Formal thought disorder (FTD) is manifest clinically as incoherent speech and is a central feature of schizophrenia. Thought disordered speech appears disorganized and lacks a clear theme or goal, suggesting that impairment in speech planning might be a key underlying factor. Coherent discourse also entails the continuous monitoring and editing of the verbal output, such that the intended and articulated speech correspond. The articulation of unusual or inappropriate words and the introduction of incongruous topics in thought disordered speech are thought to reflect a deficit in verbal self-monitoring in schizophrenia.
Although normal discourse involves speech that is described as continuous, as much as 50% of the total speaking time can be taken up by pauses which typically last 250–3000 mos. Psycholinguistic research indicates that pauses are heterogeneous, with different types associated with specific components of linguistic processing. Pauses that occur between clauses are particularly associated with planning the content and grammatical structure of the succeeding utterance, while pauses occurring within clauses are more linked to lexical retrieval or word selection. Pauses can alternatively be subcategorized according to whether they are filled (and associated with the articulation of “um,” “ah,” and other “fillers”) or unfilled (silent). Filled pauses often reflect the detection of potential errors before they are articulated and may thus indicate the process of verbal self-monitoring.
The aim of the present study was to use between-clause and filled pauses as markers of speech planning and monitoring, respectively, in order to study the neural correlates of these processes with functional neuroimaging. We were particularly interested in verbal planning and monitoring because impairments in these processes have been implicated in schizophrenia, especially in relation to FTD. We therefore selected patients who not only had marked evidence of FTD, but who were displaying these symptoms at the time of scanning. On the basis of data from studies of verbal planning and monitoring in other contexts, we predicted that in controls both types of pause would be associated with activation in the left inferior frontal and left superior temporal cortex. We then tested the hypothesis that between-clause pauses and filled pauses in schizophrenic patients with FTD would be associated with attenuated activation in these regions. This was based on the putative impairments in speech planning and verbal self-monitoring in patients with FTD and previous evidence linking FTD to functional and structural abnormalities in these regions in schizophrenia.

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