Reproducibility of functional MRI localization within the human somatosensory cortex

To evaluate the effect of fMRI localization approaches and region size on the reproducibility of digit localization in the human somatosensory cortex.

Vibrotactile stimulation was applied to digits 2 and 4 producing cortical activation sites relating to each digit. Thirteen subjects were scanned twice on separate occasions in a 3 Tesla scanner using a voxel size of 2 mm. Regions of activity were thresholded to different sizes varying from 50 to 1000 voxels. Three measures of position were acquired from these regions: center of gravity (COG), center co-ordinate and peak voxel. To account for registration errors, Euclidean distance between the two digits was computed. Reproducibility was determined in terms of the 95% confidence interval for individual position in X, Y, and Z and also the distance between the two digit locations.

Region size of 200 most significant voxels was shown to have the best reproducibility. Center co-ordinate proved to be the most precise form of localizing activity with a 95% CI of 2.1 mm, 2.6 mm, and 3.1 mm in the X, Y, and Z axes. Euclidean distance between the center co-ordinates of the two digit activation sites was shown to be a reliable means of overcoming registration errors with a 95% CI of 1.7 mm.

This study shows a high level of reproducibility for fMRI localization in the somatosensory system.