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What is Formal Thought Disorder (FTD)? Formal thought disorder describes a communication phenomenon where the subject expresses their thought, through language (verbal or written) in a way that is considered disorganised, leading to a failure in communication.
Although the classic name given to this phenomenon refers to a disorder in the "form" (or the structure, rather than "content") of thought, the actual phenomenon involves expression through language and can be more directly described as "language disorganisation". The relationship between language and thought has been a topic of intense discussion. The thinking processes related to expressions in language are complex. At least some thinking processes may not be directly related to language (visuospatial and emotional processes). As a result, it would be more appropriate to describe formal thought disorder as language disorganisation.
FTD as a Clinical Sign in Psychiatry
FTD or Language organisation is a clinical "sign" rather than a "symptom". The patient usually does not actively complain of this difficulty in communication. In fact, the patient often behaves as if he or she is unaware of a communication problem. This is in contrast to neurological symptoms such as nominal dysphasia, in which patients can be aware of, and distressed by, language difficulties.
FTD is also a clinical sign that cannot be deliberately produced. Unlike symptoms that refer to aberrant subjective experiences, FTD can be observed by an external observer and is indeed detectable by a machine (see below). As such it stands apart from the many symptoms in psychiatry where assessment is entirely dependent on the patient's self-report. The presence of FTD therefore can be a more definite sign of a mental condition. FTD occurring in clear consciousness is a specific clinical sign. It is not seen in many conditions. Language disruption in acute confusional state is associated with a general reduction in arousal and a more generalised disengagement with the environment. FTD can also be observed in extreme tiredness and sleepiness as a transient phenomenon. FTD is also seldom seen in substance induced psychosis such as amphetamine induced psychosis, with overactivity of monoamines. FTD has been observed in phencyclidine induced psychosis where glutamate neurotransmission is affected. The observation of FTD in clear consciousness is therefore quite specific to psychosis, involving both schizophrenia spectrum psychosis and bipolar manic psychosis. However it is observed only in a proportion of patients with these conditions; its absence does not rule out these conditions. Whether FTD in schizophrenia and mania could be distinguishable from one another is controversial. Studies suggest that if contextual information (such as contents communicated) are removed, it would be difficult to distinguish schizophrenia and mania based on FTD alone. The value of FTD as a signal of psychopathology lies in its objectivity and specificity.
FTD Phenomena in a Psycholinguistic Framework
The clinical description of FTD in psychopathology has followed traditional nomenclature with definitions and examples. The following are typical examples: circumstantiality, tangentiality, poverty of content of speech, derailment, loosening of association, flight of ideas, clang association, and word salad. It is possible to organize these phenomena in a meaningful framework with the use of insights from modern psycholinguistics.
Psycholinguistics makes a distinction between language understanding processes and language production processes. FTD directly maps onto language production processes, and whether language understanding is also affected is a separate empirical question. Studies of FTD invoking the use of language perception paradiagms may have limited relevance because of this. Language production processes involve a hierarchy of cognitive processes translating ideations into actual linguistic expressions. The organisation in these linguistic levels can be distinguished in the following: (1) involving the use of individual words; (2) involving the use of phrases constructed from words; (3) involving the expression of a sequence of ideas; (4) involving sentences (with a noun-verb structure specific to a particular language); (5) involving the use of construction of discourse from sentences. This approach organizes phenomena according to the size of the disrupted linguistic unit from single lexical items, to adjacent units, to syntactically structured sentences, and to discourses based on multiple sentences. One hypothesis is that language disorganisation is not totally haphazard, but is expressed with reference to the underlying disturbance. For instance, in a milder general disturbance, only larger units with a long temporal span are affected (i.e. discourse direction become lost) while smaller units (sentences and lexical items) are used normally. With increasing severity of disturbance, smaller units (units within sentences) also become increasingly affected. The loss of syntax is a particularly poignant milestone as it is fundamental to sentential organisation. In fact, disorganisation of syntax leading to "word salad" is not often seen in mild to moderate forms of psychotic disorders.
The specificity of FTD also means that it is not easily encountered outside the clinical setting. Experience in observing and evaluating FTD requires actual clinical contact rather than learning from textbook descriptions. Intentional production of FTD is difficult for healthy individuals. This signifies that the brain has a default linguistic regularity that is difficult to override.
