Digit somatotopy in the human cerebellum: A 7 T fMRI study Wietske van der Zwaag a, b, ⁎, Remy Kusters b , Arthur Magill a, b , Rolf Gruetter a, b, c , Roberto Martuzzi d, e , Olaf Blanke d, e , José P. Marques a a Department of Radiology, University of Lausanne, Switzerland b Laboratory for Functional and Metabolic Imaging (LIFMET), Ecole Polytechnique Fédérale de Lausanne, Switzerland c Department of Radiology, University of Geneva, Switzerland d Laboratory of Cognitive Neuroscience (LNCO), Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne, Switzerland e Center for Neuroprosthetics, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, Switzerland abstract article info Article history: Accepted 16 November 2012 Available online 11 December 2012 Keywords: Cerebellum Somatosensory fMRI High resolution The representation of the human body in the human cerebellum is still relatively unknown, compared to the well-studied homunculus in the primary somatosensory cortex. The investigation of the body representation in the cerebellum and its somatotopic organisation is complicated because of the relatively small dimensions of the cerebellum, compared to the cerebrum. Somatotopically organised whole-body homunculi have previously been reported in both humans and rats. However, whether individual digits are represented in the cerebellum in a somatotopically organised way is much less clear. In this study, the high spatial resolution and high sensitivity to the blood oxygenation level dependent (BOLD) signal of 7 T fMRI were employed to study the BOLD responses in the human cerebellum to the stroking of the skin of individual digits, the hand and forearm. For the first time, a coarse somatotopic organisation of the digits, ordered from D1–D5, could be visualised in in- dividual human subjects in both the anterior (lobule V) and the posterior (lobule VIII) lobes of the cerebellum using a somatosensory stimulus. The somatotopic gradient in lobule V was found consistently in the posterior to anterior direction, with the thumb most posterior, while the direction of the somatotopic gradient in lobule VIII differed between subjects. No somatotopic organisation was found in Crus I. A comparison of the digit patches with the hand patch revealed that the digit regions are completely covered by the hand region in both the anterior and posterior lobes of the cerebellum, in a non-somatotopic manner. These results demonstrate the promise of ultra-high field, high-resolution fMRI for studies of the cerebellum. © 2012 Elsevier Inc. All rights reserved. Introduction Digit somatotopy in the primary somatosensory cortex has recently been demonstrated at ultra-high field (Martuzzi et al., 2012; Sanchez- Panchuelo et al., 2010; Stringer et al., 2011), but digit mapping in the cerebellum, while more challenging because of the spatial dimensions, is also of interest because of the importance of the cerebellum in the somatosensory-motor feedback loop (Granziera et al., 2009; Lu et al., 2007). Anatomically, the cerebellum is divided in three lobes, which in turn are further subdivided into lobules (Schmahmann et al., 1999). The anterior lobe contains lobules I–V, the posterior lobe lobules VI–IX and the flocculonodular lobe contains lobule X (Fig. 1A). Lobule VII is again subdivided into Crus I, Crus II and lobule VIIB. Lobules I–V in the anterior lobe and lobule VIII in the posterior lobe are involved in sensorimotor tasks (Manto et al., 2012; Stoodley and Schmahmann, 2009, 2010). Somatotopic body representations were first found in lobules IV–VI in Rhesus monkeys (Adrian, 1943) and subsequently in lobule VIII in cats (Snider and Stowell, 1944). These early cerebellar somatotopy ex- periments already reported that some neurons in the cerebellum have very small receptive fields on the body — as small as the side of a single toe in a monkey (Adrian, 1943) or individual whiskers in rats (Shambes et al., 1978). In rats, large parts of the cerebellar “homunculus” are dedicated to the whiskers because of their importance for exploratory actions (Shambes et al., 1978). The importance of the digits for human exploratory action suggests that the human cerebellar digit representa- tions will also be relatively large compared to their actual physical size. Somatosensory mapping of the digit representations in the cerebel- lum with fMRI has not been frequently attempted because of the relatively small size of the cerebellum, the high level of foliation, which emphasizes inter-subject variability and complicates group studies, and the small size of the finger representations compared to those found in the primary somatosensory cortex. In addition to the high level of foliation, the cerebellar grey matter layer is 3–5 fold thinner than the cerebral grey matter sheet (Marques et al., 2010b), further complicating NeuroImage 67 (2013) 354–362 ⁎ Corresponding author at: Station 6, EPFL SB LIFMET, 1015 Lausanne, Switzerland. Fax: + 41 21 693 7960. E-mail addresses: wietske.vanderzwaag@epfl.ch (W. van der Zwaag), r.kusters@student.tue.nl (R. Kusters), Arthur.magill@epfl.ch (A. Magill), rolf.gruetter@epfl.ch (R. Gruetter), Roberto.martuzzi@epfl.ch (R. Martuzzi), olaf.blanke@epfl.ch (O. Blanke), jose.marques@epfl.ch (J.P. Marques). 1053-8119/$ – see front matter © 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.neuroimage.2012.11.041 Contents lists available at SciVerse ScienceDirect NeuroImage journal homepage: www.elsevier.com/locate/ynimg