biopsychology

what are the 2 major psychological systems that regulate behaviour in response to the environment in the body?

nervous system and endocrine system

what is the nervous system?

a network of cells in our body. it is the primary internal communication system

functions of the nervous system

to collect, process and respond to info in the environment
to coordinate the working of different organs & cells in the body

what is the nervous system made up of?

central nervous system and peripheral nervous system

what is the peripheral nervous system made up of?

somatic and autonomic nervous systems
the autonomic nervous system is split into the sympathetic and parasympathetic branches

what is the central nervous system?

The CNS is made up of the brain & the spinal cord.

the CNS passes messages to & from the brain & connects nerves to the PNS; it's the origin of all complex commands and decisions.

brain

the brain is the centre of all conscious awareness. the brain's outer layer, the cerebral cortex, is highly developed in humans and is what distinguishes our higher mental functions from those of animals. only a few living creatures don't have a brain. the brain is divided into 2 hemispheres.

spinal cord

the spinal cord is an extension of the brain. it is responsible for reflex actions such as pulling your hand away from a hot plate.

what is the peripheral nervous system?

the PNS transmits messages, via millions of neurons (nerve cells) to and from the CNS. the PNS is further sub-divided into the autonomic & somatic NS.

the PNS sends info to the CNS from the outside world, and transmits messages from the CNS to muscles & glands in the body.

made up of somatic and autonomic nervous systems

autonomic nervous system is split into the sympathetic and parasympathetic branches

transmits info to & from internal bodily organs. it is 'autonomic' as the system operates involuntarily (automatic). it has 2 main divisions - the sympathetic & parasympathetic NS. the ANS governs vital functions in the body such as breathing, heart rate, digestion, sexual arousal & stress responses.

somatic nervous system (SNS)

transmits info from receptor cells in the sense organs to the CNS. it also receives info from the CNS that directs muscles to act. the SNS controls muscle movement & receives info from sensory receptors.

what is the endocrine system?

controls vital functions in the body. acts much more slowly than the NS but has very widespread & powerful effects. it's made up of a series of glands throughout your body which release chemicals known as hormones.
hormones are secreted into the bloodstream & affect any cell in the body that has a receptor for that particular hormone

pituitary gland

the 'master gland'. controls the release of hormones from all the other endocrine glands in the body.

produces thyroxine. affects cells in the heart to increase heart rate. also affects cells throughout the body increasing metabolic rates. this in turn affects growth rates.

adrenal gland

a pair of endocrine glands that sit just above the kidneys and secrete adrenaline. regulates fight or flight response.

pancreas

produces insulin & glucagon - involved in regulating blood glucose levels

ovaries

produces oestrogen. involved in the development of female sex organs

testes

produces testosterone. involved in puberty/development in males.

fight or flight response

this response is due to the ES and autonomic NS working together. it's a reflex response - designed to help the individual cope physically under any threat - activated under times of stress. it helps the individual to react quicker than normal

process of the fight or flight response

1) when an environmental stressor is perceived (e.g. your friend jumps out to frighten you) the first thing that happens is the hypothalamus activates.
2) this triggers activity in the sympathetic branch of the autonomic NS (the ANS changes from resting state, parasympathetic branch, to sympathetic state).
3) at the same time, the adrenal gland releases adrenaline into the bloodstream.
4) this causes a series of changes in our body allowing us to fight/flight.
5) finally, once the threat/stressor has passed, your body returns to the parasympathetic NS and the physiological changes revert - its actions are antagonistic to the sympathetic system.

what body changes occur when the sympathetic branch is activated?

what body changes occur when the sympathetic branch is activated?

neurons

nerve cells - there are 100 bill neurons in the human NS, 80% of which are located in the brain.
by transmitting signals electrically and chemically, these neurons provide the NS with its primary means of communication
they vary in size from less than a mm to over a m long
they transmit info from 1-268 mph

sensory neurons

neurons that carry messages from the PNS to the CNS
they have long dendrites and short axons
convert external stimuli from the organisms environment into internal electrical impulses

relay neurons

these connect the sensory neurons to the motor or other relay neurons
they have short dendrites and short axons.

