Differentiation of somatosensory cortices by high-resolution fMRI at 7 T.

This study aimed to evaluate the ability of BOLD signals at high MRI field (7 T) to map fine-scale single-digit activations in subdivisions (areas 3b and 1) of the human primary somatosensory cortex (SI) in individual subjects. We acquired BOLD fMRI data from cortical areas around the central suclus in six healthy human subjects while stimulating individual finger pads with 2-Hz air puffs. Discrete, single-digit responses were identified in an area along the posterior bank of the central sulcus corresponding to area 3b and in an area along the crest of the postcentral gyrus corresponding to area 1. In single subjects, activations of digits 1 to 4 in both areas 3b and 1 were organized in a somatotopic manner. The separation of digit representations was measured for adjacent digits and was approximately 1.6 times greater in area 3b than in area 1. Within individual subjects, the cortical responses to single-digit stimulations and the magnitude of the BOLD signals were reproducible across imaging runs and were comparable across subjects. Our findings demonstrate that BOLD fMRI at 7 T is capable of revealing the somatotopic organization of single-digit activations with good within-subject reliability and reproducibility, and activation maps can be acquired within a reasonably short time window, which are essential characteristics for several neurological applications within patient populations.