Within-Digit Functional Parcellation of Brodmann Areas of the Human Primary Somatosensory Cortex Using Functional Magnetic Resonance Imaging at 7 Tesla

Abstract

The primary somatosensory cortex (S1) can be subdivided cytoarchitectonically into four distinct Brodmann areas (3a, 3b, 1, and 2), but these areas have never been successfully delineated in vivo in single human subjects. Here, we demonstrate the functional parcellation of four areas of S1 in individual human subjects based on high-resolution functional MRI measurements made at 7 T using vibrotactile stimulation. By stimulating four sites along the length of the index finger, we were able to identify and locate map reversals of the base to tip representation of the index finger in S1. We suggest that these reversals correspond to the areal borders between the mirrored representations in the four Brodmann areas, as predicted from electrophysiology measurements in nonhuman primates. In all subjects, maps were highly reproducible across scanning sessions and stable over weeks. In four of the six subjects scanned, four, mirrored, within-finger somatotopic maps defining the extent of the Brodmann areas could be directly observed on the cortical surface. In addition, by using multivariate classification analysis, the location of stimulation on the index finger (four distinct sites) could be decoded with a mean accuracy of 65% across subjects. Our measurements thus show that within-finger topography is present at the millimeter scale in the cortex and is highly reproducible. The ability to identify functional areas of S1 in vivo in individual subjects will provide a framework for investigating more complex aspects of tactile representation in S1.

Bringing transcranial mapping into shape: Sulcus-aligned mapping captures motor somatotopy in human primary motor hand area

“…Compared to the primary somatosensory hand area (S1 HAND ), the within-limb somatotopy in M1 HAND is less pronounced and lacks a strict sequential mediolateral ordering of the finger representations (Rathelot and Strick, 2006;Sanes et al, 1995). In the S1 HAND , the organization and processing of tactile inputs from the periphery show a relative strict arrangement along a mediolateral axis (Martuzzi et al, 2014;Nelson and Chen, 2008;Sanchez-Panchuelo et al, 2012). Nevertheless, consistent somatotopic gradients of representation have also been reported in M1 HAND (Beisteiner et al, 2001(Beisteiner et al, , 2004Gentner and Classen, 2006;Quandt et al, 2012) despite the widespread and intermingled neural populations in the primate M1 HAND controlling finger movements (Georgopoulos et al, 1999).…”

Exploring structure and function of sensory cortex with 7 T MRI

“…Cortical responses to tactile events have been difficult to measure using conventional fMRI experiments. In particular, the reliable localisation and subdivision of primary somatosensory cortex (S1) has been hard to achieve We have also demonstrated that it is possible to measure the finer-scale sub-divisions of S1, using within-digit organization (base-to-tip) stimulation of digits, providing functional parcellation of Brodmann areas of human S1 (Sanchez-Panchuelo, Besle et al 2012). We have assessed the relationship between these functional domains and underlying structure by inspecting our functionally parcellated Brodmann areas for differences in cortical thickness and alternative MR contrast measures.…”

Measuring temporal, spectral and spatial changes in electrophysiological brain network connectivity

“…mapped to separate areas of the body (Sanchez-Panchuelo et al, 2012)). Functional connections may be investigated between any pair of sub-regions within the sensori-motor network, and it is entirely conceivable that temporal nonstationarity between individual voxels, or small clusters, may be (in part) due to spatial inhomogeneity within the network.…”