Separate neural subsystems within 'Wernicke's area'

Over time, both the functional and anatomical boundaries of 'Wernicke's are a' have become so broad as to be meaningless. We have re-analysed four func tional neuroimaging (PET) studies; three previously published and one unpub lished, to identify anatomically separable, functional subsystems in the le ft superior temporal cortex posterior to primary auditory cortex. From the results we identified a posterior stream of auditory processing, One part, directed along the supratemporal cortical plane, responded to both non-spee ch and speech sounds, including the sound of the speaker's own voice. Activ ity in its most posterior and medial part, at the junction with the inferio r parietal lobe, was linked to speech production rather than perception. Th e second, more lateral and ventral part lay in the posterior left superior temporal sulcus, a region that responded to an external source of speech. I n addition, this region was activated by the recall of lists of words durin g verbal fluency tasks. The results are compatible with an hypothesis that the posterior superior temporal cortex is specialized for processes involve d in the mimicry of sounds, including repetition, the specific role of the posterior left superior temporal sulcus being to transiently represent phon etic sequences, whether heard or internally generated and rehearsed. These processes are central to the acquisition of longterm lexical memories of no vel words.