R. M. Sanchez-Panchuelo, S. Francis, R. Bowtell and D. Schluppeck J Neurophysiol 103:2544-2556, 2010. First published Feb 17, 2010; doi:10.1152/jn.01017.2009 You might find this additional information useful... This article cites 60 articles, 12 of which you can access free at: http://jn.physiology.org/cgi/content/full/103/5/2544#BIBL Updated information and services including high-resolution figures, can be found at: http://jn.physiology.org/cgi/content/full/103/5/2544 Additional material and information about Journal of Neurophysiology can be found at: http://www.the-aps.org/publications/jn This information is current as of June 1, 2010 . Downloaded from jn.physiology.org on June 1, 2010 Journal of Neurophysiology publishes original articles on the function of the nervous system. It is published 12 times a year (monthly) by the American Physiological Society, 9650 Rockville Pike, Bethesda MD 20814-3991. Copyright © 2005 by the American Physiological Society. ISSN: 0022-3077, ESSN: 1522-1598. Visit our website at http://www.the-aps.org/. J Neurophysiol 103: 2544–2556, 2010. First published February 17, 2010; doi:10.1152/jn.01017.2009. Mapping Human Somatosensory Cortex in Individual Subjects With 7T Functional MRI R. M. Sanchez-Panchuelo,1 S. Francis,1 R. Bowtell,1 and D. Schluppeck2 1Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy and 2Visual Neuroscience Group, School of Psychology, University of Nottingham, Nottingham, United Kingdom Submitted 19 November 2009; accepted in final form 15 February 2010 Sanchez-Panchuelo RM, Francis S, Bowtell R, Schluppeck D. are being revisited. Several fMRI studies have investigated the Mapping human somatosensory cortex in individual subjects with 7T cortical representation of the hand using pneumatic or piezo- functional MRI. J Neurophysiol 103: 2544–2556, 2010. First pub- electric stimuli applied to the glabrous skin of the fingertips lished February 17, 2010; doi:10.1152/jn.01017.2009. Functional magnetic resonance imaging (fMRI) is now routinely used to map the (Duncan and Boynton 2007; Francis et al. 2000; Huang and topographic organization of human visual cortex. Mapping the de- Sereno 2007; Overduin and Servos 2008; Schweizer et al. tailed topography of somatosensory cortex, however, has proven to be 2008; Weibull et al. 2008). However, the spatial resolution of more difficult. Here we used the increased blood-oxygen-level-depen- the cortical maps produced in most of these studies is limited dent contrast-to-noise ratio at ultra-high field (7 Tesla) to measure the by the use of large voxel sizes or normalization and averaging Downloaded from topographic representation of the digits in human somatosensory of results across subjects (Francis et al. 2000; Gelnar et al. cortex at 1 mm isotropic resolution in individual subjects. A “traveling 1998; Kurth et al. 2000; Maldjian et al. 1999; Nelson and Chen wave” paradigm was used to locate regions of cortex responding to periodic tactile stimulation of each distal phalangeal digit. Tactile 2008; Overduin and Servos 2008; Weibull et al. 2008). stimulation was applied sequentially to each digit of the left hand from Ultra-high magnetic field (7T) provides access to fMRI data thumb to little finger (and in the reverse order). In all subjects, we with high-spatial resolution and high signal-to-noise ratio found an orderly map of the digits on the posterior bank of the central (SNR). Resolution is particularly important when studying jn.physiology.org sulcus (postcentral gyrus). Additionally, we measured event-related somatosensory cortex as maps of the body surface in S1 (even responses to brief stimuli for comparison with the topographic map- the relatively over-represented maps of the finger tips) are ping data and related the fMRI responses to anatomical images small, and the postcentral gyrus (PCG) is prone to significant obtained with an inversion-recovery sequence. Our results have im- portant implications for the study of human somatosensory cortex and partial volume effects (PVE) due to its large surface-to-volume underscore the practical utility of ultra-high field functional imaging ratio (Scouten et al. 2006) and narrow width (Fischl and Dale with 1 mm isotropic resolution for neuroscience experiments. First, 2000) as well as the interdigitation of the pre- and postcentral on June 1, 2010 topographic mapping of somatosensory cortex can be achieved in 20 gyri (White et al. 1997). Achieving high-spatial resolution min, allowing time for further experiments in the same session. generally means compromising blood-oxygenation-level-de- Second, the maps are of sufficiently high resolution to resolve the pendent (BOLD) contrast-to-noise ratio (CNR), volume cov- representations of all five digits and third, the measurements are erage, or temporal resolution. Statistical power can thus be- robust and can be made in an individual subject. These combined come limiting at lower field, particularly for sensory tasks advantages will allow somatotopic fMRI to be used to measure the where the BOLD signal is low in comparison with visual and representation of digits in patients undergoing rehabilitation or plastic motor tasks, even with a large number of repeated measure- changes after peripheral nerve damage as well as tracking changes in normal subjects undergoing perceptual learning. ments (Schweizer et al. 2008). 