"Generalized Cognitive Deficit" in Schizophrenia: Overused or Underappreciated?

Abstract

Green, Horan, and Sugar provide a new look at the generalized cognitive deficit problem in schizophrenia and argue persuasively that the criticism is not appropriate in a variety of circumstances. More significantly, noting a decrease in mentions of the general deficit problem in published literature in recent years, along with mounting evidence of areas of relatively normal cognitive performance in people with this illness, Green et al suggest that the generalized deficit may come to be of lesser importance in contemporary schizophrenia research and that, increasingly, it is yielding ground to developing behavioral and neuroimaging methodologies that permit ever more precise parsing of cognitive operations and neural systems. We suspect the reason that Green and colleagues had difficulty retrieving recent papers addressing the generalized deficit is that the evidence documenting it has simply become so overwhelming. That is, the 40-year search for focal, specific deficits, bounded by evidence of normal performance on other related measures, has been largely disappointing. Enormous effort was expended in the late 20th century trying to substantiate claims for certain differential cognitive deficits in schizophrenia, and ideas took hold then that still hold sway (“deficits in executive functions and episodic memory are particularly pronounced in this illness”). In the context of this effort, the general deficit was considered a nuisance that obscured the ability to identify critical deficits that might have provided important clues to understanding the psychological and neural mechanisms implicated in the illness. In the clinic and the assessment lab, however, what was always most striking was the overall cognitive impairment in people with schizophrenia relative to control groups rather than any particular peaks or valleys in the performance profile. Study after study showed a reduced performance in those with the illness, generally in the vicinity of 1.0 SD, across a wide range of neuropsychological measures. Meta-analyses of neuropsychological data from thousands establish unambiguously that this is the rule in schizophrenia—at least for these sorts of measures. Thus, the lack of recent interest in the general deficit may reflect a realistic appraisal of the state of the art; clinical neuropsychological methods that have dominated the research literature over the past 25 years offer little evidence of differential deficits. To us, it is deeply puzzling that this has not become a major focus of schizophrenia research and experimental psychopathology—it is the elephant in the room for cognitive studies. Green et al cite a number of recent papers that report areas of intact cognitive function in schizophrenia—papers that call into question the generality of the generalized deficit. Although one of us (JG) has contributed multiple experimental papers to this literature, in regard to the generalized deficit debate, we both consider these findings with caution. As noted by Green et al, these findings often emerge from highly constrained experiments designed to isolate specific component operations, and the extent to which patient performance is fully “normal” is not always straightforward. For example, in the Posner spatial cuing paradigm, there is robust evidence that patients are able to use cues to facilitate reaction time (normal effect of selective attention), but patients are nearly invariably substantially slower overall than controls.1 In our series of working memory experiments demonstrating intact operation of selective attention in guiding the encoding of relevant items and suppression Schizophrenia Bulletin Advance Access published December 4, 2012