Evidence for a motor somatotopy in the cerebellar dentate nucleus--an FMRI study in humans

Abstract

Previous anatomical studies in monkeys have shown that forelimb motor representation is located caudal to hindlimb representation within the dorso-rostral dentate nucleus. Here we investigate human dentate nucleus motor somatotopy by means of ultra-highfield (7 T) functional magnetic brain imaging (fMRI). Twenty five young healthy males participated in the study. Simple finger and foot movement tasks were performed to identify dentate nucleus motor areas. Recently developed normalization procedures for group analyses were used for the cerebellar cortex and the cerebellar dentate nucleus. Cortical activations were in good accordance with the known somatotopy of the human cerebellar cortex. Dentate nucleus activations following motor tasks were found in particular in the ipsilateral dorso-rostral nucleus. Activations were also present in other parts of the nucleus including the contralateral side, and there was some overlap between the body part representations. Within the ipsilateral dorso-rostral dentate, finger activations were located caudally compared to foot movement-related activations in fMRI group analysis. Likewise, the centre of gravity (COG) for the finger activation was more caudal than the COG of the foot activation across participants. A multivariate analysis of variance (MANOVA) on the x, y, and z coordinates of the COG indicated that this difference was significant (P = 0.043). These results indicate that in humans, the lower and upper limbs are arranged rostro-caudally in the dorsal aspect of the dentate nucleus, which is consistent with studies in non-human primates.

Figure 1

Cerebellar cortical activations following finger (red) and foot (blue) movement performed with the right side plotted on the SUIT template in coronal slices [Diedrichsen,2006], thresholded at P < 0.005 FDR corrected (threshold t value = 3.8, peak t value = 10). Lower row shows overlap between both conditions (threshold t value = 3.8, peak t value = 3.8). Color code denotes t values. White numbers indicate y‐coordinates. Latin numbers indicate cerebellar lobules. Right side of the image is right side of the brain. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Figure 2

Significant dentate nucleus activation following motor tasks plotted on probabilistic dentate nucleus template [Diedrichsen et al.,2011], shown in axial slices (white numbers indicate z‐coordinate). Finger movement related activation (left column) and foot related activation (middle column) are shown in red‐yellow. Color code denotes t values (threshold 3.79, peak 5). Overlay of both movement tasks (finger = red, foot = blue) is shown in the right column. For the right column, threshold and peak t value are both 3.79 for better delineation between tasks. Ipsi = ipsilateral side (right), Contra = contralateral side (left); r = rostral, c = caudal. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Figure 3

Dentate nucleus motor activation plotted on 3D surface reconstruction. Color code denotes t values. Ipsi = ipsilateral side (right), Contra = contralateral side (left). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]