Discovering the somatotopic organization of the motor areas of the medial wall using low‐frequency bold fluctuations

Abstract

bstract: This study explored the somatotopy of the motor areas of the medial wall of the cerebral hemisphere, in the human brain. In a sample of 16 healthy participants, we drew 9 regions of interest (ROI) over the primary motor area (M l), each corresponding to a well-known somatic representation. Using functional magnetic resonance imaging, we investigated the resting state functional connectivity between each selected ROI and the motor areas of the medial wall. The main finding was the identifi cation of a rostrocaudal gradient of connectivity in which the more we move from cranial to caudal body representation areas in M l, the more the corresponding connected area in the medial wall is shifted rostrocaudally, confirming the somatotopic schema found in the SMA. We also reanalyzed data obtained in a previous experiment, we performed using hand and foot motor tasks; the reanalysis con sisted in traditional BOLD and functional connectivity analyses. Finally, we performed a meta-analysis of 28 studies of hand and foot motor tasks, mapping their cerebral representations using the tools pro vided by the Brainmap database. All data converge in confirming a somatotopic representation of the medial wall motor areas, with hand representation placed more rostrally and ventrally than that of the foot. Hum Brain Mapp 32:1566Mapp 32: -1579Mapp 32: , 2011 e 2010 W iiey-Liss, inc.Keywords: motor areas; medial wall; supplementary motor area; SMA; cingulate motor areas; resting state; functional connectivity; seed voxel correlation; functional magnetic resonance imaging; fMRI; somatotopy IN T R O D U C T IO NEver since they were first identified, the motor areas of the medial wall have remained, in large part, a mystery. Originally the only recognized motor area in the mesial face of the brain was the supplementary motor area (SMA), located in the medial portion of Brodmann's cytoarchitectonic area 6 [Penfield and Welch, 1951; Woolsey et al., 1952]. This knowledge was derived through electrical stimulation of the cortical surface of the human brain during surgery for brain tumors. We now know of five premotor areas, located in subfields of Brod mann's areas 6, 23, and 24. These premotor areas include the SMA, the pre-SMA [Rizzolatti et a l, 1996;Tanji 1996], and three areas located within the cingulate sulcus-the rostral, dorsal, and ventral cingulate motor areas (CMAr, CM Ad, and CMAv, respectively). The SMA and pre-SMA are located in the dorsomedial frontal cortex, rostrally to the leg representation of the primary motor cortex (M l). The SMA is located caudal to the vertical projection of the commissure, while the pre-SMA lies rostral to this line. The three cingulate motor areas are located within the homonym sulcus: the CMAr and CMAv in the ventral bank of the sulcus and the CMAd in the dorsal bank; each cingulate motor area corresponds to a different cytoarchitectonic field.The somatotopic organization of the motor areas of the medial wall was originally studied in nonhuman primates by observing movements evoked by int...

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