motor neurons

neurons that carry signals from the CNS to the effectors such as muscles and glands
they have short dendrites and long axons

structure of a neuron

cell body, nucleus, dendrites, axon, myelin sheath, node of ranvier, axon terminal

cell body

contains the nucleus

nucleus

contains the genetic material of the cell

dendrites

branding extensions which carry nerve impulses from neighbouring neurons towards the cell body

axon

carries electrical impulses away from the neurons cell body towards the axon terminal

myelin sheath

protects/insulates the axon. speeds up electrical transmission of the impulse

node of ranvier

a gap between successive segments of the myelin sheath. these gaps speed up the transmission of the impulse by forcing it to 'jump' across the gaps along the axon

axon terminal

end of axon. communicate with the next neuron in the chain across a gap known as the synapse

process of synaptic transmission

electrical impulse will travel down pre-synaptic neuron reaching axon terminals. this will activate vesicles stored here which all contain neurotransmitters. neurotransmitters are chemicals which allow 2 neurons to communicate.
now, the message is chemical. the NT diffuse across the synapse and bind to the receptor sites in the post-synaptic neuron (dendrites) - certain NT's will only bind to certain receptor sites, like a lock and key.
when the NT's bind, they will either be excitatory or inhibitory. if they are excitatory the post-synaptic neuron is more likely to fire the electrical charge. inhibitory - less likely to fire.
summation - as both E & I NT fire, what happens for the next neuron is which ever NT is in majority.

what is the synapse/synaptic cleft?

the small gap between two adjacent neurons

the small gap between two adjacent neurons

holistic idea = all parts of the brain are involved in the processing of thought & action - whenever we do a behaviour it requires our whole brain.
localisation of function = each part of the brain has its own unique function - they perform different tasks and are involved with diff parts of the body i.e. skills, behaviour etc. are all localised. if a certain part of the brain becomes damaged through illness or injury, the function associated with that area will also be affected/lost.

structure of the brain

both hemispheres contain: frontal lobe, motor cortex, somasensatory cortex, parietal lobe, temporal lobe, occipital lobe
only the left hemisphere contains Broca's area and Wernicke's area

left and right hemispheres of the brain

brain is divided into two halves. connected by a bundle of nerves called the corpus callosum.
your left hemisphere controls the right side of your body.
your right hemisphere controls the left side of your body.
the cerebral cortex is the outer layer of both hemispheres - about 3mm thick. separates us from animals because the human cortex is much more developed. often called 'grey matter' due to the look of all the cells.
each hemisphere is divided up into 4 lobes - frontal, parietal, temporal, occipital

frontal lobe

contains the motor area which controls voluntary movement in the opposite side of the body. damage to this area of the brain may result in a loss of control over fine movements (voluntary movements in app side of body)

parietal lobe

contains the somasensatory area. separated from the motor cortex by a 'valley' called the central sulcus. this area is where sensory info from the skin (e.g. heat, touch, pressure etc.) is perceived. receptors for our face & hands occupy over half the area

occipital lobe

the visual area - where all your sight is processed. the left eye goes to the right occipital lobe and the right eye goes to the left occipital lobe. damage to the occipital lobe can result in blindness.

temporal lobe

auditory area - analyses speech-based (auditory) info. damage can lead to loss of hearing. damage to a specific area, Wernicke's area, may affect the ability to comprehend language.

which side of the brain controls language?

left side

broca's area

left frontal lobe, speech production
if damaged you will suffer from Broca's aphasia - slow, laborious speech which lacks fluency.
their intelligence & speech comprehension remain intact - they understand q's and answers will be relevant, just can't speak fluently

wernicke's area

left temporal lobe, language comprehension (understanding speech)
damage causes Wernicke's aphasia - problems in understanding speech. they produce random/meaningless words.
have no problem in producing language.

strengths of localisation of function

+ brain scan studies support the idea of localisation
Peterson (1988) used brain scans (MRI) to measure what the brain was doing while ppts did tasks - diff areas were active for diff tasks.
Broca's area was active for a reading task and Wernicke's area was active in a listening task.
this supports localisation because it shows that our brains functions are localised to 1 area - not holistic

+ case studies support localisation
Phineas Gage - damaged frontal lobe in accident. affected his personality. before he was calm and rational, after he was quick tempered and irrational.
supports localisation as it shows the frontal lobe is responsible for mood regulation

- Lashley's research contradicts localisation
he removed areas of the cortex (10-50%) in rats that were learning a maze. no area was proven to be more important than any other area in terms of the rats' ability to learn the maze. what affected the rats' learning was how much was removed.
this weakens localisation as it implies a higher cognitive skill such as learning may be holistic (requires every part of the cortex)

