Evoked potential measures of language processing in schizophrenia

Abstract

The Continuous Performance Test (CPT) has been used extensively in studies concerned with attentional deficits in schizophrenia, however, the cognitive subprocesses underlying CPT performance are poorly understood. Startle eyeblink modification (gEM) is a psychophysiological measure which has the potential to separately evaluate discrete stages of information processing. When a nonstartling prepulse precedes a startleeliciting stimulus by a short interval (250 ms or less), the startle reflex is reliably inhibited. This prepuise inhibition is thought to reflect the early stages of information processing associated with sensory gating. When the interval is longer (1000 ms or greater), gEM is thought to reflect later stages of information processing. This study employed the gEM technique to index early and later stages of attentional processing during a visual memory-load version of the CPT with auditory (tone) distractors. Relatively remitted schizophrenic outpatients (n-20) and matched normal controls (n-18) viewed a series of single digits some of which served as prepulses for a startle.eliciting noise burst. Subjects were instructed to press a button after the digit 7 of each 3-7 sequence. The noise burst was presented either 120 or 1200 ms following the onset of preselected Target (i.e., Y'), Nontarget (non-3, non-7 digits), and Target plus Distractor (Y' and simultaneous tone distractor) prepuises, as well as in the absence of a prepulse (baseline). Primary results indicate that for control subjects the Target prepulse produced significantly greater inhibition than the Nontarget prepulse at the 120 ms lead-interval, suggesting early stimulus discrimination and selective attention. Also, significant but nondifferential prepulse inhibition was observed following the Target prepulse and the Target plus Distraetor prepulse, suggesting that the controls effectively ignot~l the distractor. In contrast, the patients failed to show differential prepulse inhibition to the Target and Nontarget prepulses. However, they did show attentional modulation of gEM as they exhibited significantly greater prepulse inhibition following the Target plus Distractor prepulse. These findings suggest that CPT deficits in schizophrenia are associated with inefficient early controlled attentional processes. Together with animal models of prepulse inhibition, gEM offers a unique way to delineate the neural basis of information processing deficits in schizophrenia.