Neurological soft signs and psychometrically identified schizotypy in a sample of young conscripts
Introduction
Neurological ‘soft’ signs (NSS) are subtle neurological abnormalities pertinent to integrative sensory function, motor coordination and motor sequencing that are not attributed to specific brain areas (Buchanan and Heinrichs, 1989). It has been suggested that NSS might represent nonspecific cerebral dysfunctions in schizophrenia; Andreasen et al. (1998) hypothesized a disruption in a cortico-cerebellar-thalamic-cortical circuit leading to impaired sequencing and coordination of mental processes, manifested in symptoms associated with schizophrenia (cognitive dysmetria).
Compared with healthy controls, individuals with schizophrenia exhibit more NSS (Heinrichs and Buchanan, 1988, Arango et al., 1999, Dazzan and Murray, 2002, Keshavan et al., 2003, Bombin et al., 2005 Picchioni and Dazzan, 2009, Whitty et al., 2009, Chan et al., 2010a, Chan et al., 2010b). NSS have been observed in first episode schizophrenic patients (Dazzan and Murray, 2002), and in antipsychotic-naïve patients (Gupta et al., 1995). NSS may also occur before the onset of schizophrenia, in children (Walker et al., 1994), and in subjects at high risk of developing schizophrenia (Griffiths et al., 1998). Furthermore, elevated rates of NSS in healthy biological relatives of schizophrenic patients have been reported (Neelam et al., 2011), with NSS scores intermediate between those of patients and healthy controls (Egan et al., 2001, Yazici et al., 2002, Compton et al., 2007). It has been proposed that the presence of neurological abnormalities in groups at high risk for schizophrenia might represent a genetic vulnerability marker (Bachmann et al., 2005). A recent suggestion is that NSS might constitute a potential endophenotype for schizophrenia (Chan and Gottesman, 2008).
Regarding psychopathology, research findings suggest that NSS in schizophrenia are related to severe negative symptoms (Schröder et al., 1992, Malla et al., 1997, Arango et al., 2000, Dazzan and Murray, 2002, Yazici et al., 2002, Bombin et al., 2005, Ruiz-Veguilla et al., 2008, Chan et al., 2010a, Chan et al., 2010b) and disorganized symptoms (Schröder et al., 1996, Arango et al., 2000, Compton et al., 2007, Mechri et al., 2009). In contrast, positive symptoms seem unrelated to NSS (Bombin et al., 2005).
There is a growing interest in the connection between NSS and schizophrenia spectrum disorders like schizotypal personality disorder. Healthy individuals with schizotypy have been found to demonstrate increased numbers of NSS (Barrantes-Vidal et al., 2003, Barkus et al., 2006, Bollini et al., 2007, Keshavan et al., 2008, Kaczorowski et al., 2009, Prasad et al., 2009, Chan et al., 2010b, Mechri et al., 2010). Table 1 lists studies correlating schizotypy and NSS. It should be noted that the first, second, third, seventh and ninth studies (Obiols et al., 1999, Barrantes-Vidal et al., 2003, Barkus et al., 2006, Kaczorowski et al., 2009, Chan et al., 2010b) involved only healthy participants, while the fourth, fifth, sixth, and eighth studies (Bollini et al., 2007, Keshavan et al., 2008, Prasad et al., 2009, Mechri et al., 2010) also involved relatives of patients with schizophrenia or subjects at high risk for schizophrenia.
We sought to investigate potential associations between NSS and self-reported schizotypal traits in a sample of young healthy male conscripts (n 169) from the Athens Study of Psychosis Proneness and Incidence of Schizophrenia (ASPIS). Firstly, we sought to investigate potential correlations between NSS and schizotypy scores on the Schizotypal Personality Questionnaire (SPQ) in the entire sample. Secondly, the outcome was highlighted by comparing the NSS scores of conscripts with high schizotypy scores versus conscripts with average ones. Thirdly, regression models were implemented to validate the resulting associations by adjusting for possible confounding effects.
Section snippets
Setting and sample
A subgroup of 169 male subjects from the Athens Study of Psychosis Proneness and Incidence of Schizophrenia (ASPIS) were assessed for NSS at T2, 2 years after the first assessment for schizotypal features (T1), based on the following criteria derived from SPQ scores at T1: a) high scorers (who scored above the 90th percentile, 47%) and b) average scorers (who scored close to the mean value, 53%). Findings in the study by Raine (1991) indicated that 55% of those subjects who score in the top 10%
Descriptive indices
Table 3 presents the descriptive indices of Raven's Progressive Matrices (RPM), NSS, and SPQ scores. The four-factor solution (Stefanis et al., 2004) is presented. However, note that in the four-factor solution the Interpersonal/negative and the disorganized factors are identical with the three-factor solution; that is, they consist of the same items (Raine, 1991). SPQ scores were significantly lower at T2 (p < 0.001). The reduction varied from 42% to 62% at the SPQ subscale level.
Correlations of SPQ scores with NSS
At both time
Discussion
The results of the present study can be summarized as follows:
- a)
First, NSS were more prominent in healthy subjects with high negative schizotypy at both time points (T1 and T2), demonstrating temporal stability of this association. Specifically, the Sequencing of Complex Motor Acts (SCMA) subscale, and the total NSS scores were significantly correlated (p < 0.05) with the interpersonal factor at both time points (T1 and T2).
- b)
Second, NSS were more prominent in conscripts with high schizotypy; scores
Acknowledgements
This work was supported by the Grant EKBAN 97 to C.N.S. from the General Secretariat of Research and Technology of the Greek Ministry of Development. Intrasoft provided the technical support for this project.
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