P300 IN SCHIZOPHRENIA - INTERACTIONS BETWEEN AMPLITUDES AND TOPOGRAPHY

Low P300 amplitudes and topographical asymmetries have been reported i n schizophrenic patients, but reference-independent amplitude assessme nt failed to replicate reduced amplitudes. P300 amplitude is conventia lly assessed at midline electrodes (Pt), and asymmetric topography as reported in schizophrenics, may confound this measurement. We investig ated the possible interaction between P300 topography and assessments of amplitudes. In 41 clinically stable schizophrenics and 31 normal co ntrols, the general finding of reduced amplitudes at the Pt-electrode and topographical asymmetries in the patient group were replicated. In both groups, asymmetries of the P300 field (lateralized peaks) reduce d the standard amplitude assessment at the midline parietal electrode, but did not affect the reference-independent, global amplitude assess ment. This shows that asymmetry per se does not imply reduced field st rength. In addition, in schizophrenics, but not in controls, there was a significant effect of the direction of asymmetry on both amplitude measures, amplitudes being lower with increasing shift of the P300 pea k to the right side. Considering also the slightly left-lateralized pe aks in the normal controls, this suggests that only right-lateralized P300 peaks express functional deficits in schizophrenics, whereas left -lateralized peaks fall within the physiological variability of the P3 00 field The reference-independent amplitude assessment is proposed fo r unambiguous amplitude assessment in order to better define the clini cal, psychological and physiopathological meaning of the P300 alterati ons in schizophrenics.