Abstract
Humans are vocal modulators par excellence. This ability is supported in part by the dual representation of the laryngeal muscles in the motor cortex. Movement, however, is not the product of motor cortex alone but of a broader motor network. This network consists of brain regions which contain somatotopic maps that parallel the organisation in motor cortex. We therefore present a novel hypothesis that the dual laryngeal representation is repeated throughout the broader motor network. In support of the hypothesis we review existing literature which demonstrates the existence of network-wide somatotopy, and present initial evidence for the hypothesis’ plausibility. Understanding how this uniquely human phenotype in motor cortex interacts with broader brain networks is an important step toward understanding how humans evolved the ability to speak. We further suggest that this system may provide a means to study how individual components of the nervous system evolved within the context of neuronal networks.
Highlights
This hypothesis is supported by the observations that (i) somatotopic maps throughout the motor network follow a similar ordering of representations from foot to face and (ii) nodes in the motor network project to one another homotopically, suggesting that motor regions beyond motor cortex must have target zones that receive the projections from the dLMC and vLMC
We have proposed a novel hypothesis that the dual representation of the laryngeal muscles found in the motor cortex is repeated throughout the motor network
Somatotopic organization is a feature that is found across the network of brain regions that control voluntary movement
Summary
More recent neurosurgical [16,17], molecular genetic [18] and brain imaging studies [19,20,21,22,23,24] provide compelling evidence that the laryngeal muscles are unusual in being controlled by two distinct loci within the human motor cortex. While other effectors such as the digits of the hand may have multiple representations in motor cortex, these tend to be contiguous and may represent either subdivision at a finer scale (i.e. muscles of flexion versus extension) or. We outline a novel hypothesis that this human phenotype is not restricted to the motor cortex but extends throughout a network of somatotopically arranged brain areas that comprise the motor system, including the cerebellum, SMA, BG and MCC and the axonal projections between these regions
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