Background: Alterations of the auditory evoked P300 potential are among the most reliable biological markers of schizophrenia. The aim of this study was to assess the amplitude, latency, and topography of the P300 in individuals at clinical high risk for psychosis.
Methods: P300 event-related potentials were acquired with an auditory oddball paradigm from 100 patients putatively in an early initial prodromal state (EIPS) for psychosis or in a late initial prodromal state (LIPS), according to the criteria of the German Research Network on Schizophrenia, and from 40 healthy controls comparable with respect to age, gender, and estimated verbal IQ.
Results: In the LIPS group, P300 amplitude was significantly smaller at midline and left hemispheric electrodes in comparison with controls. In the EIPS group, P300 amplitude was significantly reduced at a left temporoparietal site (TP7). A family history of schizophrenia was associated with smaller posterior P300 amplitudes in high-risk individuals. Midline P300 amplitudes were smaller in LIPS who had experienced already brief limited intermittent psychotic symptoms.
Conclusion: Smaller P300 amplitudes are present prior to a putative onset of psychosis in high-risk individuals. Selective left temporoparietal amplitude deficits may indicate a trait-like abnormality whereas deficits at sagittal midline electrodes may be partly determined by the changes that underlie the appearance of psychotic symptoms. P300 amplitude may be associated with left superior temporal lobe maturation abnormalities followed by further functional impairments later in life. Our follow-up study will reveal whether P300 amplitude alterations predict psychosis and help to targeting early intervention.