Electroencephalography (EEG) uses electrodes on the scalp to measure electrical activity from the brain. Quantitative spectral EEG investigates several waveforms, and so the activity can be measured, but EEG also gives rise to event related potentials (ERP), which measure the EEG activity directly evoked by a stimulus, often using cognitive or perceptual stimuli. Error-related negativity is a response-locked ERP that has been associated with monitoring of actions and detecting errors. Error-related negativity is typically followed by the error positivity component. In contrast to error-related negativity and error positivity, feedback negativity is elicited by externally provided feedback about positive rather than negative outcomes. Spectral waveforms measured by EEG include delta waves (up to 4 Hz), which are slow waves with high amplitude; theta waves (4-7 Hz), which are also slow waves; alpha waves (8-12 Hz), which occur mostly at rest, beta waves (12-30 Hz), which are fast waves with low amplitude, occurring during times of alert concentration, and gamma waves (30-100+ Hz) which occur during certain cognitive and motor functions. One example of an ERP is the P300 wave, which is measured primarily over the parietal lobe and is used as a measure of cognitive function. EEG is also used to measure electrical activity during sleep, to identify disruptions to sleeping patterns.

What is the evidence for EEG?

Moderate to high quality evidence finds theta and delta wave activity are increased and P300 amplitude is decreased in people with schizophrenia. Moderate quality evidence also finds increased beta wave activity and decreased alpha wave activity.

Moderate to high quality evidence finds a large effect of reduced error-related negativity in people with psychosis and a medium-sized effect in those at risk of psychosis. There were no differences in error positivity or feedback negativity.

Moderate quality evidence finds people with schizophrenia had large effects of shorter total sleep time, more awake time, longer sleep onset latency, and lower sleep efficiency. There were medium-sized effects of increased stage 1 sleep, decreased stage 4 sleep, decreased slow wave sleep, and decreased REM latency. There were small effects of decreased stage 3 sleep and increased REM duration. Moderator analyses found medication-naïve patients had shorter total sleep time, longer sleep onset latency, decreased sleep efficacy, and longer awake time. Patients recently withdrawn from antipsychotics had shorter total sleep time, longer sleep onset latency, decreased sleep efficacy, longer awake time, increased stage 1 sleep, decreased stage 2, 3, and 4 sleep, decreased slow wave sleep and shorter REM latency. Patients on antipsychotics had significantly longer sleep onset latency, increased stage 2 sleep, and decreased total REM sleep.

October 2020

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Smooth pursuit eye movement is a visual tracking reflex evoked by a smoothly moving target, usually elicited by stimuli presented on a computer monitor. Deficits in smooth pursuit and an excess of ‘jerky’ eye movements were one of the earliest reported phenotypes associated with schizophrenia, and smooth pursuit has since been identified as a candidate endophenotype (phenotype with a clearer genetic connection) for schizophrenia. The aim of the smooth pursuit reflex is to maintain the image of the moving target on the fovea, the region of the retina with the highest density of photoreceptors. The neural pathways involved in generating smooth pursuit are a complex network from the cortical visual pathways through to the brainstem ocular motor nuclei (III, IV and VI), and consequently an alteration in smooth pursuit performance may not in itself shed light on the actual nature of the dysfunction. Components of smooth pursuit which are quantified include gain in the open and closed loops, as well as rates and amplitudes for both intrusive and anticipatory saccades (fast eye movements). Closed loop gain is an index of temporal synchrony of the eye and the target during pursuit, and is estimated as the ratio of the respective velocities. Open loop gain is the average acceleration during the initiation of pursuit, in the first 100ms. During this period there is no visual feedback and so the movement is solely a result of visual motion signal input. Spontaneous saccades can occur during smooth pursuit: these can either be anticipatory saccades which facilitate movement towards the target, such as reflexive visually guided saccades; or intrusive saccades, which interrupt the smooth tracking of the target, such as catch-up saccades, back-up saccades, and memory-guided saccades.

What is the evidence on eye movement dysfunction?

