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An acute schizophrenic group had less alpha power, this change being confined largely to the temporal areas. A chronic outpatient sample showed less alpha and beta power, while chronic long-stay schizophrenic patients had an excess of delta power.

One prominent finding is an increased frequency of EEG records reflecting high activation levels, as judged by reactivity of the EEG upon opening the eyes, among schizophrenic patients in an unmedicated state (99). Consistent with hyperactivation are quantitative results showing that EEGs of schizophrenic subjects have lower alpha power, increased variability of frequency, and higher wave symmetry than comparison subjects (99). Given that excesses in both slow and fast EEG activity have been reported, however, Shagass (99) suggests that dysregulation of brain activity in schizophrenia might be a more basic problem than hyperactivation per se.

Several topographic EEG studies have found evidence of excessive slow activity (delta) in frontal areas (e.g., 48,80). This is conceptually consistent with PET and regional cerebral blood flow evidence of reduced frontal activity in at least some schizophrenic patients and increased frontal delta activity was correlated within schizophrenic samples with PET hypofrontal metabolic patterns (48)

The most common ERP paradigm has examined P300 (P3) amplitude and latency in a situation in which an occasional, unpredictable physical change in a stimulus occurs within a series of identical stimulus presentations (the "oddball" paradigm). The oddball stimulus may, for example, differ from the repeated standard stimulus in pitch or duration. The P300 response in this situation is an index of cortical response related to recognizing and processing the significance of the relatively rare stimulus. Schizophrenic patients were first found to show reduced P300 amplitude in this paradigm a little more than 20 years ago, and reduced P300 amplitude has been among the most robust of ERP results for schizophrenia

P300 reduction in schizophrenia appears to be linked to the presence of background stimuli that make the identity of the next stimulus uncertain. It occurs even when experimental instructions do not call for motivated effort, and in some studies has been significantly related to the level of negative symptoms (32,89). P300 paradigms have also bolstered the evidence that schizophrenic patients have deficits in maintaining attention and show inappropriate allocation of attentional resources to novel distracting stimuli (32,79).

Another ERP paradigm applied to schizophrenia has focused on endogenous negativity in the waveform associated with effortful or attention-demanding processing of information (104). This paradigm records ERPs that occur to very brief visual letter arrays in a simple reaction time task (without the need to discriminate letters) and compares them to ERPs that occur to the same visual letter arrays when the subject is instructed to discriminate whether one of two letters is included among others in the arrays. The latter situation, called the Span of Apprehension task, has been shown to detect early visual processing abnormalities in schizophrenic patients in remitted and psychotic states. It is hypothesized to be sensitive to a genetic vulnerability factor relevant to schizophrenia (5). By subtracting the ERP for the simple reaction time condition from the ERP for the Span of Apprehension condition, the electrophysiological response associated with the visual discrimination process has been examined (104). Through this subtraction procedure, Strandburg and colleagues have shown that schizophrenic patients, including schizophrenic children, produce a significantly smaller Span elicited negativity (SEN) than normal subjects (104).

An early positive ERP component, P50, has been the focus of substantial recent research as a possible index of a vulnerability factor for schizophrenia. A measure of sensory gating during the initial processing of stimuli can be obtained by examining the extent to which P50 amplitude to a simple auditory stimulus is reduced when another simple auditory stimulus occurs immediately before it (37). The concept of a sensory or sensorimotor gating process has been central to work involving P50 and to work with a paradigm that we discuss in the next section, prepulse inhibition of the startle blink response.

Acute schizophrenic patients in the early stage of their psychosis often describe vivid experiences suggestive of an impaired ability to gate irrelevant stimuli and focus on relevant stimuli (78). For example, one patient reported, "I am speaking to you now but I can hear noises going on next door and in the corridor. I find it difficult to shut these out and it makes it more difficult for me to concentrate on what I am saying to you"

EDA research with schizophrenia patients has focused primarily on phasic SCR orienting responses to innocuous stimuli (e.g., moderately intense tones without task significance). Approximately 40%–50% of schizophrenic patients fail to exhibit any SCR orienting responses to innocuous tones, compared with only 5%–10% in the normal population (7,22,123). In contrast to the SCR "non-responders", the remaining 50%–60% of the patients do respond with SCRs to innocuous tones but also show abnormally high tonic arousal. Thus, there appear to be at least two well documented EDA abnormalities in schizophrenia: (1) SCR hyporesponsiveness to innocuous stimuli and (2) SCL and NS-SCR hyperarousal (22,23).

http://www.acnp.org/g4/GN401000119/CH117.html

http://www.guardian.co.uk/science/2010/jul/05/brain-scans-predict-schizophrenia

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August 2011

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