Somatotopy in the Human Somatosensory System.

Rosa M Sanchez Panchuelo,Miles Humberstone,Susan Francis,Julien Besle,Denis Schluppeck

doi:10.3389/fnhum.2018.00235

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.

Highlights

With the advent of ultra-high-field (UHF) MR scanners operating at 7 Tesla (7T) and above, high spatial resolution functional Magnetic Resonance Imaging has been used to study the somatotopic representation of individual digits of the hand in the posterior bank of the central sulcus, corresponding to the location of primary somatosensory cortex (SI), in individual human subjects (Sánchez-Panchuelo et al, 2010; Stringer et al, 2011; Besle et al, 2014; Martuzzi et al, 2014; Kolasinski et al, 2016)
UHF functional Magnetic Resonance Imaging (fMRI) has been shown to provide the spatial resolution required to resolve within-digit somatotopy, demonstrating the subdivision of cytoarchitectonic areas of SI based on functional criteria (Sánchez-Panchuelo et al, 2012, 2014) and to resolve activations of the leg and foot in Brodmann area subdivisions of SI (Akselrod et al, 2017)
The three middle digits are not independently resolved in SII, but the phase reflects a preference for Digit 3, which was stimulated between Digits 2 and 4

Summary

Introduction

With the advent of ultra-high-field (UHF) MR scanners operating at 7 Tesla (7T) and above, high spatial resolution functional Magnetic Resonance Imaging (fMRI) has been used to study the somatotopic representation of individual digits of the hand in the posterior bank of the central sulcus, corresponding to the location of primary somatosensory cortex (SI), in individual human subjects (Sánchez-Panchuelo et al, 2010; Stringer et al, 2011; Besle et al, 2014; Martuzzi et al, 2014; Kolasinski et al, 2016). A subsequent fMRI study (Eickhoff et al, 2007) correlated the functional somatotopic maps with cytoarchitectonic areas OP1 and OP4, and concluded that these two areas constitute the human homologous of SII and PV, respectively, with OP3 the most possible homologue to VS

Methods

Results

Conclusion