Moderate to high quality evidence suggests reduced eye tracking performance in people with schizophrenia compared to controls, particularly in maintenance (closed loop) gain. Moderate quality evidence also suggests increased saccadic intrusion during eye tracking, with the effect largest for leading saccades and catch-up saccades. High quality evidence suggests relatives of people with schizophrenia also show impairment in closed loop gain during smooth pursuit eye movement. Moderate quality evidence suggests they show increased error rate of visually and memory guided saccades, impairment in fixational stability, and increased intrusive anticipatory saccades during smooth pursuit eye movement.

October 2020

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MEG uses a helmet-shaped device containing MEG sensors (gradiometers) to noninvasively measure the magnetic fields produced by neural activity of the brain. MEG is able to localise the source of neural activity to particular brain regions, represented as positive and negative charges (dipoles), with greater accuracy than EEG, which is a measure of the electrical fields produced by neural activity. MEG can be used to measure continuous resting-state brain activity (spontaneous MEG), but also to assess event-related changes in brain activity. Spontaneous MEG reflects neural activity in particular brain regions and across a range of frequencies. Delta frequency (up to 4 Hz) is slow wave activity normally seen during deep sleep; theta frequency (4 to 7 Hz) is often seen during drowsiness and early stages of sleep; alpha activity (8 to 12 Hz) commonly occurs during a state of relaxed wakefulness, particularly when eyes are closed; beta frequency (13 to 30 Hz) of low amplitude occurs during intense concentration and mental activity; and gamma frequency (30 to 80+ Hz) occurs during certain cognitive and motor functions. Change in activity is assessed as a dipole density, which measures the representation of each type of wave within a particular region.

What is the evidence on MEG?

Moderate to low quality evidence suggests increased bilateral delta and theta wave activity in the frontal, temporo-parietal and occipital cortices of people with schizophrenia, which appear to be particularly associated with positive symptom severity. Beta activity was reportedly increased in frontal and temporo-parietal regions, and changes in alpha and gamma activity are unclear.

October 2020

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MMN is an auditory event-related potential that is generated when a stimulus feature deviates from the regularity of previous auditory stimuli. This deviance can be a simple physical characteristic, such as tone duration, intensity, frequency or location; or more abstract presentation characteristics, such as a lower tone in a series of ascending tones. In this way, MMN generation relies on the creation of an auditory (echoic) memory trace for the preceding tones, in order to identify the subsequent deviance. MMN is thought to be an automatic, pre-attentional process and functions as an index of auditory discrimination and echoic memory integrity. MMN is observed as the difference in ERP wave response to the standard stimuli and the deviant stimulus. Larger differences between standard and deviant stimuli and lower probability of deviant occurrence are both associated with larger MMN amplitude.

What is the evidence on MMN?

Moderate to high quality evidence finds a large MMN deficit in people with schizophrenia compared to controls, which was largest in studies of chronic patients, in studies using duration deviants rather than frequency or intensity deviants, and when tones were unattended rather than attended. Moderate to low quality evidence finds no associations between MMN deficits and symptom severity.

Moderate quality evidence finds a medium-sized deficit in duration deviants, but not in pitch deviants, in people with first-episode psychosis. There was a medium-sized MMN deficit in people at clinical high risk of schizophrenia (people with subclinical symptoms), and a small MMN deficit in people at familial high risk of schizophrenia (people with a first-degree relative with schizophrenia).

October 2020

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The N100 is a negative waveform that peaks at approximately 100 milliseconds after stimulus presentation. Its amplitude is measured using electroencephalography (EEG) and may be dysfunctional in people with schizophrenia who show an inability to “gate” or inhibit irrelevant sensory information, ultimately leading to conscious information overload. To test this, paired auditory clicks are presented, separated by a short interval, usually of 0.5 seconds. The first click initiates or conditions the inhibition, while the second (test) click indexes the strength of the inhibition. An absence of a reduced response to the second stimulus is interpreted as a failure of inhibitory mechanisms, postulated to represent a defect in sensory gating.

What is the evidence for N100 event-related potential?

