title: Validation of periodic fMRI signals in response to wearable tactile stimulation.
abstract: To map cortical representations of the body, we recently developed a wearable technology for automatic tactile stimulation in human functional magnetic resonance imaging (fMRI) experiments. In a two-condition block design experiment, air puffs were delivered to the face and hands periodically. Surface-based regions of interest (S-ROIs) were initially identified by thresholding a linear statistical measure of signal-to-noise ratio of periodic response. Across subjects, S-ROIs were found in the frontal, primary sensorimotor, posterior parietal, insular, temporal, cingulate, and occipital cortices. To validate and differentiate these S-ROIs, we develop a measure of temporal stability of response based on the assumption that a periodic stimulation evokes stable (low-variance) periodic fMRI signals throughout the entire scan. Toward this end, we apply time-frequency analysis to fMRI time series and use circular statistics to characterize the distribution of phase angles for data selection. We then assess the temporal variability of a periodic signal by measuring the path length of its trajectory in the complex plane. Both within and outside the primary sensorimotor cortex, S-ROIs with high temporal variability and deviant phase angles are rejected. A surface-based probabilistic group-average map is constructed for spatial screening of S-ROIs with low to moderate temporal variability in non-sensorimotor regions. Areas commonly activated across subjects are also summarized in the group-average map. In summary, this study demonstrates that analyzing temporal characteristics of the entire fMRI time series is essential for second-level selection and interpretation of S-ROIs initially defined by an overall linear statistical measure.
authors.affiliation: Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Ching-Fu
authors.initials: CF
authors.lastname: Chen
authors.affiliation: Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, CA 92093, USA; Institute for Neural Computation, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Kreutz-Delgado
authors.affiliation: Birkbeck/UCL Centre for NeuroImaging (BUCNI), London WC1E 7HX, UK; Department of Psychology and Neuroimaging Center, San Diego State University, San Diego, CA 92182, USA.
authors.forename: Martin I
authors.initials: MI
authors.lastname: Sereno
authors.affiliation: Institute for Neural Computation, University of California, San Diego, La Jolla, CA 92093, USA. Electronic address: rhuang@ucsd.edu.
authors.forename: Ruey-Song
authors.initials: RS
authors.lastname: Huang
mesh_terms: D001931:Brain Mapping / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D010812:Physical Stimulation / Q000295:instrumentation*; D066191:Sensorimotor Cortex / Q000502:physiology*; D000076251:Wearable Electronic Devices; D055815:Young Adult
keywords: Human somatotopy; Linear systems analysis; Signal stability; Time-frequency analysis; Wearable tactile stimulation