fMRI assessment of hemispheric language dominance using a simple inner speech paradigm

Hemispheric language dominance (HLD) has been determined by means of functi onal MRI (fMRI) using a simple, inner speech, word fluency paradigm. During the task periods, subjects perform mental imagery of visual scenes acid ge nerate silently the nouns of all objects visualized. During the control per iods, subjects attend to the scanner noise. Activated areas have been ident ified by means of cross-correlation analysis. HLD indices have been determi ned by comparing the number of activated pixels detected in both hemisphere s within predefined cortical areas (Brodmann areas 6, 9, 10, 39, 40 and 44- 47). The paradigm has been assessed on 10 healthy, right-handed volunteers. A volume 35 mm thick, centered on the inferior frontal gyrus, was imaged. A conventional GRE MR sequence was used on a 1.5 T clinical MR scanner. HLD indices were compared with those determined for overt speech. Robust fMRI reponses were obtained. HLD indices indicated left hemispheric language dom inance for all subjects examined. They correlated well with those obtained for overt speech (R-2 = 0.93, regression coefficient = 0.998, with p < 10(- 4)). Thus, an inner speech paradigm based on visual imagery is well adapted for assessment of HLD by means of fMRT. Copyright (C) 1999 John Wiley & So ns, Ltd.