Bases for irrelevant information processing in schizophrenia: Room for manoeuvre

Kamin blocking is not disrupted by amphetamine in human subjects

The effect of oral amphetamine administration on the Kamin-blocking effect in healthy volunteer subjects was investigated. Against predictions, Kamin blocking was not disrupted by either a high or low oral dose of D-amphetamine under conditions which have, in previous studies, led to disruption of a related learning phenomenon (latent inhibition). This lack of effect of amphetamine administration upon Kamin blocking weakens hypotheses that this cognitive process is mediated by the same changes in dopaminergic activity which affect latent inhibition. Currently, the only data which show strong comparative associations between Kamin blocking and latent inhibition are when they are applied to schizophrenic populations. These results may suggest that Kamin blocking and latent inhibition may be measuring different aspects of schizophrenic cognitive dysfunction.

Mismatch negativity--a unique measure of sensory processing in audition

Physically deviant auditory stimuli occurring among frequent ("standard") stimuli (e.g., tones or phonetic stimuli) elicit the mismatch negativity (MMN) of the auditory event-related potential (ERP). The MMN is presumably generated by a mismatch process between the sensory input from a deviant stimulus and a neural sensory-memory trace representing the physical features of the standard stimulus. This process, as well as sensory analysis of auditory input and its encoding into the memory trace, appear to be automatic since the MMN is elicited even by changes in unattended auditory stimuli. Therefore the MMN indirectly provides a unique, objective measure of the central representation of a sound. This opens new possibilities for basic research as well as clinical and other applications.

Memory template comparison processes in anhedonia and dysthymia

Anhedonic subjects, potentially at risk for psychopathology because of a deficient ability to experience pleasure, have demonstrated a large N200 component in the event-related brain potential (ERP). The present experiment attempted to determine the psychological significance of this finding in light of Näätänen's (1990) distinction between N2a and N2b subcomponents. Anhedonics were contrasted with controls and dysthymics, an at-risk group reporting depression. Across groups, N2a was larger when a tone mismatched a longer run of preceding identical tones. Thus, an involuntary mismatch process appears to be intact in both at-risk groups. However, the three groups produced distinct N2bs as a function of stimulus sequence. The N2b finding for anhedonics is consistent with Knight's (1984, 1992) model of early stimulus processing deficits in schizophrenia.