Cortical Characterization and Inter-Dipole Distance Between Unilateral Median Versus Ulnar Nerve Stimulation of Both Hands in MEG

Abstract

Contralateral somatosensory evoked fields (SEF) by whole head MEG after unilateral median and ulnar nerve stimulation of both hands were studied in 10 healthy right-handed subjects. Major parameters describing cortical activity were examined to discriminate median and ulnar nerve evoked responses. Somatic sensitivity showed high similarity in the 4 study conditions for both hand and nerve. The brain SEFs consisted of 7-8 major peak stages with consistent responses in all subjects at M20, M30, M70 and M90. Comparable inter-hemispheric waveform profile but high inter-subject variability was found. Median nerve induced significantly shorter latencies in the early activities than those of the ulnar nerve. The 3D cortical maps in the post stimulus 450 ms timeframe showed for both nerves two polarity reversals, an early and a late one which is a new finding. Dipole characteristics showed differential sites for the M20 and M30 in the respective nerve. Higher dipole moments evoked by the median nerve were noticed when compared to the ulnar. Furthermore, the results of the dipole distances between both nerves for M20 were calculated to be at 11.17 mm +/- 4.93 (LH) and 16.73 mm +/- 5.66 (RH), respectively after right hand versus left hand stimulation. This study showed substantial differences in the cortical responses between median and ulnar nerve. Especially the dipole distance between median and ulnar nerve on the cortex was computed accurately for the first time in MEG. Little is known however of the cortical responses in chronic pain patients and the parameter(s) that may change in an individual patient or a group. These results provide precise basis for further evaluating cortical changes in functional disorders and disease sequelae related to median and ulnar nerves.

Imaging somatosensory cortex responses measured by OPM-MEG: Variational free energy-based spatial smoothing estimation approach

“…Using the constructed wearable OPM-MEG, we have shown that the SEFs under median and ulnar nerve stimulations can be reliably detected by OPMs with high quality (maximum amplitude reaches 1 pT). Both the sensor-level and source-level analyses have demonstrated substantial differences in cortical responses to different stimulations of peripheral nerves, which is consistent with the findings of previous studies ( Theuvenet et al., 2006 ; Huttunen et al., 2006 ). In particular, FESSE provides more reasonable source imaging results than competing methods without adjusting the imaging threshold ( Figure 8 ).…”

Anesthetic Block of Pain-related Cortical Activity in Patients with Peripheral Nerve Injury Measured by Magnetoencephalography

“…Polarity reversals of the three-dimensional brain maps mainly reflect change in dipole orientation and are an indication of spatial somatosensory processing. The first and second polarity reversals, consistently seen in the three-dimensional maps in subjects and described earlier, 63 differed in the two groups. The significance of the finding is that in the patient group both reversals were less consistently observed and moreover at different latencies is yet unknown.…”

Sensory Handedness is not Reflected in Cortical Responses After Basic Nerve Stimulation: A MEG Study

“…3D cortical mapping revealed dipolar fields at the major peak latencies with an early and late polarity reversal for both nerves, the significance for brain processing and accurate somatotopic organization is unknown but was observed earlier (Theuvenet et al 2006). The spatial dipole Fig.…”