Deficits in auditory and visual context-dependent processing in schizophrenia - Defining the pattern

Background: Brain mechanisms underlying deficits in precision of transient memory storage in schizophrenia were investigated using a combined behavior al and eventrelated potential approach. Performance was measured simultaneo usly in 2 tasks: an AX-type visual continuous performance test (AX-CPT), wh ich required subjects to press a button whenever they saw a letter A follow ed by a letter X, and a mismatch negativity paradigm. The AX-CPT is designe d to assess prefrontal function, whereas mismatch negativity assesses funct ioning of the auditory sensory memory system. Methods: Subjects were 17 patients with chronic schizophrenia, 13 with rece nt-onset schizophrenia, and 20 normal comparison subjects. Potentials were recorded from 36 scalp locations in response to cue stimuli in the CPT and to duration- and pitch-deviant stimuli in the mismatch negativity paradigm. Behavioral measures including responses to incorrect cue-target sequences that should have been ignored ("false alarms") were analyzed as a function of cue-target interval. Results: Chronic and recent-onset schizophrenic patients showed significant ly decreased mismatch negativity amplitude but normal latency and topograph y. In the CPT, patients showed significantly higher rates of false alarms f ollowing incorrect cues ("BX" errors) and decreased rates of correct detect ions. Impaired performance correlated with decreased frontocentral event-re lated potential activation to incorrect cues that was manifest within sever al hundred milliseconds of cue presentation. All groups performed worse wit h increasing cue-target intervals. Patients were no more affected by increa sed cue-target interval than were controls. Conclusions: Schizophrenic patients are significantly impaired in their abi lity to form and utilize transient memory traces to guide behavior. These d eficits are associated with failures of cortical activation occurring withi n several hundred milliseconds of stimulus presentation. A similar pattern of deficit is observed across sensory and cognitive systems.