Differences between paranoid and nonparanoid schizophrenic patients on the somatosensory P300 event-related potential

Event-related potentials were recorded from schizophrenic patients (n = 30) and healthy controls (n = 30) using a somatosensory-reaction-time version of the oddball paradigm, by stimulating the right and the left median nerve. Latency, amplitude, duration and area of the P300 were measured. The patient group was subdivided into a paranoid (n = 16) and a nonparanoid (n = 14) subgroup and each was compared to controls. After stimulation of the right median nerve the nonparanoid group had a significantly prolonged P300 latency and a normal amplitude. The paranoid subgroup had a trend toward reduction of the P300 amplitude; its P300 latency was normal. After stimulation of the left median nerve, a prolongation of the P300 latency was observed in the paranoid subgroup. This subgroup had also a reduced P300 amplitude, while the nonparanoid patients had both values comparable to those of the controls. Duration and area were not significantly different between the two subgroups of patients and controls. Paranoid and nonparanoid patients showed a different behavior on reaction time parameters. No relationship was observed between P300 parameters and clinical ratings, neuroleptic dose and demographic data. The P300 parameters did not correlate with the reaction time measures. These results are discussed in terms of a disturbance of CNS inhibitory mechanisms in cognitive processes of paranoid schizophrenic patients and could be a further indication that different subtypes of schizophrenia may have different biological substrates.