SILENT SPEECH ACTIVATES PREFRONTAL CORTICAL REGIONS ASYMMETRICALLY, AS WELL AS SPEECH-RELATED AREAS IN THE DOMINANT HEMISPHERE

Regional cerebral blood how (rCBF) was measured simultaneously over th e right and left hemispheres by 2 x 32 detectors in 30 healthy volunte ers with a two-dimensional iv xenon-133 technique, during (1) rest and during (2) audible and (3) silent counting (101, 102,...). Mean hemis phere CBF increased significantly in both hemispheres during the activ ations. Audible speech activated rolandic and temporoparietal regions mainly on the right side. This pattern covers auditory and para audito ry as well as motor (tongue/larynx) regions. Most likely those regions are involved in auditory feedback and voice control, Silent speech (i nternal speech) gave a clearly different activation pattern involving (1) left-sided regions related to speech perception and speech motor c ontrol (including the SMA) and (2) a right dorsolateral prefrontal are a that may be related to attention mechanisms. The silent speech patte rn appears to demonstrate aspects of internal (cognitive) feedback act ivity in which prefrontal cortical regions are activated significantly . Audible and silent counting may represent two principally different types of cerebral feedback systems, one for overt sensory-motor activi ty and one for a pure internal cognitive feedback. (C) 1996 Academic P ress, Inc.