable to conduct live tests which means causation is unclear.
Not fully understanding or relying on findings if post mortem was used as it lacks credibility.
Other imaging techniques might reveal detailed and valuable information.
Split brain research
Used to help treat epilepsy - reduces epileptic seizures to one hemisphere.
Corpus callosum - connects the two hemispheres together.
SBR - cuts corpus callosum.
Normal brain - two hemispheres share information.
Split brain - two hemispheres do not share information.
So if the visual field is restricted - differences between the functioning of the left and right hemispheres are seen.
Uses split visual field experiments.
Procedure - pts were asked to sit facing a screen and to stare at a fixed point in the centre, visual stimuli shown to one visual field at a time.
Strength of split brain research
Practical applications:
Knowledge of the left hemisphere controls language.
Target therapy to the left to help aphasia + effective treatment to become more productive.
Allows for successful rehabilitation goals.
Weakness of split brain research
Contradicting research (case study of Kim Peek + Turn):
Born with no corpus callosum but able to read out loud from a book from the right and the left pages at the same time.
If language is lateralised in the left then he could only read right pages.
Found a patient who had damage to the left hemisphere and they had developed the capacity to speak from the right hemisphere.
By functional recovery lateralised sides may appear on opposing sides after injury.
Strength of split brain research
High reliability:
All pts sat facing a screen, all stared at a fixed point in the centre, all saw the same image, all felt the same object, all given 1/10th of a second.
Standardised procedures.
Applies the concept of replicability.
If repeated by another researcher and they get similar results this increases validity and credibility.
Weakness of split brain research
Low generalisibility:
Pts varied in age, gender, age developed epilepsy and degree of drug therapy received beforehand.
All factors may affect behaviour.
Low ecological validity.
Can not apply to the whole population.
Brain plasticity
Plasticity = ability to change its structure (physically) and function as a result or reaction to an environment, experiences or new learning.
Synaptogenesis = new synapses are formed, infancy = has an explosion of synaptic formation (exuberant synaptogenesis).
Neurogenesis = new neurons grow, infant = populates the growing brain with neurons.
Synaptic pruning (axon pruning) = synapse elimination, early childhood and onset puberty.
Experience expectant plasticity
Infants have rapid growth in synaptic connections, 15,000 by 2-3 years.
Synaptogenesis = twice as many as adults.
As we get older = less used get deleted (synaptic pruning) + most used get strengthened.
Brain = not blank.
Brain = actively shapes neural connections on expected environments that are inputted during certain developmental windows.
Early experiences shape neural pathways of the developmental brain.
Experience dependent plasticity
Brain = makes new neural connections, adapts to new experiences as a result of learning a way.
Kuhn et al 2014 = saw benefits in playing mario kart for 2 months 30 minutes a day, found - increased connections in the hippocampus (navigational skills), cerebellum (visual-motor learning to play the game), pre-frontal cortex (learning when new behaviours are appropriate/ planning), supported synaptogenesis (more grey matter = increased function).
Brain = not static but changes due to different experiences.
Maguire et al 2000 = studied the brains of London taxi drivers, MRI scans, found - more grey matter in the posterior hippocampus (navigational and space skills), positive correlation between time as a cabbie and more structural difference, had to take ‘the knowledge’ assesses recall of streets and routes.
Brain = adapts and reorganises as a result of new neural connections even in adulthood.
Koppelmans et al 2016 = studied the effects of space and how it affects the brain, 27 astronauts, brain scans before space mission and when returned, 2 weeks to 6 months - cerebellum shrunk (positive correlation between amount of shrinkage and time in space), motor and somatosensory were swollen.
Brain = reorganises due to the change in environment.
Functional recovery
Functional recovery = moving of functions from a damaged area of the brain after a trauma to the an undamaged area.
3 processes = neural regeneration, neuronal unmasking, neural reorganisation.
Follows physical injury or infection (meningitis) or stroke experience.
Experience loss of brain function including paralysis, aphasia (issues with language), memory loss or difficulty in perception.
Unaffected areas can adopt or compensate for the damaged areas.
Function recovery = example of neural plasticity (happens quickly after trauma then eventually slows - spontaneous recovery).
