Brain activation in response to a tactile stimulation: functional magnetic resonance imaging (FMRI) versus cognitive...

Objective. The aim of this study was to compare fMRI analysis of somatosensory areas activated by passive touch, to cognitive analysis of the psychological profile of human subjects. Methods. The study was carried out on 21 females, after informed consent. Two artificial textures (smooth and rough), and two natural textures (the skin of an operator modified or not by a cosmetic product), were applied on the fingers of the subjects. A period of imagination to be touched was also included in the study. MR images of the somatosensory cortex were acquired on a 1.5T MRI system during the different behavioral conditions. Series of images were first processed to compensate for the inter-frame motions and then activation was assessed with a statistical method based on conditional analysis. After the MRI protocol, each subject was interviewed following a questionnaire from which psychological descriptors were extracted. Results. 1) Activations were quite similar for all textures in the contralateral sensory areas 2) In the ipsilateral sensory areas, activations were more important in response to a stimulation with the skin of an operator than with artificial textures. The activation was even more important after application of a cosmetic product on the skin. 3) Imagination of the tactile stimulation resulted in an activation mostly localized in the ipsilateral cortex. 4) A PLS analysis assessed that 2 psychological descriptors, rationality and sensorial reactivity, were related to an activation in the contralateral cortex, while 2 others, imagination and sensitivity, were related to ipsilateral areas activation. Conclusion. fMRI and cognitive analysis allowed us to map the physical component of the tactile perception in the contralateral cortex. This study also gave rise to a better understanding of the activation in ipsilateral areas, which was found to be mainly related to the subjective component of the stimulation.