Biological Explanations Flashcards
What does key term polygenic mean
Not caused by one single gene, but several genes interacting together
What does key term aetiologically heterogenous mean
The origin of the disorder has different causes
What does the key term candidate gene mean
Any gene thought likely to cause a disease or disorder
Ripke et al study meta analysis
Carried out a meta analysis combining all data from genome wide studies, comparing genetic makeup of. 37,000 patients with 113,000 controls. 108 separate genetic variations were associated with increased risk of schizophrenia. Genes associated with increased risk were genes which coded for the function of neurotransmitters including dopamine
This therefore suggest schizophrenia is polygenic as several genes (108) were interacting with each other associated to SZ
Gottesman et al family and twin study
Gathered secondary data from Danish Civil Register & Danish Psychiatric CentralRegister for over 3.4million people, between 1970 & 2007.
Twin study: found 48% concordance rate for Sz in MZ & 17% for DZ.
Family Study: 13% concordance with their own children; to 2% concordance with Aunts/uncles.
Therefore, the more genetically similar the higher the concordance rate of both family members having Sz. This suggests that Sz is genetic.
EVALUATION - how effective is the GENETIC theory at explaining the cause of schizophrenia
STRENGTH - research support from a family/twin study - Gottesman found a 48% concordance rate for MZ twins and a 17% rate for DZ twins and a 13% comcordance with someone with Sz child compared to 2% with their aunts and uncles - the more genetically similar the more likely to have SZ therefore suggesting it is genetic - However twins share the same environment and they may see their parents as role models (SLT) hence is it biological or due to imitation of behaviour
STRENGTH - research support from an adoption study - 30 SZ mothers had children removed at birth and were adopted compared to 33 non SZ mothers whose children were adopted. SZ mothers - 16.67% concordance rate with their adoptive child. Non SZ mothers = 0% concordance - therefore no shared environment and higher correlation with biological mother suggests that SZ is genetic. However - the trauma of the adoption could account for environmental factors and also 16.67% is still a relatively low concordance.
CRITICISM - it is more likely that it is an interaction of the environment and genetics - if it is 48% concordance for the MZ twins then surely that means SZ is 52% environmental- the distress stress model suggests there is a genetic predisposition to developing SZ but stress and trauma from the environment will trigger someone to develop SZ - however looking at a modern DSM the environment could cause a fault in the genes (epigenetics) therefore not possible to separate the environment and genetics for the cause of SZ
What is the dopamine hypothesis?
Suggests that schizophrenia is caused by abnormal dopamine activity in the brain.
HYPOdopaminergia - lower levels of dopamine and less D2 receptors in the mesocortical (PFC) area of the brain causes an inhibitory firing rate on the post synapse and is thought to link to negative symptoms of SZ
HYPERdopaminergia - higher levels of dopamine and more D2 receptors in the mesolimbic (amygdala and hippocampus) area of the brain causes an excitatory firing rate on the post synapse and is thought to be linked to positive symptoms of SZ
EVALUATION of the dopamine hypothesis explanation of schizophrenia
STRENGTH - research support that HYPERdopaminergia causes positive symptoms of SZ - Amphetamines is a dopamine agonist (floods neuron with dopamine) and when taken by healthy individuals it causes psychotic like symptoms eg hallucinations (positive symptom) - therefore the increase of dopamine must explain positive symptoms of SZ - however it is too reductionist
PEELEEL EV - Ripke found that genes associated with SZ were not only producing dopamine for SZ but other neurotransmitters as well so it is not solely dopamine eg high levels of serotonin, lower glutamate - if other neurotransmitters are involved then the DH is invalid as it doesn’t take only account alternative causes - furthermore negative implications on treatment as of DH is believed then treatment will solely focus on dopamine rather than focusing on other neurotransmitters- however there is evidence of successful treatment as antipsychotics block D2 receptors and have been effective in reducing positive symptoms so dopamine must have a role in SZ
Neural correlates explanation - pre frontal cortex
Function - helps people think logically and organise thoughts
Role in schizophrenics - many schizophrenics have lower activity in this area which could be linked to delusions and disorganised thoughts
Neural Correlates explanation - Visual and auditory cortex
Function - Process information received from the eyes and ears
Role in schizophrenia - schizophrenics have the same activity in these areas when they hallucinate as sane people do when they have genuine auditory and visual experiences
Neural correlates explanation - Basal ganglia
Function - located deep inside the brain and affects movement and thinking skills
Role in schizophrenia- research has shown that this structure is larger in schizophrenics which could cause motor dysfunction
Neural correlates explanation - amygdala
Function - responsible for basic feelings like fear, lust and anger
Role in schizophrenia- smaller in schizophrenics so can link to loss of emotion (affective flattening)
Neural correlates explanation - dopamine
Function - responsible for feelings of pleasure and also affects thinking and movement
Role in schizophrenia- lowe levels are linked to negative symptoms and high levels are linked to positive symptoms
Brain areas in the mesolimbic pathway that link to schizophrenia
Amygdala - fear response - delusions
Hippocampus - memory - overactive - hallucinations
Anterior Cingulate Gyrus - responsible for emotional processing and vocalising speech - auditory/visual hallucinations
Temporal Gyrus - auditory cortex for processing sounds - auditory hallucinations
Basal Ganglia - responsible for motor movements - disorganised behaviour
HYPERdopaminergia rewards the brain and increases the firing rate in all these brain areas
Brain areas in the mesocortical pathway that correlate to schizophrenia
PFC - responsible for cognition and executive functioning - avolition, selective attention
Broca’s area - link to speech poverty
Motor cortex - catatonic behaviours
HYPOdopaminergia decreases the firing rate in these brain areas
Neural correlates explanation - defects in other neural areas
enlarged ventricles - studies have shown that people with SZ have reduced brain tissue and 15% more enlarged ventricles - the larger the more negative symptoms
reduction in size of temporal and frontal lobes - less myelin sheath in white matter between the PFC and hippocampus
lack of activity in the ventral striatum - responsible for anticipating reward from behaviour. those with SZ do not anticipate reward = avolition. decrease in the activity = increase in the negative symptoms
EVALUATION - of the neural correlates explanation of schizophrenia
STRENGTH - research support by a meta analysis which has investigated links between the ventricles and grey matter - analysed the results of 19 studies and found patients with SZ had a higher reduction in grey matter than healthy controls - this implies it is a biological disorder due to the degeneration of the neurons in the brain - however jt uses secondary sources with different methodological approaches so not possible to be certain that reduction in grey matter causes SZ
However even though there are criticisms, there are importantly implications for treatment as it raises the importance of early intervention to prevent the later stages - North American Prodrome Longitudinal study used several difference assessments including neuro imaging to predict who will develop psychoses such as SZ - this means early treatments can be used with at risk patients before it even develops therefore useful in preventing as well as treating - however raises ethical issues berger it is right to assess people with neuro imaging. Type 1 errors, incorrect restlent, labels and stigmas