Neural regeneration
Axon sprouting.
Happens = new nerve endings grow and connect with the undamaged areas.
Compensates for damaged areas.
Enables the recovery of lost functions.
Example of synaptogenesis.
Neuronal unmasking
Dormant synapses (exist anatomically but blocked from functioning) open and become functional.
Happens = surrounding brain area is damaged, rate of input to dormant increases opening connections to not normally activated regions.
Gradual development of a new structure.
Example of synaptogenesis/ neurogenesis.
Neuronal reorganisation
The brain transfers functions from a damaged area to an undamaged area.
Example = Broca’s area in the left becomes damaged then areas in the right may take over.
Extreme and intensive therapy = whole areas can take over the functions of damaged areas.
Danelli 2013 = case study of a boy who had most of his left hemisphere removed at the age of 2 ½ to remove a tumour, with intensive therapy the right hemisphere took over the functions of the left hemisphere like language and speech.
Strength of plasticity and functional recovery
Research support:
Danelli 2013 studied an Italian boy EB who removed most of the left hemisphere to remove a tumour, intensive therapy.
The right took over functions normally from the left like language and speech.
EB shows maximal plasticity.
Shows brain is capable of reorganising itself through functional recovery.
Supports plasticity working to help recovery even at young ages.
Weakness of plasticity and functional recovery
Case study has low population validity:
Danelli 2013, EB relates to young Italian male.
Androcentric results are not representative of females or different age groups.
Support for plasticity and functional recovery but only for males not generalisable which causes doubt for the idea.
Strength of plasticity and functional recovery
Practical applications:
Gazzaley et al 2013 studied individuals who suffered cognitive decline like early dementia.
They were prescribed a diet of playing video games on a daily basis.
Brains become organised and efficient.
Neuroracer - preserves cognitive function.
The field of plasticity and functional recovery can help individuals in recovery from cognitive decline.
Due to technology advances from research findings.
Weakness of plasticity and functional recovery
Recovery from brain trauma is not universal:
Age - plasticity decreases with age.
Teubar 1975 found a negative correlation between age and recovery in soldiers.
60% under 20 had huge improvements, 25% over 25 similar improvements.
Females recover from brain trauma more as progesterone acts as a neuroprotective agent, modulates inflammation and antioxidants and brains are less lateralised.
Education - matheas 2015 did a meta analysis which found a positive correlation with high IQ and educational background.
Affected by individual differences.
Not all can benefit from functional plasticity.
Biological rhythms
Any change in physiological activity that repeats periodically in a set (cyclical) pattern.
Infradian cycle
More than 24 hours
Menstrual cycle
Regulated by hormones.
Promote ovulation.
Stimulate uterus fertilisation.
Ovulation halfway.
16 to 32 hours.
Progesterone increases for preparation of embryo implantation
Normally - 28 days (23 or 36).
Support for menstrual cycle
Penton-volk et al 1999.
Women expressed a preference for feminine facial features when they are less fertile and more masculine when they are most fertile.
Heterosexual women’s sexual behaviour is motivated by the cycle.
Important for understanding human behaviour.
Hibernation
Reduced metabolic activity.
Conserve energy.
Survive extreme cold.
Reduced food availability.
Body temperature drops.
Heart rate slows down.
Breathing becomes shallow.
Support for hibernation
Toien et al.
Probability of a bear showing infradian rhythms during hibernation was 79%.
24 hour light/ dark cycle has no effect.
Long term and is seasonal.
Extends more than 24 hours.
Ultradian cycle
Less than 24 hours
Sleep cycle
Stages 1 and 2 are ‘light sleep’ where brain wave patterns become slower starting with alpha then progressing to theta waves.
Stages 3 and 4 are ‘deep sleep’ where it is difficult to wake someone and is associated with delta waves.
Stage 5 is REM or dream sleep where the body is paralysed but brain activity resembles that of an awake person.
The cycle repeats every 90 minutes.
Support for sleep cycle
Dement + kleitman 1957.
Found different brain waves at regular intervals during sleep.
9 male pts for up to 61 nights in a lab.
Found REM and NREM.