- Plasticity weakens localisation
the brain is 'plastic' - it can change/repair itself. when the brain has become damaged and a particular function has been comprimised or lost, the rest of the brain appears able to reorganise itself in an attempt to recover the lost function.
weakens localisation - suggests any part of the brain can do any function

what is the old view of the brain?

that it does not change - it is a fixed object from birth

what is the new view of the brain?

our brain is 'plastic' - it can change, grow and repair

plasticity

the brain's ability to change and adapt (functionally and physically) as a result of experience & new learning

what happens to the brain during infancy?

the brain experiences a rapid growth in neurons and new synaptic connections
at age 2-3 years we have around 15,000 synaptic connections
there are twice as many connections than there are in the adult brain

what happens to the brain as we age?

rarely used connections die, skills we frequently use grow new connections
synaptic pruning - things we no longer use are deleted, things we frequently use are developed/ strengthened
as we get older our brain becomes less plastic
it is much harder to learn a new skill - this also applies to recovery

research on plasticity

Maguire and draganski's research both show how our brain is plastic and can change through experience

Maguire's research on plasticity (2000)

she studied the brains of London taxi drivers
taxi drivers had to pass a 'knowledge test' - which was on their spatial knowledge of London
found that taxi drivers had more grey matter in their posterior hippocampus compared to a control group
so, the practice of taxi driving had changed the part of their brain responsible for navigation & spatial skills
found a positive correlation between time as a taxi driver and amount of grey matter in hippocampus - more time as taxi driver = more grey matter

Draganski's research on plasticity (2006)

studied the brains of medical students before and after their final exams
they found after the exam the students had far more grey matter in parts of the parietal lobe

functional recovery of the brain after trauma

following brain damage (e.g. from a stroke) your brain will sense the damage & unaffected areas will try and help the damaged areas regain functions
this process occurs very quickly after trauma but will slow down over time & often will not fully repair the brain - spontaneous recovery
after this, the individual will need neurorehabilitation to fully repair their brain

what happens in the brain during recovery?

the brain can re-wire and reorganise itself by forming new synaptic connections close to the area damage.
secondary neural pathways that wouldn't typically be used to execute functions are activated to enable continued function, often in the same way as before.

3 structural changes in the brain during recovery

axonal sprouting: growth of new nerve endings to connect to undamaged parts which had lost connections - forming new neuronal pathways
reformation of blood vessels
recruitment of homologous areas: this is where similar areas on the opposite side of the brain will try to help carry out the function of the part of the brain lost

strengths of plasticity

+ contributed to neurorehabilitation
due to the increase in knowledge on plasticity, we have been able to create therapies to help people with brain damage
techniques such as movement therapy and electrical stimulation are used - encourage the brain to regrow connections that have been lost
this strengthens the study of plasticity as the knowledge we have gained has allowed us to improve & help many people lives

+ supporting evidence for brain plasticity
Hubel & Wiesel (1963) - sewed the eye of a kitten shut and analysed the brains cortical response
they expected, if localisation is true, that the occipital lobe that processes the shut eye would be inactive (no stimulus)
they found, however, it was active - it was helping the other occipital lobe process the 1 open eye
this supports plasticity showing that the brain can re-wire itself following trauma

weaknesses of plasticity

- plasticity may result in maladaptive changes
Medina (2007) found that persistent use of drugs led to a dramatic loss in cognitive functioning. it also increases the risk of dementia later in life and strokes
Hirstein (2008) found that up to 80% of amputees had experiences of phantom limb syndrome. for nearly all this was a pain sensation
this shows that whilst plasticity can be good and help people, the fact our brain can change can also lead to negative consequences

- plasticity reduces with age
functional plasticity reduces with age. this means that it will be a lot harder for an older individual to repair their brain following trauma
However, a study found that it can still change later in life:
a study got elderly individuals to play 40 hours of golf, taking brain scans before & after. found that their brain had developed more grey matter in motor cortex
so, whilst more difficult it is not impossible for the brain to change

ways of investigating the brain

fMRI
EEG
ERPs
Post Mortem

functional magnetic resonance imaging (fMRI)

a method used to measure brain activity while a person is performing a task that uses MRI technology (detecting radio waves from changing magnetic fields).
this enables the researcher to detect which regions of the brain are rich in oxygen and thus are active.

when a brain area is more active it consumes more oxygen to meet this increased demand. produces 3D images (activation maps) showing which parts of brain are involved in a particular mental process.

