Causal contribution of motor-parietal network to conscious kinesthetic perception

Abstract

Bodily awareness, including the conscious experience of limb movements (kinesthesia), is a fundamental form of human consciousness. Tendon vibration–induced kinesthetic illusions provide a tractable model for probing its neural basis. Although the primary motor cortex (M1), right inferior parietal lobule (IPL), and right inferior frontal gyrus (IFG) are coactivated during illusory movement, whether and how the coordinated engagement of modality-specific motor and higher-order cortical regions causally contributes to conscious bodily experience remains unclear. Here, we combined functional magnetic resonance imaging (fMRI) and transcranial direct current stimulation (tDCS) to investigate the neural mechanisms and causal contribution of these regions to conscious kinesthetic perception. fMRI revealed that M1–IPL network supports kinesthetic illusions emerging through bottom-up sensory processing, whereas the IFG was selectively recruited when previously unnoticed kinesthetic signals became consciously experienced following knowledge, consistent with a role in top-down monitoring. Causal analysis further revealed a consistent bottom-up directional relationship from M1 to the IPL. To test its causal contribution, we applied concurrent facilitative dual-site tDCS to M1 and the IPL. M1–IPL tDCS selectively enhanced the subjective strength of the illusion compared with M1–IFG and sham stimulation. This effect was replicated in an independent cohort and exceeded the effects of stimulating M1 or the IPL alone and the IPL–IFG, without detectable muscle activation. These findings provide causal evidence that coordinated motor–parietal engagement contributes to conscious kinesthetic experience and provide new insights into how conscious sensory perception can be enhanced through interactions between modality-specific and higher-order cortical systems. Significance statement: Bodily awareness is fundamental to human consciousness, yet how cortical networks transform bodily signals into conscious experience remains unclear. Using tendon vibration-induced kinesthetic illusions, we combined functional magnetic resonance imaging (fMRI) and dual-site transcranial direct current stimulation (tDCS) to distinguish bottom-up from top-down processes and test their causal contributions. fMRI implicated the primary motor cortex (M1)–right inferior parietal lobule (IPL) network in bottom-up kinesthetic processing, whereas the right inferior frontal gyrus was selectively recruited during top-down monitoring. Concurrent M1–IPL tDCS robustly and reproducibly enhanced conscious kinesthetic perception without detectable muscle activation, exceeding other stimulation configurations. These findings provide causal evidence that coordinated motor–parietal engagement contributes to conscious bodily experience and advance mechanistic understanding of bodily awareness.