پیش بینی عملکرد آزمون تلاش های عصب در اسکیزوفرنی

There is some evidence that insufficient effort may be common in schizophrenia, posing significant threats to the validity of neuropsychological test results. Low effort may account for a significant proportion of variance in neuropsychological test scores and the generalized cognitive deficit that characterizes the disorder. The current study evaluated clinical predictors of insufficient effort in schizophrenia using an embedded effort measure, the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) Effort Index (EI). Participants were 330 patients meeting DSM-IV-TR criteria for schizophrenia, schizoaffective disorder, or another psychotic disorder who received a battery of neuropsychological tests, including: Wechsler Test of Adult Reading (WTAR), Wechsler Abbreviated Scale of Intelligence (WASI), and RBANS. Clinical assessments designed to measure functional outcome and symptoms were also obtained. Results indicated that 9.4% of patients failed the EI. Patients who failed had lower full-scale, verbal, and performance IQ, as well as poorer performance on RBANS domains not included in the EI (immediate memory, language, and visuospatial/construction). Patients who failed the EI also displayed poorer community-based vocational outcome, greater likelihood of having “deficit schizophrenia” (i.e., primary and enduring negative symptoms), and increased severity of positive symptoms. Regression analyses revealed that insufficient effort was most significantly predicted by a combination of low IQ, negative symptoms, and positive symptoms. Findings suggest that although insufficient effort may be relatively uncommon in schizophrenia, it is associated with important clinical outcomes. The RBANS EI may be a useful tool in evaluating insufficient effort in schizophrenia.

Neuropsychological impairment is common in schizophrenia, and has long been considered a core feature of the illness (Kraepelin, 1919). Meta-analyses indicate that individuals with schizophrenia display neurocognitive impairments approximately one standard deviation below the mean for healthy controls (Fioravanti et al., 2005 and Dickinson et al., 2007). Despite such pervasive cognitive impairments, there is no distinct pattern of differential deficits that characterizes most individuals with schizophrenia (Reichenberg and Harvey, 2007). Rather, schizophrenia patients display neurocognitive impairments of similar magnitude across most cognitive domains, suggesting a generalized neurocognitive deficit (Dickinson et al., 2004, Dickinson, 2008 and Dickinson et al., 2008). Several theories have been proposed to account for this generalized neurocognitive deficit, including central nervous system (e.g., gray and white-matter abnormalities, impaired integration of signals across neural networks, and cellular-level neuropathology) and “general systems” (e.g., inflammatory, metabolic, and oxidative stress processes) abnormalities that can negatively impact cognition (Dickinson and Harvey, 2009). However, it is also possible that psychological factors contribute substantially to the neurocognitive impairments observed in schizophrenia. One possibility is that problems with motivation result in inadequate effort on measures of neurocognition, particularly on tasks that are more cognitively demanding. To date, relatively few studies have examined insufficient effort during neuropsychological testing in schizophrenia and whether such abnormalities are associated with motivational problems. Those studies that have been conducted have produced inconsistent results, with the majority indicating that a small proportion of individuals with schizophrenia (~ 20%) perform below clinically established cut-off scores for valid effort (Back et al., 1996, Egeland et al., 2003, Arnold et al., 2005, Duncan, 2005, Gierok et al., 2005, Avery et al., 2009, Pivovarova et al., 2009, Schroeder and Marshall, 2011, Moore et al., 2013 and Hunt et al., 2014), and other studies indicating that up to 60–72% of the sample may fail effort testing (Gorissen et al., 2005 and Hunt et al., 2014). Despite these inconsistencies regarding rates of effort test failure, there is reliable evidence that certain clinical variables predict low effort in schizophrenia. For example, multiple studies have found that global scores on negative symptom rating scales, such as the Scale for the Assessment of Negative Symptoms (Andreasen, 1983) or the Brief Negative Symptom Scale (Kirkpatrick et al., 2011), account for a substantial proportion of variance in effort test performance (Gorissen et al., 2005, Avery et al., 2009 and Strauss et al., 2014). Several psychological variables also differentiate patients who pass and fail effort measures, including self-reported anhedonia and the perception of low cognitive resources (Avery et al., 2009 and Strauss et al., 2014). These findings suggest that negative symptoms and psychological processes associated with negative symptoms may be core to diminished effort during neuropsychological testing. However, negative symptoms are both multi-dimensional and multi-determined and it is currently unclear which aspects of negative symptoms are associated with low effort. There is consistent evidence for the multi-dimensionality of negative symptoms, such that 2 distinct negative symptom factors are commonly identified, one reflecting diminished motivation (anhedonia, avolition, asociality) and the other diminished expressivity (alogia and restricted affect) (Blanchard and, 2006, Horan et al., 2011 and Strauss et al., 2012). These two dimensions have different demographic and clinical correlates (Strauss et al., 2013), with more severe volitional pathology generally predicting worse outcomes. Given that neuropsychological impairment has been associated with the motivational dimension more strongly than the diminished expressivity dimension (Fervaha et al., 2014), one might expect effort test performance to be specifically linked to greater severity of motivational symptoms. Furthermore, it is now generally accepted that negative symptoms are multi-determined — two patients can display identical scores on negative symptom rating scales for very different reasons. This notion was highlighted in the seminal work of Carpenter et al. (1988), which demonstrated that negative symptoms can result from either primary or secondary factors. Primary negative symptoms are those that are idiopathic to the illness, whereas secondary negative symptoms result from processes such as paranoid social withdrawal, depression, disorganization, hallucinations, and suspiciousness. If low effort is indeed critically linked to true motivational problems in schizophrenia, one might expect higher rates of effort test failure in patients who meet clinical diagnostic criteria for “deficit schizophrenia”, i.e., those with primary and clinically stable negative symptoms (Carpenter et al., 1988 and Kirkpatrick et al., 2001). Patients with deficit schizophrenia typically fall 1 SD below nondeficit schizophrenia patients and 2 SD below healthy controls on standard neuropsychological tests (Buchanan et al., 1994 and Cohen et al., 2007); however, it remains to be seen whether patients meeting clinical criteria for deficit schizophrenia are more likely to fail effort tests than nondeficit patients. In the current study, we explored rates of effort test failure in a large sample of individuals with schizophrenia using an embedded effort measure that has been well-validated in clinical populations, the RBANS Effort Index (Silverberg et al., 2007). Clinical predictors of insufficient effort were examined, with an emphasis on determining whether the motivational dimension and primary negative symptoms are most predictive of effort test failure. It was hypothesized that a small percentage of individuals with schizophrenia (< 20%) would fail the RBANS Effort Index and that patients falling below the low-effort cut-off would be more likely to meet clinical criteria for deficit schizophrenia, have greater severity of motivational symptoms, and poorer community-based functional outcome.