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Thought disorders are dysfunctions of thought which tend to manifest in language. This symptom tends to present itself in one or more of the following forms: language derailment, poverty of speech, strained speech, tangential association, illogical language patterns, and/or word substitutions.
Thought disorders tend to be split into positive and negative subtypes with those aspects which inhibit speech (poverty of speech, strained speech, language derailment) being classed as negative and the aspects which result in altered speech (tangential association, illogical patterns, word substitutions) classed as positive.
Research by Dwyer et al. (2014a) suggests that individuals who experience thought disorders have difficulty establishing context for language, and furthermore have difficulty using context to differentiate between emotionally negative and neutral sentences even when presented with these sentences repeatedly. Further research by Dwyer et al (2014b) indicated that the failure of some aspects of higher-order semantic processing can result in word substitutions and misattribution of context to contextless sentences. Showing that these symptoms may have a single related cause, and are the result of higher cognitive dysfunction and not the dysfunction of separate language processes.
Though thought disorders are not related to any other symptom of schizophrenia in particular, the type of thought disorder present during and immediately after an individual’s first psychotic episode can be indicative of which symptoms will persist at least 1 year later. Individuals who demonstrated deficits in semantic processing were likely to develop other dysorganised behaviours and actions. Those who experienced difficulties producing language were likely to have persistent negative symptoms. The ability of these individuals to plan tasks and maintain attention was an important indicator of their symptom severity, which again suggests that the dysfunction is not specific to language but to aspects of higher order thinking (Xu, et al., 2014).
Very little morphological or functional data has been collected in relation to thought disorders specifically. But one piece of research by Palaniyappan et al. (2015) did find morphological abnormalities in those who experienced negative thought disorders. The research found that severity of negative thought disorder correlated to increases in grey matter within an area important for error detection and decision making, the frontocingular region, and decreased grey matter in the striatum, insular and precuneus, which are important for some aspects of short term memory and movement. The more severe the negative thought disorder, the greater these changes were.
It is unclear exactly why thought disorders have such prominent effects upon language and speech production, or what it is causing the disorder, but progress is being made in the search for answers.
References
Speculative Neuroscience 