strengths of fMRI scans

+ doesn't rely on radiation
+ virtually risk-free, non-invasive, straightforward to use
+ produces images with very high spatial resolution, depicting detail by the mm, and providing a clear picture of how brain activity is localised

weaknesses of fMRI scans

- expensive
- can only capture a clear image if person stays perfectly still
- poor temporal resolution as there's a 5-second time-lag behind the image on screen & the initial firing of neuronal activity
- can only measure blood flow in the brain, it can't home in on the activity of individual neurons so it's difficult to tell exactly what kind of brain activity is being represented on screen

electroencephalogram (EEG)

EEG

strengths of EEGs

+ invaluable in the diagnosis of conditions such as epilepsy
+ contributed to our understanding of stages involved in sleep
+ extremely high temporal resolution - can accurately detect brain activity at a resolution of a single millisecond

weaknesses of EEGs

- generalised nature of info received
- poor spatial resolution: not useful for pinpointing the exact source of neural activity
- doesn't allow researchers to distinguish between activities originating in different but adjacent locations

event-related potential (ERP)

using a statistical averaging technique, all extraneous brain activity from the original EEG recording is filtered out leaving only those responses that relate to, say, the presentation of a specific stimulus or performance to a specific task. what remains are event-related potentials: types of brainwave that are triggered by particular events. these are linked to cognitive processes such as attention & perception

strengths of ERPs

+ bring much more specificity to the measurement of neural processes than could ever be achieved using raw EEG data
+ excellent temporal resolution - this has led to their widespread use in the measurement of cognitive functions & deficits
+ researchers have been able to identify many diff types of ERP and describe the precise role of these in cognitive functioning

weaknesses of ERPs

- lack of standardisation in ERP methodology between diff research studies which makes it difficult to confirm findings
- in order to establish pure data in ERP studies, background noise and extraneous material must be completely eliminated - not always easy to achieve

post-mortem examinations

The brain is analysed after death to determine whether certain observed behaviours during the patient's lifetime can be linked to abnormalities in the brain.

individuals whose brains are subject to these are likely to be those who have a rare disorder and have experienced unusual deficits in mental processes or behaviour during their lifetime. areas of damage are examined after death as a means of establishing the likely cause of the affliction the person suffered.
may involve comparison with a neurotypical brain in order to ascertain the extent of the difference

strengths of post-mortems

+ vital in providing a foundation for early understanding of key processes in the brain
+ Broca & Wernicke relied on post-mortem studies to establish links between language, brain & behaviour decades before neurimaging ever became a possibility
+ improve medical knowledge and help generate hypotheses for further study

weaknesses of post-mortems

- causation: observed damage to the brain may not be linked to the deficits under review but to some other unrelated trauma or decay.
- raise ethical issues of consent from patient before death; may not be able to provide informed consent due to their condition

hemisphere lateralisation

the idea that each hemisphere of the brain is functionally different - has its own function.
certain neural processes & behaviours are mainly controlled by the left and others are done by the right. e.g. language in the left
we study this by looking at split-brain patients

split-brain studies

Sperry's (1968) studies involved a unique group of individuals (split-brain patients), all of whom had undone the same surgical procedure - a commissurotomy.
they had the corpus callosum cut, meaning their 2 hemispheres could not communicate. (the corpus callosum is a bundle of nerves that allow the 2 hemispheres to communicate
they had this cut to try and cope with their epileptic seizures.
this meant the main communication line between the 2 hemispheres was removed. this allowed Sperry to test & see what each hemisphere's function was, and whether the hemispheres performed tasks independently of one another

split-brain procedure

Sperry devised a general procedure where ppts would stare at a fixation point in the middle fo a screen.
a diff word or image would be flashed either side of the point. this would be really fast (1/10th of a second) to ensure only 1 eye saw the stimulus (so only 1 hemisphere processes it)
the word/image projected to the right visual field is processed by the left hemisphere, and the left visual field is processed by the right hemisphere.
would then ask them a series of questions to see what that hemisphere can do.

key findings of split-brain research

describing what you see: when a picture was shown to right visual field, the patient could easily describe what was seen. if it was shown to the left visual field, the patient could not describe what was seen - typically recorded there was nothing there. language is processed in left hemisphere - patients inability to describe objects in LVF was due to lack of language centres in RH

drawing task: whilst patients can't name image in LVF, if asked to draw what they saw with left hand they can correctly draw the appropriate object. indicates the RH does know what it saw, just lacks the lang ability to say it - it controls drawing

matching faces: RH is dominant in facial recognition. when asked to match a face from a series of other faces, picture processed by RH was constantly selected, whilst picture presented to the LH was consistently ignored.