Moderate to high quality evidence finds a medium-sized reduction in N100 amplitude to the first stimulus, but not to the second stimulus. Review authors suggests this reflects a deficit in processing of auditory salience rather than in inhibition.

October 2020

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The N170 wave is an event-related brain potential (ERP) measured using electroencephalography (EEG). The N170 is a negative waveform that peaks at approximately 170 msec after stimulus presentation. It is observed at occipitotemporal sites and with greater amplitude over the right hemisphere. The N170 ERP is observed in response to a variety of facial stimuli, so it may reflect a neural mechanism for detection of human faces.

What is the evidence for N170 event related potential?

High quality evidence shows people with schizophrenia have a medium-sized reduction in N170 amplitude in response to face stimuli when compared to controls’ response. There were no differences in effect size according to different face stimuli (e.g. emotional vs. non-emotional or no judgment).

October 2020

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The N250 wave is an event-related brain potential (ERP) measured using electroencephalography (EEG). The N250 is a negative waveform that peaks at approximately 250 msec after stimulus presentation. It is observed at fronto-central sites in response to face stimuli, and so it may reflect a neural mechanism for detection of human faces.

What is the evidence for N250 event related potential?

High quality evidence shows people with schizophrenia have a medium-sized reduction in N250 amplitude compared to controls during exposure to face stimuli.

October 2020

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The N400 wave is an event-related brain potential (ERP) measured using electroencephalography (EEG). N400 refers to a negativity peaking at about 400 milliseconds after stimulus onset. It has been used to investigate semantic processing, which may be dysfunctional in schizophrenia. Semantic processing can be separated into two stages; early automatic semantic activation without the involvement of attention, and late contextualisation that is influenced by attention. The semantic priming effect refers to the reduction of reaction time to a word (e.g. table) when it is preceded by a semantically congruent context (e.g. chair) as opposed to a semantically incongruent context (e.g. lake). With a relatively short stimulus onset asynchrony (SOA; less than 500 milliseconds) in word or picture-pair studies, the priming effect is mainly attributed to early automatic semantic activation. With a long SOA (>500 milliseconds), the priming effect is mainly attributed to late contextualisation processes.

What is the evidence on N400 event-related potential?

High quality evidence shows people with schizophrenia have a medium to large increase in N400 peak latency when compared to people without schizophrenia. They also have a small to medium-sized decrease in N400 amplitude in congruent conditions but not in incongruent conditions. These results are largest in tasks involving long stimulus onset asynchrony. Patients show a decreased N400 semantic priming effect in both short and long stimulus onset asynchrony conditions.

October 2020

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The P100 is a positive waveform that peaks at approximately 100 milliseconds after stimulus presentation. The P100’s latency and amplitude vary with aspects of selective attention or stimulus encoding. Latency is considered a measure of stimulus classification speed, and amplitude is proportional to the amount of attentional resources devoted to the task and the degree of information processing required.

What is the evidence for P100 event-related potential?

Moderate to high quality evidence finds a medium-sized reduction in P100 amplitude with neutral and happy face stimuli, but not fearful face stimuli in people with schizophrenia compared to controls.

October 2020

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The P200 wave is an event-related brain potential (ERP) measured using electroencephalography (EEG). P200 refers to a spike in activity approximately 150 to 250ms following presentation of a target stimulus that is most commonly auditory, although response is also obtained following somatosensory and visual events. The P200’s latency and amplitude vary with aspects of selective attention or stimulus encoding. Latency is considered a measure of stimulus classification speed, and amplitude is proportional to the amount of attentional resources devoted to the task and the degree of information processing required. Amplitude and latency may be measured using tasks using ‘standard’ and ‘oddball’ stimuli, where the subject is asked to react only to ‘oddball’ target stimuli that are hidden as rare occurrences amongst a series of more common, ‘standard’ stimuli.

What is the evidence on P200 event-related potential?

Moderate quality evidence suggests a small reduction in P200 amplitude and latency at the central midline electrode during standard stimuli conditions, and a small to medium increase in amplitude and latency at the frontal, central and parietal electrodes during oddball stimuli conditions in people with schizophrenia compared to people without schizophrenia.

October 2020

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