Linguistic Determinants of Formal Thought Disorder in First Episode Psychosis

Background: Disturbances in the expression of thought is a core feature of schizophrenia but assessment of disordered thinking is challenging, relying on clinical intuition which may contribute to the paucity of mechanistic understanding of disorganization seen in early stages of psychosis. We studied the use of linguistic connectives in relation to clinically quantified dimensions of thought disorder using automated speech analysis in untreated, first episode psychosis (FEPs) and healthy controls (HCs)Methods: Data were collected from 39 treatment-naïve, actively psychotic first episode patients (FEPs) recruited on first contact and 23 group matched healthy controls. Three one-minute speech samples were induced in response to photographs from the Thematic Apperception Test and speech was analyzed using COH-METRIX software. Five connectives variables from the Coh-Metrix software were reduced using principle component analysis, resulting in two linguistic connectives factors. Thought disorder was assessed using the Thought Language Index (TLI) and the PANSS-8. Results: linguistic connective factors predicted disorganized thought, but not impoverishment suggesting aberrant use of connectives is specific to positive thought disorder. Factor 2 (increased temporal, reduced logical connectives), showed statistically significant main effects (F[2,56]=5.58, p=0.006) on ANOVA among HCs, low- and high-disorganization FEPs. Post-hoc differences were noted between High- and Low- disorganization FEPs (p=0.004). Factor 2 was not correlated with measures of disease severity or cognition suggesting connective use is a specific index of disorganized thinking rather than overall illness status. Conclusions: Disorganization in psychosis, assessed on the basis of clinical judgement, is likely linked to the excessive or inappropriate use of linguistic connectives leading to an intuitive sense of incoherence to the observer. In the early stages of untreated psychosis, thought disorder may be quantifiable more reliably using automated syntax analysis.