what did Sperry conclude from his split-brain research?

the left hemisphere is crucial for language and the right hemisphere is dominant in drawing and facial recognition

strengths of split-brain research

+ Sperry's work advanced our understanding of the brain
his work led to the knowledge that our LH is responsible for analytical and verbal tasks whilst the RH is responsible for spatial tasks & facial recognition
this knowledge has been useful in many future studies & therapies and we credit Sperry for being the first person to create this idea

+ highly controlled procedure
Sperry created his unique method which allowed him to test the 2 hemispheres. his idea of having a fixation point & flashing the image very quickly (1/10th of sec) meant he could test them by only presenting the visual info to 1 hemispheric field at a time.
it was in a highly controlled lab environment with standardised procedures which have allowed many people to replicate it in the future.
strength because it's scientific, objective & has high validity

weaknesses of split-brain research

- difficult to generalise his findings
split-brain patients were an unusual sample: only tested 11 people, all of whom had a history of epileptic seizures.
however, his control group of 11 people were individuals who had a split-brain but no history of epilepsy - this is a problem because we don't know if Sperry's patients performance was due to the history of epilepsy or split-brain (he has 2 IV's)
this weakens his study as we cannot draw any firm conclusions about hemisphere lateralisation from his study

- Sperry overemphasised the differences between hemispheres
modern neuroscientists argue that there is not such a distinct difference between the 2 hemispheres and that they can do most tasks when required (plasticity)
in the normal brain the 2 hemispheres are in constant communication when performing everyday tasks, and many of the behaviours typically associated with 1 hemisphere can be effectively performed by the other when the situation requires it.
this weakens Sperry as it suggests he may have exaggerated his findings.

what is a biological rhythm?

a change in an individuals bodily activity that conforms to a cyclical pattern

what governs biological rhythms?

endogenous pacemakers - internal body clock
exogenous Zeitgebers - environmental factors

what are the 3 biological rhythms?

circadian rhythm - lasts for 24 hours (sleep/wake cycle)
infradian rhythm - 24 hours + (menstruation & SAD)
ultradian rhythm - less than 24 hours (sleep stages)

what is a circadian rhythm?

any bodily process that you experience in a cyclical pattern every 24 hours
e.g. sleep/wake cycle & core body temp

endogenous pacemakers in sleep/wake cycle

EPs are the internal body clocks that are thought to regulate circadian rhythms.
suprachiasmatic nucleus (SCN) is thought to be the primary pacemaker
SCN - a bundle of nerves located in the hypothalamus. primary EP. it is located just above the optic chiasm, which receives info from eyes about light (happens even when eyes are closed)

AO3 for SCN (EP)

+ supporting evidence
Decoursey (2000) removed SCN from 30 chipmunks' brains. they then put them back into the wild. found that most of them were eaten by predators. this was because they had lost their typical sleep/wake pattern meaning they were awake when they should have been asleep. this supports SCN as primary pacemaker because without it they had no sleep/wake cycle.

- generalisation issues
study done on chipmunks, not humans therefore we can't be sure if SCN plays the same role in humans

- ethics
is harming/killing animals worth the knowledge gained?

exogenous zeitgebers in sleep/wake cycle

any environmental factors that influence our biological rhythms. e.g. light and social cues

light - plays a role in maintenance of sleep/wake cycle, it can re-set the SCN. it has many indirect effects on our body - it can increase production of hormones etc.

social cues - schedules imposed by parents can have an effect on the child's sleep/wake cycle i.e. meal time and bed times. setting times for these things entrains our sleep/wake cycle around it. adapting to local eat and sleep times is effective at entraining CR and beating jet lag

AO3 for light

+ supporting evidence
Campbell & Murphy (1998). got ppts to sleep in a dark room. shone a bright light to the back of their knees (wanted to see if light receptors are not just in eyes). they found that this light was enough to change their sleep/wake cycle by up to 3 hours. this supports light as a powerful EZ as it can change the SCN

AO3 for EZ

+ light (on prev card)

- issues with influence of EZ
Holens case study of a blind man, who, from birth, had a sleep/wake cycle of 25-26 hours. no amount of environmental influence could ever change this rhythm. this suggests that EZs may not be as powerful in sleep/wake cycles as first thought (but this is just 1 person)
also people in arctic regions experience 24 hours day light in summer but still have normal sleep/wake patterns.

