Event-related potential components N1, P2 and P3 to rare and frequent stimuli in intellectually impaired neurological patients.

Event-related potentials (ERPs) and attention performance data were collected in an auditory odd-ball paradigm from 24 intellectually impaired neurological patients, and compared with normal controls (n = 19). For the ERP components N1, P2 and P3, reference-independent measures (latency, global field power, current density at Cz, location of extreme potential, centroid location) were determined for the target stimulus and for the preceding and the following two "frequent" stimuli. In 8 of the 45 measures obtained, patients and controls differed significantly. To target stimuli, patients had shorter N1 latency and smaller current density, more posterior P2 location and longer P3 latency; to immediately following "frequent" stimuli, longer P2 latency; and to preceding and both following "frequent" stimuli, smaller P2 current density. Attention performance was significantly worse for the 15 patients who scored on at least one of the eight ERP measures above normal range than for the other 9 patients. Decreased N1 latency to targets is viewed as failure to activate normal attentional capacity; changed P2 location suggests activation of deviant neuronal populations in response to targets; and increased post-target P2 latency suggests abnormal persistence of induced state change.