Event‐related fMRI at 7T reveals overlapping cortical representations for adjacent fingertips in S1 of individual subjects

Abstract

Recent fMRI studies of the human primary somatosensory cortex have been able to differentiate the cortical representations of different fingertips at a single-subject level. These studies did not, however, investigate the expected overlap in cortical activation due to the stimulation of different fingers. Here, we used an event-related design in six subjects at 7 Tesla to explore the overlap in cortical responses elicited in S1 by vibrotactile stimulation of the five fingertips. We found that all parts of S1 show some degree of spatial overlap between the cortical representations of adjacent or even nonadjacent fingertips. In S1, the posterior bank of the central sulcus showed less overlap than regions in the post-central gyrus, which responded to up to five fingertips. The functional properties of these two areas are consistent with the known layout of cytoarchitectonically defined subareas, and we speculate that they correspond to subarea 3b (S1 proper) and subarea 1, respectively. In contrast with previous fMRI studies, however, we did not observe discrete activation clusters that could unequivocally be attributed to different subareas of S1. Venous maps based on T2*-weighted structural images suggest that the observed overlap is not driven by extra-vascular contributions from large veins. Hum Brain Mapp 35:2027–2043, 2014. © 2013 The Authors Human Brain Mapping published by Wiley Periodicals, Inc.

Exploring structure and function of sensory cortex with 7 T MRI

“…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. We evaluated both magnetization transfer ratio (MTR) and signal intensity in phase sensitive inversion recovery (PSIR) images that are sensitive to the pattern of myelination (Sanchez-Panchuelo, Besle et al 2014). In this study, we showed consistent, area-related differences in cortical thickness and MTR/PSIR measurements across subjects.…”

“…For example, in our initial event-related experiments to measure cortical responses to vibrotactile stimulation of each of the fingertips and the overlap of cortical representations, we used > 30 trials per condition for generalized linear model (GLM) or deconvolution analyses (Besle, Sanchez-Panchuelo et al 2013, Besle, Sanchez-Panchuelo et al 2014. By combining data across many trials in which the signals are consistent, but unwanted contributions from noise are uncorrelated, such signal averaging allowed robust estimation of responses.…”

Relationships between cortical myeloarchitecture and electrophysiological networks

“…The general finding is that primary sensory cortices tend to be heavily myelinated whereas regions associated with multisensory integration are less myelinated (10,13). More localized spatial changes in myelination also exist; for example, subtle subdivisions between regions are apparent in visual (14,15), somatosensory (16), and auditory (17) cortices. There is evidence of cross-species changes in myelination (18), with the brains of nonhuman primates more heavily myelinated than those of humans.…”

Modulation of somatosensory perception and multisensory integration as a function of habitual patterns of action

“…I speculate differences in overlap, as suggested by the results of Besle et al (2014) should indeed exist in humans, though this has not yet been demonstrated statistically.…”

“…For example, the middle and ring fingers were found to have a much larger area of overlap than the middle and index fingers. Besle et al (2014) suggest previous mapping studies may have failed to detect overlap in area 3b (resulting in an overly segregated view of finger representations) due to experimental design, e.g., fMRI…”