• event-related potential;
  • P300;
  • inter-peak latency;
  • schizophrenia;
  • Alzheimer-type dementia

Background: Both patients with schizophrenia and those with dementia show cognitive difficulties, and in many cases of schizophrenia the cognitive disturbance is progressive, as it is in dementia. Event-related potentials have revealed cognitive impairments in patients with schizophrenia and dementia, but most studies of event-related potentials in cases of psychiatric illness or dementia have focused on the single peak latency of the event-related potential components. In the present study, we investigated the cognitive function in elderly patients with schizophrenia and Alzheimer-type dementia (AID) using auditory event-related potentials (P300).

Methods: P300 was recorded using the tone discrimination task and peak latencies for N1, P2, N2 and P3 at the Pz electrode site were measured. In addition to analyzing peak latencies of P300, we also analyzed inter-peak latencies (IPL; N1-P2, P2-N2, and N2-P3). Twenty-two elderly residual-type schizophrenics and 36 patients with AID were compared with 39 age-matched healthy volunteers.

Results: The mean latencies of P3 and mean IPL of P2-N2 in elderly schizophrenic patients were longer than those of the controls. In ATD the mean latencies of N2 and P3 and the mean IPL of P2-N2 were longer than those of the controls. When the mean latencies of ATD patients were compared with those in patients with schizophrenia, P2, N2, and P3 latencies and N1-P2 and P2-N2 IPL were longer.

Conclusion: These findings suggest that a similar impairment of the cognitive process is found in elderly patients with schizophrenia and those with ATD and that the degree of the impairment of patients with ATD is more severe than that of elderly patients with schizophrenia.