The present findings suggest that high levels of positive subclinical symptoms in participants with no history of an axis I psychotic or affective disorder are associated with significantly better performance on measures of working memory, verbal learning, and visual learning as measured by the MCCB. Moreover, although no effect of high negative symptoms was noted on MCCB performance, ancillary findings indicated that those who scored high on negative symptoms evidenced significantly better performance on a measure of estimated IQ (WRAT-3 Reading subtest). These results are at odds with several prior reports that have generally shown a negative relationship between neurocognitive functioning and severity of subclinical psychotic symptoms (Jabben et al., 2007; Laurent et al., 2001; Simons et al., 2007; van Os et al., 2005).
Our findings suggest some potential discontinuities between clinically significant psychotic symptoms and sub-syndromal manifestations of psychosis. Specifically, if subclinical psychosis represents a milder manifestation of the psychotic symptoms observed in disorders such as SZ, we might expect to see cognitive impairment in the individuals exhibiting high levels of subclinical psychotic symptoms similar to, albeit less severe than, those observed in SZ. Indeed, it CGP 41251 has generally been found that cognitive deficits consistently accompany clinically significant psychotic symptoms (Bora et al., 2010; Lewandowski et al., 2011; Simonsen et al., 2011). Contrary to this expectation, however, we found better cognitive performance in individuals with high levels of subclinical psychosis.
One possible explanation for this discrepancy is that symptom severity bears a correlational, but not causative, relation to neurocognitive capacity. Support for this idea draws from a series of complementary findings that suggest higher cognitive capacities act as a resilience factor against clinically significant psychosis (Green, 1996; Green, Kern and Heaton, 2004; Morrison et al., 2004). First, patients with higher a priori cognitive capacities tend to have better functional outcomes than patients with lower cognitive capacities (Green, 1996; Green, Kern and Heaton, 2004). Moreover, the risk of transitioning from a prodromal state to a psychotic disorder is significantly associated with impaired neurocognitive function (Keefe et al., 2006). Thus, when considering the population of individuals with high levels of subclinical psychosis, those with low a priori cognitive capacities would be expected to transition to clinically significant psychosis at a higher rate while those with higher cognitive capacities would be expected to pool in comparatively larger numbers in the subclinical domain because their high cognitive capacities protect them from transitioning. If this is the mechanism at work, then the results of the present study could be attributed to an inherent sampling bias. This conclusion would also suggest that the cognitive deficits observed in psychotic disorders such as SZ may be independent from the positive and negative symptoms characteristic of the illness. This is consistent with several lines of research suggesting that psychotic and cognitive symptoms may be separable and perhaps independent characteristics of SZ (see Harvey et al., 2006 for a review).
It is also possible, however, that there is a direct causative link between subclinical psychosis and increased cognitive function. Several studies seeking to elucidate why psychosis continues to persist despite the substantial decrements in reproductive fitness associated with it, have proposed that genetic variants associated with subclinical psychosis may be beneficial in some way. Several studies have suggested that some of the risk variants may be associated with heightened creativity or other intellectual abilities (Batey and Furnham, 2008; Burch et al., 2006; Claridge and Blakey, 2009; Green and Williams, 1999; Karlsson, 1970; Keefe and Magaro, 1980; Kéri, 2009;Miller and Tal, 2007). For example, Karlsson (1970) found that patient relatives, but not the patients themselves, had a significantly higher probability of being persons of eminence than people in the general population, and Green and Williams (1999) reported that individuals with higher scores on a test of schizotypy produced the most creative responses on a divergent thinking battery.