Abstract
Numerous electrophysiology studies have shown the presence of mirror neurons throughout the macaque brain. Given that invasive human single cell data is scarcely available, the existence or absence of mirror neurons in the human brain has been inferred through indirect techniques like fMRI, where techniques like repetition suppression (RS) and multivariate pattern analysis (MVPA) have been suggested as tools to uncover the human mirror neuron system. Nevertheless, it has not been shown that MVPA analyses would suffice to reliably identify mirror neuron areas in the monkey. To investigate the potential of MVPA analyses to demonstrate common coding, we performed a comparative fMRI study in humans and macaques. Subjects either observed or executed reaching or grasping actions in a 3T scanner. Using both univariate and MVPA techniques, we investigated common coding for observed and executed actions at the whole brain level and in specific regions-of-interest. Our main focus was on investigating whether known monkey mirror neuron areas would allow successful cross-modal decoding. Univariate analyses yielded overlapping responses for observed and executed actions in parietal and frontal regions in both species. Unimodal decoding (separate for visual and motor domain) demonstrated action specificity in numerous brain regions, including visual, parietal, somatosensory, premotor and primary motor regions in humans and monkeys. Cross-modal decoding however, yielded asymmetric results in both species, showing significant decoding in a subset of regions only when going from visual to motor domain (training on visual, testing on motor data). Likewise, a region-of interest analysis of specific monkey brain regions known to house mirror neurons (F5, F1, AIP, PFG) only found unimodal or unidirectional cross-modal (visual to motor) evidence of action specificity and common coding. These data suggest that asymmetric cross-modal fMRI decoding results do not warrant strong claims about the presence of mirror neurons in the brain.
Meeting abstract presented at VSS 2016