Background

A 'continuum of psychosis' refers to the concept that psychotic-like experiences occur to certain extents in the healthy population and to more severe extents in individuals with psychotic disorders. If this concept is valid, neurophysiological abnormalities exhibited by patients with schizophrenia should also be present, to some degree, in non-clinical individuals who score highly on the personality dimension of schizotypy. Patients with schizophrenia have consistently been shown to exhibit electrophysiological suppression abnormalities to self-generated speech. The present study aimed to investigate whether these electrophysiological suppression abnormalities were also present in non-clinical individuals who scored highly on schizotypy.

Methods

Thirty-seven non-clinical individuals scoring High (above median) and 37 individuals scoring Low (below median) on the Schizotypal Personality Questionnaire (SPQ; a commonly used schizotypy scale) underwent electroencephalographic (EEG) recording. The amplitude of the N1 component of the auditory-evoked potential was measured while participants (a) vocalized simple syllables (Talk condition), (b) passively listened to a recording of these vocalizations (Listen condition) and (c) listened to a recording of the vocalizations while simultaneously watching a video depicting the sound-wave of the forthcoming vocalizations, allowing them to be temporally predicted (Cued Listen condition).

Results

The Low Schizotypy group exhibited significantly reduced N1-amplitude in the Talk condition relative to both the Listen and Cued Listen conditions; that is, they exhibited significant N1-suppression. The High Schizotypy group exhibited significantly lower levels of N1-suppression compared to the Low Schizotypy group. Furthermore, while the Cued Listen condition induced significantly lower N1-amplitudes compared to the Listen condition in the Low Schizotypy group, this was not the case for the High Schizotypy group.

Conclusions

The results suggest that non-clinical, highly schizotypal individuals exhibit subnormal levels of N1-suppression to self-generated speech, similar to the N1-suppression abnormalities which have previously been reported in patients with schizophrenia. This finding provides empirical support for the existence of a neurophysiological 'continuum of psychosis'.