Are there cortical somatotopic motor maps outside of the human precentral gyrus?

Abstract

Human body movements are supported by a somatotopic map, primary motor cortex (M1), that is found along the precentral gyrus. Recent evidence has suggested two further motor maps that span the lateral occipitotemporal cortex (LOTC) and the precuneus. Confirmation of these maps is important, as they influence our understanding of the organization of motor behavior, for example by revealing how visual- and motor-related activity interact. However, evidence for these recently proposed maps is limited. We analyzed an open functional MRI (fMRI) dataset of 62 participants who performed 12 different body part movements. We analyzed the magnitude of responses evoked by movements with novel quantitative indices that test for maplike organization. We found strong evidence for bilateral somatotopic maps in precentral and postcentral gyri. In LOTC, we found much weaker responses to movement and little evidence of somatotopy. In the precuneus, we found only limited evidence for somatotopy. We also adopted a background connectivity approach to examine correlations between M1, LOTC, and the precuneus in the residual time series data. This revealed a ventral-posterior/dorsal-anterior distinction in the connectivity between precuneus and M1, favoring the head and arms, respectively. Posterior right hemisphere LOTC showed some evidence of preferential connectivity to arm-selective regions of M1. Overall, our results do not support the existence of a somatotopic motor map in LOTC but provide some support for a coarse map in the precuneus, especially as revealed in connectivity patterns. These findings help clarify the organization of human motor representations beyond the precentral gyrus.NEW & NOTEWORTHY We investigated previous claims about the existence of somatotopic motor maps in the human lateral occipitotemporal cortex (LOTC) and the precuneus, in comparison to known maps in the precentral and postcentral gyri. Consistent with previous findings, we identified clear somatotopic motor maps in the latter two regions. With multiple quantitative measures of activity and connectivity, however, we found no evidence for a map in the LOTC and limited evidence for a map in the precuneus.