Sleep is an active state with many stages and an average complete cycle of 90 minutes.
Woke up pts during REM a dream was reported 79% of the time whilst only 75 in NREM.
Circadian cycle
Approximately 24 hours.
Body temperature
Lowest in the morning - 36c at 4:30 am.
Highest in early evening - 38c at 6pm.
Sleep happens when core temperatures drop.
Body temperature rises towards the end of sleep.
Influenced by muscular activity, digestion, heat loss and heat production.
Support for body temperature
Buhr et al 2010.
Fluctuations in temperature set the timing of cells in the body and cause tissues and organs to become active or inactive.
Light levels transform to neural messages which set body temperature.
Sleep/ wake cycle
Determines our pattern of wakefulness and sleepiness.
Dips and rises at certain times.
Strong sleep drive = occurs in two dips, 2-4am and 1-3pm.
Sleepiness dips is less intense if we have had enough sleep and more intense when we are tired.
Influenced by endogenous and exogenous pacemakers
Endogenous pacemakers
Internal mechanisms that influence the patterns of our biological rhythms.
Pacemaker = controls physiological rhythmic activity.
Could be genetic mechanisms which help maintain regular rhythms when zeitgebers are not present.
Not perfect and need zeitgebers to synchronise rhythms to our individual behaviour.
Zeitgebers = an external or environmental cue that synchronises a biological rhythm e.g. light and dark.
Examples: pineal gland and suprachiasmatic nucleus/ SCN (internal clock).
The role of endogenous pacemakers in the sleep/wake cycle
SCN is found in the hypothalamus which synchronises our sleep/ wake circadian rhythm.
SCN receives light through the optic nerve.
Light levels drop = information is received by SCN which fires impulses to the pineal gland which secretes more melatonin resulting in sleepiness.
Melatonin = acts as a help to decrease brain activity.
Light increases = melatonin levels fall making us more awake and increases brain activity.
No light as a zeitgeber = process ‘runs free’ to an average 25 hour cycle.
How are other neurotransmitters linked to the sleep/ wake cycle?
Serotonin + dopamine = determines quality of sleep (how well and how long), serotonin makes melatonin.
Noradrenaline = high levels need to be maintained by good sleep habits, causing sleep loss (especially REM).
Strength of endogenous pacemakers
Role of exogenous zeitgebers (EZ) has case study evidence to support endogenous pacemakers (EP):
Siffre (French explorer) spent 6 months in an underground cave in 1972 in Texas.
When body could ‘free run’ away, his body settled on a 25-30 hour regular pattern.
The internal body clock regulated sleep/ wake cycles with no natural light.
EP’s are important in regulating circadian rhythms but EZ also plays a role.
Weakness of endogenous pacemakers
Studies used for EP’s are case studies:
Siffre’s case study was on his body settling to the 25-30 hour cycle in an underground cave.
One off study.
May not represent other experiences as how he adjusted and what he did with his time may be different.
Provides results that can not be generalised.
Limits full understanding of EP controlling circadian rhythms.
Strength of endogenous pacemakers
Scientific evidence from lab experiments that support EP role in regulating circadian cycles:
Ralph et al took out SCN from a mutant hamster with a circadian rhythm of 20 hours.
Transplanted SCN to normal adult hamsters' brains.
Normal hamsters took on the circadian rhythm of mutant hamsters.
DeCoursey et al destroyed the SCN of 30 chipmunks which destroyed their sleep/ wake cycle.
Suggests circadian rhythms are objective physiological processes.
Can be studied in a controlled environment to show the cause and effect of SCN in sleep/ wake cycle.
Weakness of endogenous pacemakers
Use of animal studies may be an issue when looking at the role of EP’s in circadian rhythms:
Results may be difficult to extrapolate in order to explain human brains.
Some animals are nocturnal so will have a different sleep/ wake cycle compared to humans.
Humans are more adaptable when adjusting to circadian rhythms.
Limited biological continuity.
Animal studies have limited value.
Results can not be generalised to understand impacts of EP’s on human biological rhythms.
Exogenous zeitgebers
Outside the organism.