7T provides increased BOLD sensitivity (Gati et al. 1997; Van der Zwaag et al. 2009; Yacoub et al. 2001), which can be INTRODUCTION exploited to improve the spatial resolution and/or reduce the number of trials. Higher spatial specificity can also be achieved High resolution measurements of the somatotopic mapping in gradient echo (GE) BOLD data at 7T due to the attenuation of the hand in human cerebral cortex are important for under- of intravascular signal from veins (Gati et al. 1997; Ogawa standing disturbed sensory representations in neurological dis- et al. 1998; van der Zwaag et al. 2009; Yacoub et al. 2001). orders (Butterworth et al. 2003) and for tracking cortical However, the extravascular signal from venules and large veins re-organization in rehabilitation following peripheral nerve that immediately drain the capillary bed may still cause some damage or stroke. Precise knowledge of the spatial layout of spread of the BOLD response. primary somatosensory cortex (S1) is also crucial for under- Here we used fMRI at ultra-high field (7 T) to generate standing how top-down influences, such as attention, modulate complete high-resolution maps of the digit representations in sensory inputs to cortex. the primary somatosensory cortex (S1) in individual subjects. Penfield was the first to map human somatosensory cortex We aimed to maximize efficiency in mapping all five digits and perioperatively (Penfield and Boldrey 1937). With the advent to assess the use of a “traveling wave” paradigm as has been of noninvasive neuroimaging techniques, such as functional widely applied to retinotopic mapping (Engel et al. 1994, 1997; magnetic resonance imaging (fMRI), these early measurements reviewed in Wandell et al. 2007); a similar approach was first Address for reprint requests and other correspondence: D. Schluppeck, used in the somatosensory system to map the ventral surface of Visual Neuroscience Group, School of Psychology, University of Nottingham, the left arm (Servos et al. 1998). In addition, we validated the Nottingham, NG7 2RD UK (E-mail: [email protected]). traveling wave activity against a simple event-related protocol, 2544 0022-3077/10 Copyright © 2010 The American Physiological Society www.jn.org MAPPING HUMAN SOMATOSENSORY CORTEX 2545 assessed the contribution of different tissues to the measured scan parameters: SENSE factor 2 in the right-left direction, TE ϭ 25 responses, and characterized the temporal properties of the ms, flip angle FA ϭ 90°, TR ϭ 2.4 s. A total of 22 contiguous axial event-related fMRI response in S1. slices spanning the right primary somatosensory cortex were acquired The results reveal a robust, consistent map of digit repre- with 1 mm isotropic resolution and a field of view (FOV) of 192 mm sentations in individuals along the posterior aspect of the in the anterior-posterior (AP) direction and 72 mm in the right-left (RL) direction. The reduced FOV in the phase encoding direction central sulcus. In contrast to several previous studies that (RL) required the use of outer-volume suppression (OVS) (Pfeuffer inferred cytoarchitectonic subregions by the existence of iso- et al. 2002) to prevent signal fold-over. The locations of the imaging lated peaks in thresholded statistical maps, our data show no stack and OVS slab are shown in Fig. 3A for a representative subject. such clear segregation (see e.g., Nelson and Chen 2008). Magnetic field inhomogeneity was minimized by using a local, image- based shimming approach (Poole and Bowtell 2008; Wilson et al. 2002). This involved generating a B0-field map from the difference in METHODS ϭ phase of two gradient echo images with echo times of TE1 6msand ϭ Subjects TE2 6.5 ms; skull-stripping the B0-field map (BET, FSL) (Smith 2002) so that field optimization could be focused on brain regions; and Five subjects experienced in fMRI experiments participated in this determining the shim coil currents up to second order needed to study with written consent. Procedures were conducted with approval minimize the field inhomogeneity inside a cuboidal region containing from the University of Nottingham ethics committee. Each subject the central sulcus (highlighted in Fig. 3A). The shim calculation took participated in three scan sessions: two sessions at 7T, one session to Ͻ30 s (Matlab R2007, 2.0 GHz Pentium 4 processor). The efficacy of measure the topographic representation of digits in the somatosensory the image-based shimming procedure was compared with that of the cortex with a traveling wave paradigm, and one session to characterize FASTMAP approach (Gruetter 1993) as implemented on the Philips the spatial and temporal properties of responses to vibrotactile digit scanner, by acquiring B0-field maps and EP images after shimming on Downloaded from stimulation in an event-related task design.