The impact of parent socio-economic status on executive functioning and cortical morphology in individuals with schizophrenia and healthy controls.

Growing up in an impoverished socioeconomic environment is associated with a number of environmental, health, and developmental disparities in children that persist well into adulthood. Though genetic factors clearly affect brain development, there is also substantial evidence for early sociocultural influences on the risk of developing both schizophrenia (van Os, 2010) and relatively lower cognitive functioning (Nisbett et al., 2012). Socioeconomic status (SES) in particular has been frequently examined for its impact on cognitive skills (Hanscombe et al., 2012). The effects of low socioeconomic status (SES) are probably greater in some cognitive domains than others. Executive or “frontal lobe” skills may be especially affected (Hackman et al., 2010). The neurological substrate for these skills includes diverse prefrontal regions that frequently show morphological abnormalities in schizophrenia (Eisenberg and Berman, 2010). The adverse effects of low SES may also be greater for some individuals than others, including individuals vulnerable to schizophrenia. We have suggested that a cardinal feature of schizophrenia is reduced canalization, i.e., difficulty in getting development back on a normal trajectory following significant perturbations (Yeo et al., 1999, Yeo et al., 2007). Consistent with this perspective, individuals at risk for schizophrenia have been found to be more influenced by such environmental issues as obstetric complications (McNeil et al., 2000) and marijuana (Habets et al., 2011) and alcohol use (Welch et al., 2011). The current study thus sought to test the hypothesis that low parental SES (pSES) has a greater adverse impact on executive skills and cortical morphology in individuals with schizophrenia than healthy controls. Impaired executive functioning is one of the most commonly noted deficits associated with schizophrenia (Eisenberg and Berman, 2010). Several different types of correlated skills are typically subsumed under “executive” or “frontal lobe” skills, including planning, monitoring, working memory, fluency, cognitive control, and self-regulation/impulse control. Of course, other cognitive deficits are common in schizophrenia and recent large-scale factor analytic studies demonstrate the existence of a generalized cognitive deficit, in addition to deficits in secondary factors (Dickinson et al., 2011). Executive deficits may also be central to the endophenotype of schizophrenia (Gottesman and Gould, 2003) for several reasons. Executive ability is heritable (Friedman et al., 2008) and non-schizophrenic relatives of individuals with schizophrenia have relatively impaired executive performance (Snitz et al., 2006) and reduced prefrontal gray matter volumes (Goghari et al., 2010). Moreover, a study with first episode patients showed that severe impairment of executive functioning was present at the beginning of the disease (Hutton et al., 1998). It is also important to note that executive deficits have important real-world consequences for individuals with schizophrenia. Lower executive skills predict reduced insight (Chan et al., 2012), reduced daily living skills (Puig et al., 2012), and reduced levels of remission (Hofer et al., 2011). Despite these prominent correlates, caution must be exercised in asserting the primary cognitive importance of executive deficits, as general intellectual ability (“g”) correlates substantially with most measures of executive skill. The manner in which low parental SES might impact executive skill and its anatomical substrates is poorly understood. A recent meta-analysis of functional neuroimaging studies concluded that similar brain networks were activated in both individuals with schizophrenia and controls during performance of executive tasks, e.g., dorsolateral, ventrolateral, and midline prefrontal regions, as well as the anterior cingulate gyrus (Minzenberg et al., 2009). We are not aware of any studies that have specifically examined the impact of pSES on these brain structures, though studies of related social factors have begun to emerge. Healthy children of healthy parents with low income were found to have reduced hippocampal volume in a recent voxel-based morphometry (VBM) study (Hanson et al., 2011), but prefrontal regions were not examined. Other studies focusing on adverse childhood experiences have found that healthy adults with substantial early life stress had reduced anterior cingulate and caudate volumes (Cohen et al., 2006), while a related study noted that childhood emotional maltreatment was associated with reduced medial prefrontal cortex volumes (van Harmelen et al., 2010). An important question is whether the regions identified in these studies are affected by low pSES in individuals with schizophrenia. The first goal of the current study was to investigate the association of parental SES with executive function in both healthy controls and patients with schizophrenia. Results indicated a greater impact of pSES in patients than controls. To follow up this finding, the second major goal of the current study was to evaluate the impact of pSES on cortical gray matter in both groups using VBM.