biological explanation of schizophrenia

8/3/2019 Biological Explanation of Schizophrenia

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Types & Symptoms of Schizophrenia

Paranoid

DisorganisedCatatonic

Undifferentiated

Residual


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Types & Symptoms of Schizophrenia

Paranoid Delusions, hallucinations,negative symptoms

DisorganisedAimless, disorganised

behaviour; rambling, incoherentspeech

Catatonic Motor abnormality unmovingstrange posture or flailing limbs

Undifferentiated So many symptoms cannot becategorised or not enoughsymptoms

Residual Symptoms present before butnot now, however, negativesymptoms now


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Biological Explanation of

Schizophrenia


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Lesson Objectives

By the end of the lesson you will beable to:

Describe the four biologicalexplanations of schizophrenia.

Evaluate these four explanations.


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Biological Explanations

Who can name the four different biologicalexplanations?

Genetic factors

Biochemical Factors

Brain dysfunction

Viral Infection


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Genetic factors

Family Studies:Biological relatives (Gottesman) 1991found Schizophrenia is more common inthe biological relatives of a schizophrenic.

The closer the degree of relatedness thegreater risk what do we mean????

Identical twins, fraternal twins then childrenare the top three as they are closer related.


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Genetic factors

Identical twins:

Research hasconsistently shownidentical twins havearound 48% risk ofdevelopingschizophrenia if theother twin has.

Why is this? Because identicaltwins share 100%

genes.

Fraternal twins:

Only have a 17%chance

Why because theyshare only 50% samegenes (Janicak at al2001).


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Genetic factors

Adoption studies:

Kety et al 1988 found 14% of biological

relatives of adoptees with schizophreniawere classified as schizophrenic, whereasonly 2.7% of their adoptive relatives werefound to be.

Shows more emphasis on biologicalcauses of schizophrenia.


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Genetic factors

Insights from molecular biology

Miyakawa et al (2003) created geneticallymodified schizophrenic mouse by switching off a

specific gene in the brain responsible for makingthe chemical calcinerurin.

Mice showed abnormalities e.g. social withdrawal

mirrored behaviour of schizophrenic patients.

Miyakawa et al (2003) studied DNA families withschizophrenia, found those who had it were morelikely to have defective version of the gene.


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Biochemical Factors

The dopamine hypothesis

Dopamine = transmitter in the brain.

Schizophrenics thought to have more D2

receptors therefore more dopamine binds tothe receptors and cause more neurons to fire.

Dopamine is linked to

attention and may lead to

problems with attention which

is thought to be found in people

with schizophrenia (Comer 2003)
http://www.coolschool.ca/lor/BI12/unit12/U12L04/Synapse.gif


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Biochemical Factors

Evidence supporting dopaminehypothesis:

Antipsychotic drugs

1950s identified Phenothiazines these drugs bind to the D2receptors and block thetransmission of nerve impulsestherefore reducing the attentionaldeficit in schizophrenics.


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Biochemical factors

Parkinson's Disease

Low levels of dopamine activity are found insufferers of Parkinson's disease (adegenerative neurological disorder).

Parkinsons sufferers taking the drug L-dopato raise their dopamine developedschizophrenic type symptoms (Grilly 2002)


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Brain Dysfunction

Enlarged ventricles

Brain imaging techniques have identifiedschizophrenics have enlarged ventricles (about 15%

bigger than normal), cavities in the brain that supplynutrients and remove waste (Torrey 2002).

Such individuals tend to display negative rather thanpositive symptoms and have greater cognitive

disturbances and poorer response to traditionalantipsychotic drugs (Bornstein et al 1992).

Enlarged ventricles may be a result of poor braindevelopment or tissue damage. These problems lead

to the development of schizophrenia.


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Brian Dysfunction

Specific Brain abnormalities:

Meyer-Lindenberg et al 2002 examined

brain activity in schizophrenics engaged ona working memory task. Their prefrontalcortex showed reduced activation,reflecting poor performance.

Dopamine levels were elevated suggestingdysfunction of the prefrontal cortex is linkedto dopamine abnormalities.


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Viral Infections

Research has suggestedschizophrenia is linked to exposure toviruses before birth.

Such viruses may remain dominantuntil puberty when hormonal changesactivate the virus and causeschizophrenic symptoms (Gheradelliet al 2002).


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Viral Infections

Evidence for viral theory:

Significant number of people with

schizophrenia are born during winter whenvirus exposure is high (Torrey 2000).

Mothers of schizophrenia are more likely tobe exposed to influenza virus duringpregnancy (de Messias et al 2001).


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Viral Infections

Evidence for viral theory:

Identical twins research identified

fingerprint abnormalities. Fingerprintsdevelop in second trimester of pregnancywhen the foetus is at more risk fromviruses thus these abnormalities could

indicate viral infection during this periodcausing them and predisposing them toschizophrenia (Comer 2003).


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Biological Approach

Has much support

Doesnt rule out psychological factors

Current thinking isdiathesis-stressrelationship.

Diathesis-stress relationship = there are

biological predispositions (the diathesis) forSchizophrenia THAT only develops into thedisorder if significant psychological stressors(stress) are present. (Gottesman and Riley),2003

biological explanation of schizophrenia

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