Nuclear schizophrenic symptoms as a window on the relationship between thought and speech

Symptoms of schizophrenia known as 'nuclear' or 'first-rank' are found in all populations. The genetic variation that gives rise to them must be as old as modern Homo sapiens.

The hypothesis was formulated that language evolved, under constraints on callosal transmission, by a process of hemispheric specialisation. One component, the phonological output sequence, became localised to the dominant hemisphere whereas its associations (the signifieds) were lateralised in part to the non-dominant hemisphere. Concepts ('thoughts') are translated through a bi-hemispheric interaction into phonemes ('speech') by the speaker in frontal association areas, and decoded back into concepts ('meanings') by the hearer in occipitotemporo-parietal association areas.

The first-rank symptoms demonstrate that an integral component is a system of 'indexicality' that distinguishes those phonemic signals generated by the hearer, from his own thoughts, and from signals that he receives from an interlocutor.

Language, as Buehler proposed, is cast in a coordinate system orientated at its origin, in the dominant hemisphere, to the self of the speaker. Thus conceived, the phenomena of the illness called schizophrenia are key to the neural organisation of the human characteristic of language.