Siffre's case study (aim)

Siffre wanted to know what was more influential on sleep/wake cycle - the EP or EZ
Siffre decided to test the EP without influence of EZ - he called this the 'free-running' clock

Siffre's case study (procedure)

Siffre was a self-styled caveman who spent several extended periods underground to study the effects on his own biological rhythms.
deprived of exposure to natural light and sound but had access to adequate food and drink

Siffre's case study (findings)

he resurfaced in mid-september 1962 after 2 months in the caves of the southern alps believing it to be mid-august.
a decade later he performed a similar feat but this time for 6 months in a texan cave.
his 'free-running' biological rhythm settled down to one that was just beyond the usual 24 hours (~25 hours) though he did continue to fall asleep and wake up on a regular schedule

strengths of circadian rhythms

+ practical applications in drug treatments
knowledge of CR has helped us to design drugs to be more effective. knowledge of various bodily processes (heart rate, digestion) has taught us when will be best to give a drug for optimum effect. at certain times of the day our bodily processes will be better for distributing a drug around out body. this has led to guidelines to do with the timing of drug dosing for a whole range of medications e.g. anticancer dugs. this has all come about due to increased knowledge of CR

+ practical applications in shift work
knowledge on CR & sleep/wake cycle has given us a better understanding of the negative consequences of shift work. Knutson found that shift workers are 3x more likely to suffer from heart disease and increased risk of strokes and dementia. this knowledge has led to better understanding of consequences and a change in policy.

weaknesses of circadian rhythms

- generalisation issues
studies of sleep/wake cycle involved a small group of ppts, or single individuals like Siffre. people involved may not be representative of winder pop - this limits the extent to which meaningful generalisations can be made. Siffre: case study of 1 man, can't say with confidence that his findings would be the same in everyone else. he can't even generalise himself as he retested himself years later & found a different finding. this weakens his study dramatically. (illustrates that, even when same person is involved, there are factors that vary which may prevent general conclusions being drawn)

- validity of findings questionable due to poor control
Siffre believed he was testing a free-running clock due to no natural light. however, he took a lamp in with him, and we now know that artificial light can have just the same effect as natural light. this means Siffre didn't test what he intended & we know little about the free-running clock.

what is an infradian rhythm?

a biological rhythm that has a cycle of longer than 24 hours e.g. menstruation & SAD

menstrual cycle

governed by monthly changes in hormone levels.
day 1: womb lining is shed; end of cycle is day before next period.
typical cycle is approximately 28 days.
during the cycle, oestrogen increases, causing the ovary to develop an egg and release it - ovulation.
after ovulation, progesterone helps womb lining thicken preparing the body for pregnancy.
if pregnancy does not occur, the egg is absorbed into the body, the womb lining leaves the body (the menstrual flow)

research study on menstrual cycle

although MS is an endogenous system, evidence suggests that it may be influenced by exogenous factors (cycles of other women).
McClintiock (1998) collected samples of pheromones from women with regular periods at diff stages of their MS, via a cotton pad on armpit. the pads were rubbed on the upper lip of other ppts (irregular periods). McClintock found that 68% of women experienced changes to their cycle which brought them closer to the cycle of their 'odour donor'

AO3 for menstrual cycle

+ support for EZ influence on menstrual cycle
McClintock's study showed that EZ's can have an influence on biological rhythms that seem to be mainly due to EP's

- methodological issues
there are many factors that may affect the menstrual cycle such as diet, exercise, stress etc. that might act as confounding variables in this study as they weren't controlled.
we don't know if synchronisation occurred due to the pheromones or other factors, limiting the validity of the research.
any supposed pattern of synchronisation, as seen in the studies by McClintock and others, is no more than would have been expected to occur by chance

SAD (seasonal affective disorder)

a depressive disorder with a seasonal pattern of prevalence. now diagnosable as a mental disorder in DSM-5.
symptoms = low mood, feelings of hopelessness, lack of interest in life.
has a circannual rhythm - happens on a yearly cycle
'winter blues' - symptoms triggered in winter months when the number of daylight hours becomes shorter
linked to the hormone melatonin
at night, the pineal gland secretes melatonin until dawn when there is an increase in light. during winter, the lack of light in the morning means this secretion process continues for longer.
melatonin has a knock on effect on production of serotonin.

AO3 of SAD

+ practical applications of SAD
research into SAD has led to an effective therapy to help.
phototherapy - Lightbox stimulates natural sunlight in the morning and evening (thought to reset melatonin levels)
studies have found these can relieve symptoms in up to 60% of sufferers.
this supports research in SAD and this infradian rhythm.