PSYC 2800 Study Guide - Final Guide: Phenylalanine Hydroxylase, Deep Brain Stimulation, Intellectual Disability

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20 Apr 2012
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Neurobehavioural Disorders
Causes of Abnormal Behavior
Evidence for brain abnormalities in organic-neurological disorders is
straightforward, and the causes are generally known
Genetic errors (e.g., Huntington’s disease)
Progressive cell death (e.g., Alzheimers disease)
Rapid cell death (e.g., stroke)
Loss of neural connections (e.g., multiple sclerosis)
Far less is known about the causes of behavioral/psychiatric disorders
(depression, schizophrenia, etc.), but there must be some abnormality in
brain structure or activity(involve changes emotions, motor activity, etc.),
but can’t pinpoint causes.
Investigating the Neurobiology of Behavioral Disorders
Phenylketonuria (PKU)
Test for it at birth, easy
Behavioral disorder caused by elevated levels of the amino acid
phenylalanine in the blood
Results from a defect in the gene for the enzyme phenylalanine
hydroxylase (lack this enzyme). Buildup of phenylalanine
resulting in mental retardation
Easily fixed, don’t eat food with phenylalanine
Major symptom: severe mental retardation
Unlike PKU, most disorders do not involve a single genetic
abnormality and the underlying causes are largely conjectural
Challenges in Diagnosis
It is difficult diagnose behavioral disorders
People are seldom objective observers of their own behavior or that
of a loved one
The patient and their loved ones may be selective in what they
notice
Ex: autism. Don’t want to say something is wrong, just delayed.
People are seldom specific in identifying symptoms
Memory deficits? Say forgetting things but not specific deficit.
Evaluators have their own conceptual biases, which may influence
the questions that they ask and the information that they gather. May
see bunch of different people who view us through different
perspectives and thus have different diagnosis.
Investigating the Neurobiology of Behavioral Disorders
The complexity of the nervous system makes it very difficult to research
Heninger (1999)
There is no clear evidence of a single receptor system with a specific
relation to a specific behavior
Ex: Dopamine not just involved in one thing (reward) but also
retention, etc.
Animal models of behavioral disorders are useful, but they provide an
oversimplified view of the neurobiology of such disorders. Can’t model
things perfectly
Ethical limitations to test on humans
Identifying and Classifying Mental Disorders
Epidemiology
The study of the distribution and causes of diseases in human
populations. How prevalent it is in a pop.
Ex: How many women in Ottawa have breast cancer
DSM
The Diagnostic and Statistical Manual of Mental Disorders, the
American Psychiatric Association’s classification system for psychiatric
disorders (see Table 16-3)
Current edition is DSM-IV-TR, DSM-V slated for 2014
Checklist of criteria for disorders
Not perfect method, people meet and vote on what gets into DSM
In 70’s homosexuality was a mental disorder
Psychiatric disorders are to some extent arbitrary and depend on prevailing
cultural views
Conflict about new disorders going into new DSM
The Use of Brain Imaging
Brain imaging techniques are currently not used to diagnose mental
disorders
To be clinically useful, imaging tools must be sensitive enough to detect
unique features of brain disorders and specific enough to rule out similar
conditions. Now can only see gross changes in brain
Still, imaging is shedding new light on behavioral disorders
Ex: early onset (adolescent) schizophrenia = loss of grey matter
Treatments for Disorders
The long-term prospects for curing organic or behavioral disorders on the
macro level depend on the ability to treat structural and biochemical
abnormalities at the micro level (genes, receptor changes, etc.). Must affect
micro level to see longterm changes.
Ultimate clinical problem:
Apply the knowledge of behavioral neuroscience to generate
treatments that can restore a disordered brain (and mind) to the
range of normalcy
Nosology (naming) precedes etiology (cause): how do we treat a
disorder when we don’t know what causes it? Name disease before
we know what causes it so may be clustering groups of symptoms
that may be different diseases all together.
How do we treat disorder when don’t know cause? Give treatments
(address symptoms) instead of a cure
Neurosurgical Treatments
Either damage or stimulate some dysfunctional area of the brain
Deep brain stimulation (DBS) Neurosurgery in which an electrode is semi-
permanently implanted in the brain stimulate a targeted area with a low-
voltage electrical current to facilitate behavior
Artificially stimulate
Used to treat Parkinson’s and depression (when anti depressants
don’t work)
Neurosurgical Treatments
Stem cell Therapy
Aims to return a dysfunctional brain region back to its embryonic
state and regrow a normal region