Motor imagery enhances swallowing motor cortex excitability and activates sensorimotor regions: a TMS and fNIRS study

Action observation (AO) and motor imagery (MI) represent promising, non-invasive strategies for promoting neuroplasticity in motor rehabilitation by engaging the shared neural substrates of actual movement. However, their translation to swallowing rehabilitation, particularly for neurogenic dysphagia, lacks a robust neurophysiological foundation. A critical barrier is the absence of direct, multimodal evidence comparing how swallowing-specific static AO (SAO), dynamic AO (DAO), and MI differentially engage the cortical swallowing network. Specifically, their immediate effects on corticobulbar excitability and hemodynamic activation within key sensorimotor regions remain unquantified and poorly contrasted, limiting the rationale for their targeted clinical application. This study employed a dual-modal neuroimaging approach to precisely quantify and compare the immediate neurophysiological effects of SAO, DAO, and MI on the human swallowing sensorimotor system. We aim to evaluate their modulatory effects on bilateral suprahyoid motor cortical excitability and intracortical inhibitory/facilitatory circuitry using transcranial magnetic stimulation (TMS), and map their hemodynamic activation patterns within core sensorimotor cortices compared to motor execution (ME) using functional near-infrared spectroscopy (fNIRS). Thirty-two healthy adults underwent integrated assessments using transcranial magnetic stimulation (TMS) and functional near-infrared spectroscopy (fNIRS). TMS measured motor-evoked potentials (MEPs), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) in bilateral suprahyoid motor cortices during rest, SAO, DAO, and MI. fNIRS mapped hemodynamic changes in dorsal/ventral precentral (dPreCG/vPreCG) and postcentral gyri (dPoCG/vPoCG), superior/middle frontal gyri (SFG/MFG) during swallowing-specific SAO, DAO, MI and ME. MI reduced bilateral SICI and increased left ICF, concurrently activating bilateral dPoCG, left SFG/MFG, and right dPreCG/vPreCG/vPoCG—regions overlapping with ME-activated networks (bilateral vPreCG/vPoCG/MFG), with left MFG, right vPreCG/vPoCG as coactivating areas. In contrast, DAO reduced left SICI but elicited no hemodynamic activation, while SAO showed no significant effects. MI enhances the excitability of the swallowing motor cortex and activates the key sensorimotor cortical areas governed ME of swallowing. MI shows greater superiority over AO and may become a promising effective rehabilitation strategy for neurogenic dysphagia. Trial registration Chinese Clinical Trial Registry, ChiCTR2000036715. Registered on 24 August 2020, https//www.chictr.org.cn/bin/home.