Causal contribution of motor-parietal network to conscious kinesthetic perception

Abstract

Bodily awareness, including the conscious experience of limb movement (kinesthesia), is a fundamental form of human consciousness. Tendon vibration-induced kinesthetic illusions provide a tractable model for probing its neural basis. Although previous studies have reported coactivation of the primary motor cortex (M1), the right inferior parietal lobule (IPL), and the right inferior frontal gyrus (IFG) during illusory movement, their causal contributions to conscious kinesthetic experience remain unclear. Here, we combined functional MRI and regional facilitative dual-site transcranial direct current stimulation (tDCS) to establish a causal link between these cortices and illusory foot movement. fMRI revealed that the M1-IPL network supports kinesthetic illusion elicited by bottom-up sensory processing, whereas the IFG plays a role in top-down monitoring of the kinesthetic experience. Critically, concurrent facilitative dual-site tDCS applied to the M1 and IPL significantly enhanced the subjective strength of the illusion, compared with the sham and concurrent tDCS to the M1 and IFG. This effect was replicated without increasing muscle activity in another tDCS study and exceeded those observed with single-site (M1 or IPL) or concurrent higher-order IPL-IFG tDCS. Our findings provide the first compelling causal evidence that conscious kinesthetic perception can be augmented through coordinated interactions between the modality-specific kinesthetic-motor cortex (M1) and the higher-order right inferior parietal cortex (IPL). This coordinated interaction between modality-specific and higher-order cortical regions underlying conscious kinesthetic perception is consistent with the Global Neuronal Workspace hypothesis. Our findings have therefore extended the applicability of this framework from exteroceptive perception to bodily awareness.