Somatotopy in the Human Somatosensory System

Abstract

Previous functional magnetic resonance imaging (fMRI) studies have demonstrated digit somatotopy in primary somatosensory cortex (SI), and even shown that at high spatial resolution it is possible to resolve within-digit somatotopy. However, fMRI studies have failed to resolve the spatial organisation of digit representations in secondary somatosensory cortex (SII). One of the major limitations of high spatial resolution fMRI studies of the somatosensory system has been the long acquisition time needed to acquire slices spanning both SI and SII. Here, we exploit the increased blood oxygenation level dependent contrast of ultra-high-field (7 Tesla) fMRI and the use of multiband imaging to study the topographic organisation in SI and SII with high spatial resolution at the individual subject level. A total of n = 6 subjects underwent vibrotactile stimulation of their face, hand digits and foot (body imaging) and their individual hand digits (digit mapping) for each left and right sides of the body. In addition, n = 2 subjects participated only in the body imaging experiment on both their left and right sides. We show an orderly representation of the face, hand digits and foot in contralateral primary cortex in each individual subject. In SII, there is clear separation of the body areas of the face, hand and foot but the spatial organisation varies across individual subjects. However, separate representation of the individual digits of the hand in SII could not be resolved, even at the spatial resolution of 1.5 mm due to largely overlapping representations.

Somatotopic Arrangement of Eight Distinct Skin Areas in the Human Primary Somatosensory Cortex Derived from Functional Magnetic Resonance Imaging

“…For most of the participants, the forehead region of the somatosensory cortex lies deep within the postcentral sulcus in a region between the lower limb and upper limb area. This finding is consistent with a study on the facial representation on SI in macaques [21], as well as a recent fMRI study at 7 T which showed cortical activations in the same area upon cheek stimulation [35].…”

“…As seen in Table [cortical mag] the pial surface area of voxels that were correlated with0. 35 to the finger stimulus timing was on the order of 10 cm2 for 4 out of 6 of the people scanned, nearly 25% of the total surface area of the postcentral gyrus and sulcus. For participant F, the surface area was about 15% less, while for participant D, the surface area was only 3 cm 2 .…”

“…The device simulates the action of a Wartenberg pinwheel [33] over a small area of skin, but is made of plastic and does not puncture the skin or elicit pain. The device was fully automated and was synchronized to the acquisition of fMRI data, which enabled the use of analytical techniques based on stimulus timing and temporal correlation that have been used to study topographic maps of the visual and somatosensory systems [34,35].…”

Moving in on human motor cortex. Characterizing the relationship between body parts with non-rigid population Response Fields

“…It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted November 15, 2020. ; https://doi.org/10.1101/2020.11.12.379339 doi: bioRxiv preprint to consist of two separate regions: pre-SMA and SMA proper [35,36], which might each represent the whole body in full. The region denoted insula, which covers the region enclosed by the Sylvian fissure up to the parietal operculum, likely contains the secondary somatosensory cortex (S2), which is believed to contain a whole-body somatotopy as well [37][38][39]. The selection of regions of interest (ROI) often is an arbitrary and non-trivial process, which could be aided in future studies by the current pRF center results.…”

Passive perceptual learning modulates motor inhibitory control in superior frontal regions

“…It was considered the methodologically most appropriate alternative to have exact the same set up for both groups except of varying the administration of the stimulation protocol. A control stimulation at the same hand was excluded since it could still have interfered with the relevant stimulation site due to potentially overlapping cortical representations (Ackerley & Kavounoudias, ; Kalberlah et al, ; Sanchez Panchuelo, Besle, Schluppeck, Humberstone, & Francis, ). Conducting the control stimulation on the other hand was also not an option because transcallosal connections between homologous somatosensory regions as well as nonhomologous regions (Tamè, Braun, Holmes, Farnè, & Pavani, ) could have a potential effect on the results.…”