Functional lateralization of human gustatory cortex related to handedness disclosed by fMRI study

Ten healthy subjects aged 20-25 including five right-handed and five left-handed according to the Dellatolas test participated in this functional magnetic resonance imaging (fMRI) study. A 3 Tesla whale-body MR scanner allowed echo planar imaging (EPI)-64 x 64 pixels, repetition time (TR)= 6 s, field of view (FOV)=20 x 20 cm(2)-associated to acute anatomical localization of activated foci (256 x 256 pixels). Subjects were bilaterally stimulated with NaCl 85 mM, aspartame 2 mM, quinine hydrochloride 1 mM, glycyrrhizic acid 0.5 mM, guanosine monophosphate 1 mM and D-threonine 250 mM alternating with water. Stimuli and rinse were continuously pushed as bolus of 50 mu l every 3 s to the subject's mouth through microsyringes. We detected brain activated areas by correlation of the MR signal to an on-line perception profile recorded for each experiment and each subject with the finger-span method. We found most activations in the insula and the perisylvian region in agreement with previous electrophysiological studies on monkey s and clinical reports in humans. The superior part of the insula was bilaterally activated, in accordance with a whole-month stimulation. A striking lateralization related to handedness was found in a lower part of the insula. This projection in the dominant hemisphere, located in the same coronal plane as the upper insular activation, is the first evidence of a functional lateralization of brain processing involved in taste perception.