The N2 event-related potential reflects attention deficit in schizophrenia

Schizophrenia involves deficits in detection and filtering of irrelevant stimuli. The N2 event-related potential (ERP), most likely reflecting classification of deviant stimuli, remains largely unstudied in this group. Recently, we reported that N2 amplitude correlated highly with reduced neocortical and medial temporal lobe volumes in schizophrenics. However, little is known about the functional properties of N2 in schizophrenics. To that end, the latency and amplitude of N2 were assessed in schizophrenic and control subjects to differently pitched tones. Subjects pressed a button in response to low probability (p = .15) target tones interspersed among high probability standard tones. Tones were either NEAR (1.4 kHz standard, 1.5 kHz target) or FAR (1 kHz standard, 1.5 kHz target) in pitch. N2 was measured from difference waveforms, subtracting ERPs on a simple reaction time task (target p = 1.0) from those of the detection task. Schizophrenics performed the detection task nearly as well as controls in the FAR condition, and more poorly in the NEAR condition. Schizophrenics displayed virtually no N2 amplitudes in either condition. The results are interpreted as electrophysiological signs of disturbance in stimulus classification and attention processes in schizophrenia directly related to pathology of N2 neural generators, independent of sensory or detectability problems.