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 GABA A 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