Conclusions from PET
Studies
• Schizophrenia is not a disease of
a single brain region
• Areas of abnormality vary
depending on the task and the
nature of current symptoms
• Schizophrenia affects distributed
circuitry throughout the brain
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fMR Studies
The fastest-growing
field in neuroimaging
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The fMR Blood Flow
Signal
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Verbal Fluency
Patients
Controls
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The N-Back Task for fMR
Experimental Task (2-Back): Remember the Probe and Monitor for It
Comparison Task: Look for the S
Look for the S
A
2-Back Task
L
B
C
S
Target
D
E
x
Probe
G
x
Target
K
A
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2-Back Task in Normals
•Bilateral
dorsolateral
frontal
•Bilateral
parietal
•Anterior
cingulate
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2-Back Task in Schizophrenia
(unmedicated)
•Blood flow markedly
decreased or absent
in regions used by
normals
•Main activation is
anterior cingulate
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Neuropsychology
Cognitive Psychology
Cognitive
Neuroscience
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Classical
Neuropsychology
• Derived from the study of
neurology patients with specific
brain lesions
• Develops tests that are sensitive
to detecting those lesions
• Pattern of test performance used
to determine the site of the
lesion
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Cognitive
Neuropsychology/
Neuroscience
• Emphasizes cognitive processes
rather than test performance or lesion
location
• Seeks to find dissociations between
types of cognitive processes (e.g.,
episodic vs semantic memory)
• Assumes that mental processes are
based on fundamental cognitive
“modules” that will map onto discrete
brain systems
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Methodological Issues
• Absence of any specific
lesion in schizophrenia
• Effects of medication on test
performance
• Effects of institutionalization
• Effects of envirnomental
stimuli or distractors
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Generalized Deficits in
Schizophrenia
• Patients perform poorly on
almost all cognitive tests
• Evidence to date does not
support a lesion in a specific
brain region (neuropsychology)
or an impairment in a specific
cognitive system (cognitive
neuroscience)
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Cognitive Studies:
Faculties
•
•
•
•
•
Attention
Memory
Language
Executive function
Very little evidence supports a
specific dysfunction in attention,
memory, or language in
schizophrenia—all are impaired
• These specific cognitive faculties
could be impaired due to a problem in
executive function
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Lobology: Evidence from
Cognitive Tests
•
•
•
•
•
Occipital: little evidence
Parietal: some evidence
Temporal: more evidence
Frontal: even more evidence
However…these inferences are
based on the (potentially
inapplicable) assumptions of
neuropsychological lesion
studies
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Models of Signs and
Symptoms: Cognitive
Neuropsychiatry
• Attempts to explain signs
and symptoms, rather than
schizophrenia in general
• E.g., negative symptoms,
positive symptoms, social
interactions
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Negative Symptoms
• Poverty of speech, affective
blunting, motor retardation share
a common feature—lack of
spontaneous behavior or “willed
action”
• Could be explained on the basis
of abnormalities in the frontostriatal “functional loop”
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Hallucinations
• Multiple cognitive explanations,
such as…
• The experience of inner speech
as alien or exterior
• Due to a failure in selfmonitoring, so that speech or
thoughts occur without
awareness of prior intention, and
are therefore perceived as alien
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Persecutory Delusions
• Result from the patient making
incorrect inferences about the
intentions of others or the
meaning of stimuli in the external
environment
• Due to a failure of the ability to
infer the beliefs or intentions of
others (“theory of mind” or
“mentalizing”)
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Modern Cognitive Models
• A disease with no
consistent
neuropathology
• A disease that arises
from dysfunctional
neural circuits (no
obvious lesion)
• A disease that is
defined by cognitive
impairment
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Some Modern Cognitive
Models
• Working memory/
representationally guided behavior
• Information processing/sensory
gating
• Synchrony of thought/cognitive
dysmetria
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Working Memory
• The ability to hold information online and
perform mental operations using it
• Permits individuals to base behavior on
internally held plans rather than being
driven by external stimuli
• Can explain most symptoms—e.g., the
inability to correctly reference sensory
experiences could lead to delusions and
hallucinations
• Is supported by multiple imaging and
cognitive studies
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Sensory Gating
• A problem in filtering or gating
information
• Leads to the subject experience
of being bombarded by stimuli
• Explains most symptoms—e.g.,
confusion of internal and
external stimuli would cause
delusions and hallucinations
• Supported by neurophysiological
studies of prepulse inhibition
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Cognitive Dysmetria
• A defect in coordinating mental activity
• Due to disturbed functional connectivity
between the cortex and subcortical
regions (thalamus and cerebellum)
• Leads to functional and cognitive
misconnections
• Explains diversity of symptoms (e.g.,
misconnecting a perception and its
meaning might lead to delusions and
hallucinations)
• Supported by functional imaging studies
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