COGNITIVE NEUROANATOMY OF LANGUAGE - CONT RIBUTION OF FUNCTIONAL CEREBRAL IMAGING

This review summarizes the main results obtained to date, concerning t he issue of brain/language relationships, from studies using the moder n techniques of in vivo functional imaging of the brain, namely Positr on Emission Tomography (PET) and, to a lesser extent, the still experi mental method of functional Magnetic Resonance Imaging. These studies mostly rely on the so-called cognitive activation paradigm, which cons ists of recording blood flow variations as measured in PET in normal v olunteers during various linguistic tasks compared to reference tasks. Since the late 80's, a great deal of literature has been accumulating , including studies of various aspects of language functions: perceptu al (auditory and visual) processing of linguistic materials, expressio n, verbal memory, semantics... The first few results obtained have alr eady led to challenge some previously widely held dogmas, derived from classical anatomoclinical studies, such as the role of Wernicke's are a in verbal comprehension and the role of Broca's area in language pro duction. The involvement of the left supramarginal gyrus in some aspec ts of phonological processing has been directly demonstrated. At the s ame time, some studies have yielded unexpected results suggesting, for instance, a special role for the inferior laternal parts of the left frontal lobe in semantic and/or voluntary aspects of language processi ng and episodic verbal memory. Among other studies, those concerning t he mechanisms of verbal short-term memory have provided interesting pa rallels with cognitive models. The demonstration, under certain experi mental conditions, of an involvement of hitherto unsuspected cortical regions (such as the insular or the temporopolar cortices) is of poten tial considerable importance. Finally, with current technical improvem ents of the imaging methods, it will be shortly possible to take into account the important issue of interindividual variations as well as t o perform activation studies in brain-damaged patients.