SZ - neuro explanation Flashcards
What is dopamine?
a neurotransmitter that plays a role in pleasure, motivation, and learning
What is SZ caused by according to the neurotransmitter explanation?
SZ is caused by excess dopamine activity (hyperdopaminergia)
What is excess dopamine caused by?
● Small amounts of the beta hydroxylase enzyme (breaks down dopamine), leading to a build-up of excess dopamine in synapses.
● A large amount of D2 receptors in the brain, so more dopamine messages get passed between neurons as dopamine has more opportunity to bind to receptors after diffusing across the synapse.
How are symptoms of SZ caused according to the neurotransmitter explanation?
- Low dopamine activity (hypodopaminergia) in the mesoCORTICAL pathway causes negative symptoms (flat affect: withdrawn, unsocial, lack of enjoyment in activities)
- Excess dopamine activity (hyperdopaminergia) in the mesoLIMBIC pathway causes positive symptoms (hallucinations and delusions)
sz neurotransmitter exp - serotonin
Serotonin regulates dopamine activity
- Excess serotonin leads to excess dopamine activity
- Negative symptoms may be caused by irregular serotonin activity
Evidence: Clozapine is a very effective antipsychotic because it reduces both + and - symptoms in most people
It works by binding loosely to dopamine receptors (D1, D2, D4), reducing dopamine activity AND serotonin receptors, reducing serotonin activity
sz neuro exp. - supporting evidence
evaluation
P: Supporting evidence
E: Carlsson reviewed research and found PCP ‘angel dust’ causes SZ-like symptoms. PCP is a powerful antagonist of NMDA glutamate receptors = ↓ Gluta = ↑ Dopa
T = valid explanation
sz neuro exp. - contrasting evidence
evaluation
P: Contrasting evidence
E: Depatie and Lal (2001) - found excess dopa doesn’t cause SZ in everyone
Non-psychotic pps were given dopa agonist which stimulates D2 receptors
= did NOT induce psychotic symptoms
= did NOT increase symptoms pps with SZ
T = less valid
sz neuro exp. - supporting evidence uses controlled lab cond. + objective measurements
evaluation
P: Supp. evidence uses controlled lab cond + obj measurements
E: Tenn’s study found that when rats were given amphetamine injections (which increase dopa) they showed behaviour similar to SZ
eg. erratic movements, oversensitivity to sensory stimulation
They were then given dopa antagonists (block dopa receptors) and found behaviours were reversed
T = evidence has high scientific status
sz. neuro exp - can’t explain all aspects of sz
evaluation
P: can’t explain all aspects of SZ
E: Tenn & Liebermann found negative symptoms can’t be explained.
Studies showing link between Amphetamines and SZ symptoms only explain positive symptoms NOT negative symptoms (social withdrawal, flatness of emo, memory and speech problems). This suggests dopa only plays a partial role
T = less valid, not a full explanation
sz. neuro exp - application (treatments)
evaluation
P: application to society (treatments)
E: Naheed and Green (2007) - review article and found antipsychotic Clozapine was the most effective drug treatment for ‘treatment-resistant SZ’
It blocks dopa and serotonin. Significant improvements in both positive and negative symptoms, quality of life, social functioning and suicidality
T = useful to society
sz. neuro exp - treatments don’t work for all
evaluation
P: treatments don’t work for all
E: Patel (2014) - antipsychotics don’t work for all individuals with sz
20% of pps with SZ show small improvement
45% experience only partial improvement and unacceptable side effects.
T = limited usefulness for society
sz. neuro exp - focus on nature side of the debate
P: Focus on nature side of debate
E: Owen (1978) - conducted post-mortem examinations in brains of ppl with SZ. Found higher density of dopa receptors than compared to those without SZ. Suggests more sensitivity to dopamine causes symptoms of SZ
T = detailed, scientific evidence
sz neuro exp. - reductionist, ignores nurture
evaluation
P: is therefore reductionist, ignores nurture
E: Howes and Kapur (2009) found neurotransmitter irregularities make people more vulnerable to SZ rather it being a direct cause Caused by an interaction between genetic predisposition and environmental risk factors (stress, trauma, drug use)
T = less valid
