Language activation studies with positron emission tomography.

Behavioural tasks produce changes in regional cerebral blood flow (rCBF), the result of increased local neural activity. These changes can be measured with positron emission tomography (PET). Language activation studies by means of PET are being used to relate regional patterns of cerebral activation to information-processing models of speech and reading. Significant activation confined to both superior temporal gyri has been observed when normal subjects hear words played backwards, listen to non-words, and perform category judgements on pairs of heard real words. Prestriate cortex is activated by seeing strings of letter-like symbols, consonant strings, pronounceable non-words and real words, with additional activation in left medial prestriate cortex in response to the non-words and real words. Left posterior superior temporal gyrus (PSTG), left dorsolateral prefrontal cortex (DLPFC) and supplementary motor area (SMA) are engaged when subjects retrieve verbs from memory to match nouns. Finally, primary sensorimotor cortex is activated during articulation. There is particular interest at present in the precise roles of left PSTG and DLPFC in single-word comprehension and generation, and interpretation of the results depends critically on the design of the single-word tasks used for behavioural activation.