Language is embodied in the motor system – evidence from Metaanalysis

Embodiment links the individual sensorimotor experiences with higher cognitive functions such as language processing and comprehension. Connecting motor abilities with cognitive capacities contradicts with the classic view, which assumes a clear-cut separation between low and high level processes, and which states that cognition derives from computational processes in separate domains.

The embodiment perspective implies that brain areas related to action and language can no longer be seen as independent, but rather working in concert. Areas traditionally regarded as pure motor areas as e.g. the primary motor or the premotor cortex, as well as areas that have traditionally been assigned to the processing of language, e.g. Broca's or Wernicke's region, are not modularized, but rather provide the linkage of action and language.

The aim of our study was to review recent functional imaging literature on language and embodiment and to investigate the neural activity patterns across the incorporated studies. The meta-analysis follows a voxel based method comprising activation foci reported in the included studies.

An exhaustive literature search was conducted on studies indexed in the Medline database. We focused on fMRI studies, which contained the pre-specified keywords embodiment, language, motor, action, and perception. We included studies on words (verbs, nouns) and on sentences or both. Using Ginger ALE software provided by BrainMap [1] a statistical map was generated by using a collection of 365 foci from 15 studies. Each coordinate was modeled by a three-dimensional (3D) Gaussian function with 12mm FWHM. Thus, the localization probability distributions describe the probability that a given focus actually lay within a particular voxel.

Statistical significance is gained via a permutation test of randomly generated foci using the same FWHM and number of foci. The voxel-wise comparison is tested against the null-hypothesis of uniformly distributed peaks. Using the False Discovery Rate (FDR) with q=0.01, the test was corrected for multiple comparisons.

Major activity sites are displayed in the left hemisphere, predominantly in the frontal lobe, comprising the inferior frontal gyrus (BA 44, BA 46) and the precentral gyrus (BA 4, BA 6). In the parietal lobe, distinct clusters could be detected in the medial and supramarginal locations, as well as in the superior parietal lobulus and in the precuneus area. In the left temporal lobe, activations could be found in the middle temporal gyrus and more prominently in the fusiform area. Further findings include the insula in the left hemisphere as well as the bilateral cerebellum.

In summary, we support the idea that language is embodied. The meta-analysis on the current literature is able to demonstrate that the involvement of sensorimotor areas in language processing is far more than a mere by-product of task, subject selection or image processing, as one might assume from the analysis of a single task. The concluding meta-statement shows that motor abilities contribute to language comprehension, while language processing activates motor potentials. As a result, sensorimotor- and language systems work in concert to impact on action understanding.

Reference: [1] Laird A. R. et al.,. (2005). Hum Brain Mapp 25 (1), 155–164.