Serial aspects of language and speech related to prefrontal cortical activity. A selective review

Language and speech depend basically upon complex serial (i.e., sequential or temporally structured) neuronal events (action programs) which enable a perception of symbols and a production of meaningful words and sentences with adequate syntax and semantic content. There is evidence that action programs for speech and language, like other serial programs of the CNS, are handled specifically by the prefrontal cortex. Measurements of regional cerebral blood flow (rCBF) and metabolic rate (rCMR) support this view. Word perception, speech, reading etc. activate circumscribed areas in different patterns both in postcentral (afferent) and in precentral/prefrontal (efferent) regions of the hemisphere cortices. Most of these patterns show important symmetrical features. The classical speech cortices of Wernicke and Broca are not unconditionally activated in rCBF measurements during speech reception and production, respectively. Upper prefrontal activations are recorded during e.g. serial word production and reading, and during word perception lower prefrontal activations are seen in addition to postcentral increases of rCBF. A selective activation of prefrontal regions only, takes place during serial information processing related to cognition and ideation, including inner silent speech. In patients with cerebrovascular disorders, organic dementia, Parkinson's disease, and schizophrenia, various types of prefrontal (and other) rCBF and rCMR abnormalities may be seen. In such states different forms of "aseriality" or "dysseriality" (i.e., a defective serial programming) of speech can be recognized, which include non-fluent forms of aphasia of the Broca type, the hesitant, reduced and sometimes aprosodic speech in organic dementia and Parkinson's disease, as well as the peculiar semantic and motor disturbances of speech in schizophrenia.