title: Somatotopic finger mapping using MEG: toward an optimal stimulation paradigm.
abstract: OBJECTIVE
  In non-invasive somatotopic mapping based on neuromagnetic source analysis, the recording time can be shortened and accuracy improved by applying simultaneously vibrotactile stimuli at different frequencies to multiple body sites and recording multiple steady-state responses. This study compared the reliability of sensory evoked responses, source localization performance, and reproducibility of digit maps for three different stimulation paradigms.
  
  
  METHODS
  Vibrotactile stimuli were applied to the fingertip and neuromagnetic steady-state responses were recorded. Index and middle fingers were stimulated either sequentially in separate blocks, simultaneously at different frequencies, or in alternating temporal order within a block.
  
  
  RESULTS
  Response amplitudes were largest and source localization was most accurate between 21 and 23 Hz. Separation of adjacent digits was significant for all paradigms in all participants. Suppressive interactions occurred between simultaneously applied stimuli. However, when frequently alternating between stimulus sites, the higher stimulus novelty resulted in increased amplitudes and superior localization performance.
  
  
  CONCLUSIONS
  When receptive fields are strongly overlapping, the alternating stimulation is preferable over recording multiple steady state responses.
  
  
  CONCLUSIONS
  The new paradigm improved the measurement of the distance of somatotopic finger representation in human primary somatosensory cortex, which is an important metric for neuroplastic reorganization after learning and rehabilitation training.
authors.affiliation: Rotman Research Institute, Baycrest Centre, Toronto, ON, Canada. sjamali@research.baycrest.org
authors.forename: Shahab
authors.initials: S
authors.lastname: Jamali
authors.forename: Bernhard
authors.initials: B
authors.lastname: Ross
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D005385:Fingers / Q000502:physiology*; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D013003:Somatosensory Cortex / Q000502:physiology*; D055815:Young Adult
keywords: 95% confidence interval; 95% confidence radius; ANOVA; CI(95); CR(95); D1; D2; Dipole modeling; ECD; EEG; Frequency tagging; GOF; ISI; ITI; I–S; L–M; MANOVA; MEG; Neuromagnetic source analysis; PCA; PSI; Pearson–Filon statistics; Primary somatosensory cortex; P–A; SEF; SI; SNR; SSR; Somatosensory steady-state response; Somatotopic organization; Vibrotactile stimulation; ZPF; analysis of variance; electroencephalography; equivalent current dipole; fMRI; functional magnetic resonance imaging; goodness of fit; index finger; inferior–superior; inter-stimulus interval; inter-train interval; lateral–medial; magnetoencephalography; middle finger; multivariate analysis of variance; posterior–anterior; pound per square inch; primary somatosensory cortex; principal component analysis; signal-to-noise ratio; somatosensory evoked magnetic field; steady-state response