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now we are going to talk about one of
the most important of the psychotic
disorders which is schizophrenia so what
is schizophrenia it's a psychiatric
disorder characterized by a
constellation of abnormalities in
thinking emotion and behavior here's
some facts about schizophrenia it
affects approximately 1% of people over
their lifetime men and women are equally
affected men present with the disorder
around 20 years of age whereas women
tend to present a little bit older
around 30 years of age it's very rare
for someone to present with symptoms of
schizophrenia before age 15 or after the
age of 45 here's a question for you what
season of birth is associated with
higher rates of schizophrenia winter
birth and there are a few thoughts about
why this's may be because environmental
stressors such as cold weather
nutritional deficiencies or exposure to
infectious agents during this time of
year occur there are a lot of different
hypotheses in terms of the pathogenesis
of schizophrenia the most prominent of
which are the dopaminergic pathways I
posses so being that there is a
disruption in either the mesolimbic
pathway which creates what we call
positive symptoms of schizophrenia the
mesocortical pathway which produces
negative symptoms the nigrostriatal
pathway which is involved in
extrapyramidal symptoms and also tardive
dyskinesia or the tubero infundibular
pathway involved in hyperprolactinemia
we'll go through each of these in a
little bit more detail now the mezzo
limbic pathway plays a key and complex
role in our motivation emotions
reward and positive symptoms therefore
of schizophrenia the mezzo cortical
pathway is relevant to the physiology of
cognition and executive function this is
in the dorsolateral prefrontal cortex
emotions and effect are involved in the
ventromedial prefrontal cortex and
hypofunction of this pathway might be
related to the cognitive and negative
symptoms that are seen in schizophrenia
the striatal pathway contains
about 80% of the brains dopamine a very
important neurotransmitter that we think
is highly dysregulated and individuals
who have psychotic disorders especially
schizophrenia the nigrostriatal pathway
is involved in motor planning and
dopaminergic neurons stimulate
purposeful movements dopaminergic
projections in the tubero infundibular
pathway influence the release of
prolactin the dopamine is released into
the portal circulation connecting the
median eminence with the anterior
pituitary gland the role of dopamine
release in the tubero infundibular
pathway is to tonic ly inhibit prolactin
release and so when this pathway is
disrupted that's why we think people get
hyperprolactinemia other causes of
schizophrenia include the downward drift
hypothesis which is where individuals
who are affected by the illness tend to
follow a downward trajectory in terms of
not always being very highly educated
not being able to sustain stable jobs
and then basically deteriorating and
drifting downward in the socio-economic
stratosphere which then perpetuates
meeting someone in producing preneur
susceptible to the illness other
neurotransmitters that are implicated
include serotonin histamine
norepinephrine
and GABA and glutamate you might ask why
is glutamate an excitatory amino acid
neurotransmitter of any interest in
schizophrenia research the answer is
that the NMDA glutamate receptor is
blocked by PCP and produces a clinical
syndrome similar to schizophrenia
including the positive and negative
symptoms as well as formal thought
disorder here's a question as well what
are the psychiatric indications for
neuroimaging studies you want to do
neuroimaging studies such as a CT scan
of the brain or MRI in any person who's
presenting with a first-time psychotic
episode again it's very important to
rule out medical problems you also want
to do had imaging when somebody is
acutely confused if there's dementia of
unknown cause prolonged catatonia if
there is a movement disorder of unknown
origin or a personality change and
someone over the age of 55 these are all
indications to do head imaging another
question to consider here what is the
most consistent functional neuroimaging
study finding in people with
schizophrenia
the answer is hypofrontality
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