Attenuation of beta and gamma oscillations in schizophrenia spectrum patients following hand posture perturbation
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Several electroencephalographic (EEG) studies in schizophrenia report that the patients have reduced evoked gamma activity following visual and auditory stimulation. Somatosensory gamma activity has not previously been examined. It has been suggested that a dysfunction basic to schizophrenia spectrum traits would involve proprioceptive information processing and this has recently been supported by the finding of diminished latency of early proprioceptive evoked potentials in a sample of chronic schizophrenia patients. The proprioceptive stimulus used previously, and presently, consisted of an abrupt increase of weight on a hand-held load. Eighteen first-time admitted schizophrenia spectrum patients and 18 healthy matched comparison subjects were included. Proprioceptive evoked potentials were recorded as 64-channels EEG for 120 trials in two runs differing in sequence. Contra-lateral evoked beta (latency 90 ms, frequency 21 Hz) and gamma (latency 70 ms, frequency 32 Hz) oscillations were attenuated in the patient group. The healthy comparison subjects had increased gamma amplitude in the left hemisphere in the regular sequence, a phenomenon not seen in the patients. The deviant findings were unexpectedly more circumscribed in the schizophrenia than in the schizotypal personality disorder (SPD) patients. Future studies should include several concurrent psychophysiological measures.