Reproducibility of functional MRI localization within the human somatosensory cortex

Abstract

Purpose: To evaluate the effect of fMRI localization approaches and region size on the reproducibility of digit localization in the human somatosensory cortex. Materials and Methods: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.Results: 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 coordinates 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.Conclusion: This study shows a high level of reproducibility for fMRI localization in the somatosensory system.

Re-wiring the brain: Increased functional connectivity within primary somatosensory cortex following synchronous co-activation

“…The digit localisation paradigm provided robust digit localisation in 24 out of the 29 participants for combined pre and post co-activation data. An area of 200 contiguous voxels was identified for D2 and D4 for each individual, based on previous work showing this size region to be highly reproducible (Vidyasagar and Parkes, 2011). Participants were excluded from subsequent analysis (3 participants from the synchronous and 2 participants from the asynchronous conditions, leaving 13 in the synchronous condition, including 10 returners, and 11 in the asynchronous condition) as they had failed to show 200 contiguously activated voxels at p < 0.01 uncorrected for both digits.…”

“…For each pre, post and return session, digit regions were defined following the approach described in a previous study (Vidyasagar and Parkes, 2011), which showed a high level of reproducibility across sessions. In brief, the t-statistic contrast maps were first thresholded to a significance level of p < 0.01, uncorrected, for visual inspection.…”

“…In brief, the t-statistic contrast maps were first thresholded to a significance level of p < 0.01, uncorrected, for visual inspection. A threshold of 200 voxels was set for identification of cortical activation sites for D2 and D4 based on findings from previous work (Vidyasagar and Parkes, 2011). Data were excluded from further analysis if they failed to show at least 200 contiguous voxels activated at this threshold for both digits.…”

“…This approach can determine the distance between two digit representations with a 95% confidence interval of 1.7 mm (Vidyasagar and Parkes, 2011). Paired student t -tests were performed to determine whether individual digit locations and the distance between digits changed following synchronous and asynchronous stimulation.…”

Distinct fine‐scale fMRI activation patterns of contra‐ and ipsilateral somatosensory areas 3b and 1 in humans

“…To date, most human S1 functional imaging studies have focused on the topographic organization of S1 cortex or its subdivisions [Nelson and Chen, 2008;Sanchez-Panchuelo et al, 2010;Schweisfurth et al, 2011;Schweizer et al, 2008;Vidyasagar and Parkes, 2011]. Few studies have examined the fine-scale functional organization of area 3b and area 1 in humans, partially due to the constraints of signal-or contrast-to-noise ratio of conventional imaging methods [Martuzzi et al, 2012;Sanchez-Panchuelo et al, 2012].…”