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Imaging the cortical responses to quantised touch

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Abstract

Background Within the glabrous skin, touch is supported by mechanoreceptors, with most haptic sensations resulting from a combination of different mechanoreceptors being employed. These receptors can be broken down into two groups, those that are slowly-adapting (SAI, SAII), which detect changes in skin deformation (e.g. pressure), and those that are fast-adapting (FAI, FAII), which detect rapid fluctuations (e.g. vibration). A lot is known about the different receptors’ properties within the peripheral nervous system, but how these individual sensations are represented in the brain in humans has been investigated less. Here, we introduce the first known attempt to image these discrete responses using magnetoencephalography (MEG). Methods 9 participants volunteered to undergo a microneurography procedure, where a tungsten electrode was placed within the median nerve, and single mechanoreceptive afferents were recorded from. Once a single afferent had been identified, the participant received a small current (~5 μA, consisting of 60 200 μs pulses over 1 s) down the electrode to electrically-stimulate the same afferent identified physiologically. If there was a match, the participant underwent a scan using a 275-channel CTF MEG system in a synthetic 3rd order gradiometer configuration, where the same 1 s stimulation was repeated 80 times with ~10 s inter trial intervals. Data were frequency filtered between 13-30 Hz, and source localised using a beamformer and a 3-shell boundary element model. Pseudo-T statistical images were generated contrasting oscillatory power during stimulation against an epoch 8-9 seconds after stimulation. Results Across the cohort we recorded MEG data stimulating 19 mechanoreceptive afferents, and after quality control checks, we were left with 16 units (10 FAI, perceived sensation: point-like vibration; 5 SAI, perceived sensation: point-like pressure; 1 FAII, perceived sensation: diffuse vibration). A group analysis of the 10 FAI afferents show a significant event-related decrease in 13-30 Hz power during stimulation, with the largest change in power occurring in the postcentral gyrus. Permutation testing of the individual receptors’ images reveal that 8/10 of these receptors had significant reductions in power, which were all in spatial agreement with each other. Discussion In this investigation we have shown that it is possible to detect the spatial, temporal, and spectral properties of the cortical representations of individual mechanoreceptive afferents using MEG. Future investigations will interrogate how different afferent types manifest in the cortex in response to stimulation.
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Dates and versions

hal-02357769 , version 1 (13-11-2019)

Identifiers

  • HAL Id : hal-02357769 , version 1

Cite

George C O'Neill, Johan W Wessberg, Roger Watkins, Rochelle Ackerley, Eleanor L Barratt, et al.. Imaging the cortical responses to quantised touch. BIOMAG, Aug 2018, Philadelphia, United States. ⟨hal-02357769⟩
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