• Working Memory and Executive Functioning Impairment as Endophenotypes of Schizophrenia Spectrum Disorders

      Iati, Carina A. (2012-10-19)
      Evidence indicates that impairments in working memory and executive functioning exist in individuals who have decompensated into schizophrenia, as well as their genetic relatives. Few studies, however, have examined whether these impairments function as premorbid indicators of vulnerability to schizophrenia-related disorders in the absence of genetic relatedness for risk determination. According to Meehl’s (1962, 1990) model of schizotypy individuals vulnerable to schizophrenia-related disorders evidence subtle symptoms of vulnerability, referred to as endophenotypes, regardless of whether eventual decompensation occurs. The present study represents a cross-sectional portion of a larger longitudinal study, and investigates whether individuals who demonstrate an elevated risk for future development of schizophrenia spectrum disorders also demonstrate these impairments compared to a normal-risk group in a sample of college students. Risk status was determined by participants’ Wisconsin Schizotypy Scale (WSS) scores. Working memory subtests from the Wechsler Adult Intelligence Scale–IV (WAIS-IV) and Wechsler Memory Scale-IV (WMS-IV) were compared across individuals determined to be at high risk (psychometric schizotypes; PS) and a matched comparison (MC) sample. Executive functioning, as measured by the Wisconsin Card Sorting Task (WCST), was also compared across these groups. It was hypothesized that schizotypes would exhibit impairment in both of these abilities. Additionally, it was hypothesized that a linear relationship would exist between level of deviancy demonstrated on the WSS and the level of impairment demonstrated on executive functioning and working memory tasks. Results failed to support the hypothesis that aggregate working memory or executive functioning deficits were significantly related to schizotypy. However, performance on the WMS-IV Visual Working Memory Index (VWMI) and the Spatial Addition subtest of this measure indicated impaired performance by PS participants compared to the MC group. Similarly, this investigation failed to find support for a linear relationship between level of impairment and deviance on PerAb and MagId WSS subscales. However, scores on the SocAnh scale did demonstrate an inverse relationship with performance on the VWMI. Further analyses which grouped the PS participants by symptom presentation, revealed that individuals exhibiting a negative symptom presentation, as indicated by deviant scores on the SocAnh scale, demonstrated impairment in visual working memory in comparison to both the MC group and their Per-Mag counterparts who exhibited more positive symptoms. This result is in agreement previous investigations that have specified visual working memory impairment as being related to negative symptom presentation (Cameron, 2002; Park et al., 2003). These results may be influenced by characteristics of the present sample, as the majority of individuals who reported symptoms did so on negative symptom dimensions, with only 6 individuals reporting positive symptomology. Negative symptom dimensions have been proposed to be related to working memory impairment (Gooding & Tallent, 2002), whereas positive symptoms have been proposed to be related to impairment in executive functioning (Donohoe et al., 2006; Lenzenweger & Korfine, 1994). The relative lack of individuals with positive symptom presentation in the current sample likely led to the lack of any notable results with regard to executive functioning. Results of this investigation aid our understanding of the course of schizophrenia spectrum disorders, and join the broad body of literature investigating candidate endophenotypes. Future directions for related research include continued investigation into the differences between verbal and visual working memory as related to schizophrenia spectrum disorders, investigation of the present candidate endophenotypes alongside other proposed markers of liability, and longitudinal investigation to determine whether individuals possessing candidate endophenotypes exhibit a greater number of schizophrenia spectrum symptoms.