Download The role of synchronous gamma-band activity in schizophrenia

The role of synchronous
gamma-band activity in
schizophrenia
Jakramate
2009 / 01 / 14
Keywords
Schizophrenia: a mental disorder characterized by abnormalities in the
perception or expression of reality, i.e. delusion and hallucination
Neural synchrony: synchronous oscillations of membrane potentials in a
network of neurons
Gamma-band: Oscillation in high-frequencies band
Recent researches believe that there exist the relationship between
impairment of neural synchrony, especially in gamma band and
cognitive deficits found in schizophrenia
Synchrony impairments are
temporal incorrect (delay)
phase shift
amplitude reduction
The result of many experiments suggest that schizophrenia patients
may have abnormalities in establishing and maintaining both
oscillation amplitude and phase synchronization to simple auditory
and visual stimuli
Schizophrenia
Schizophrenia is a psychiatric diagnosis that describes a mental
disorder characterized by abnormalities in the perception or expression
of reality
Symptoms of the disease can be classified in two categories
Positive
auditory hallucinations
Hallucination: Sensory perception without external stimuli
paranoid delusions
Thought disorder
Odd behavior
Negative
Social withdrawal
Lack of motivation
Causes
Neural & Drug
Genetic, Social, Psychological
Neural synchrony
Neural synchrony is the simultaneous / synchronous
oscillations of membrane potentials in a network of neurons
connected with electrical synapses
It is considered by some theorists to be the neural correlate
of consciousness.
It can be referred to as synchronous oscillatory activity or
simply oscillatory activity
Neural synchrony (cont.)
Oscillatory activity in local area tends to occur at higher
frequencies (gamma band: >30Hz)
Those activities in anatomically distant but functionally
closely related brain areas occur at lower frequencies
the beta (12-30Hz)
The alpha (8-12Hz)
The theta (4-8Hz)
Neural synchrony (cont.)
There are 2 forms of oscillatory activity
Spontaneous oscillation
Uncorrelated with the occurrence of any stimuli
Event-related oscillation
Evoked
tightly time- and phase-locked to the onset of stimuli
Induced:
Not phase-locked
Related to attention, cross-modal binding, maintenance of
working memory contents
Method of examining neural
synchrony
electroencephalogram(EEG) &magnetoencephalography
(MEG)
Analyze spectral power of the oscillatory activity in the short
range (within 1 cm)
Analyze phase differences of the oscillatory activity between
neural assemblies that are farther apart ( > 2 cm.)
Intertrial phase-locking uses to measure temporal variation of
incoming stimuli in case of evoked oscillation
Single trial analysis in case of induced oscillation
Neural synchrony in
schizophrenia
There is evidence of impaired gamma-band oscillations from
studies probing
Early sensory system (auditory & visual)
More cognitive event-related paradigms
In early sensory deficits test, patient
failed to show evoked EEG oscillation
exhibit delays of phase synchronization
exhibit poor P50 suppression in P50 click paradigm which
related to phase-locked in gamma-band activity
failed to show good result in backward masking test which
related to induced gamma-band activity
Neural synchrony in
schizophrenia (cont.)
In cognitive processing deficits test in which subject has to
perform higher-level auditory and visual processing,
researcher found that
Patient …
exhibits the reduction of gamma spectral power
exhibits poor phase synchronization
show the reduction of both evoked and induced gamma-band
activities
In working memory task, patient showed high gamma-band
activity independently of workload while activity in normal
people only increased when workload increased
Neuropharmacological mechanism
& oscillatory activity
Many neurotransmitters have been linked to affected gamma band
oscillatory activity
Promoting
Dopamine polymorphism can modulate evoked oscillation
GABAA is important for eliciting gamma-band oscillatory activity
Nicotine has also been used to relief the symptom of schizophrenia
Demoting
Ketamine can abolish Gamma-band oscillations
Amphetamine (Dopamine agonist) tend to produce psychotic
symptom