External stimuli/ environmental cues that are responsible for resetting the biological clock.
Provides information about elapsed time and prompt changes in bodily activity.
EZ triggers biological rhythms.
Example = light (most important to rest the body clock each day, key zeitgeber, reset the main endogenous pacemaker which is the SCN, impacts melatonin production and sleep/ wakefulness, indirect influence on hormone circulation and blood circulation, main focus is sleep), temperature, noise, clocks.
Role of exogenous zeitgebers
1972 = Siffre went into Midnight Cave in Texas.
He stayed there for 6 months with a tent, bed, table, and chair.
Had a supply of frozen food and 780 gallons of water.
When he woke up and thought it was daytime = phoned the research team above ground who would switch the lights on in the cave.
Daily experiments = blood pressure, memory and physical tests.
Felt tired = thought it was nighttime, the research team above would turn the lights off and he would go to sleep.
First 35 days = sleep/ wake cycle of 26 hours.
Day 37 = stayed up for a few more hours and then slept long.
Day 63 = returned to a 26 hour cycle.
Nine weeks later = cycle became more varied and random for 20 days.
Sometimes it was 48 hours like people in previous studies.
Varied = 18-52 hours.
Day 150 = returned to a 26 hour cycle.
Conclusion = time is not something that humans could work with and understand without any external environmental cue.
Strength of exogenous zeitgebers
Research evidence to support EP and EX in regulating circadian rhythms:
Vetter et al studied the effects on workers' sleep/ wake patterns by changing the light at the workplace.
Changed from 4000 kelvin (k) which is artificial ‘natural’ warm light to 8000 k which is a blue enriched office light which is similar to natural daylight.
Artificial blue-enriched light competes with artificial warm light as a zeitgeber.
Pts with 4000k warm light synchronised to natural dawn.
Pts with 8000k blue enriched light synchronised to office hours.
Blue light = stronger and set schedules.
Supports the idea that daylight is the dominant EZ in the human sleep/ wake cycle.
Weakness of exogenous zeitgebers
Many studies used to support are done in lab environments with artificial tasks:
Vetter used artificial blue light at 8000k and artificial warm light 4000k for 2 groups of workers.
This was to see if their sleep/ wake cycle was adjusted.
Used an artificial task which could affect the way that body clock would naturally work.
Has low ecological validity.
May not provide credible evidence.
Weakness of exogenous zeitgebers
Individual differences need to be included as some roles may be underestimated:
Some people are more alert early in the day and others later in the day.
Due to their lifestyles or ages.
The speed we adapt to disruptions can vary so it is difficult to see if the person's lifestyle is the cause and effect of their circadian cycles.
The role of EP and EZ’s is not causal or universal.
Due to variables like age, lifestyle, personality, culture.
Disrupted biological rhythms can have negative consequences
Imbalance of EP + EZ = disrupts the sleep wake cycle.
Natural environment = zeitgebers normally change slowly like light levels during the year.
Modern society = zeitgebers can change quickly like shift work and jet lag.
Negative effects on our ability to function.
Slows reaction times, impairing problem solving skills and limiting concentration.
Jet lag
When the body’s internal body clock is being out of step with external cues.
Results in fatigue, insomnia, anxiety, constipation, dehydration.
Bodies make two adjustments when crossing time zones.
Phase advance = getting up or going to bed earlier than usual.
Phase delay = getting up or going to bed later than usual.
Easier to adjust to phase delay as it is lengthening our day and we have seen our internal rhythm extend further than 24 hours.
Shift lag
Other species = governed by natural laws and in built biological rhythms.
Only humans suffer working outside of their biological rhythms.
20% of workers work some form of rotating or permanent unsocial shift pattern.
Psychological effects = mood disorders like depression and anxiety, cognitive issues like bad memory and attention, burn out.
Physical effects = fatigue, sleep disorder like insomnia, digestive problems, increased risk of type 2 diabetes, cardiovascular disease.
Czeisler = researcher says a slow rotation of 3 weeks on each shift.
Bambra = prefers a faster rotation of just 3-4 days on each pattern so the body does not have time to adjust to the new cycle.
The rotation can be clockwise or anticlockwise.