Abstract:
The purpose of this study was to investigate the interaction of the neural couplings underlying tongue movements with the movements of the hands and feet. We intend to explore whether the movement of the tongue differentially facilitates any of the upper or lower limb movements, since upper limbs are more frequently used in daily life. We examined the neural modulation of the motor network in 20 healthy subjects while they performed the motor task. The fMRI data of the motor task was downloaded from the human connectome project (HCP) database (https://db.humanconnectome.org/app/template/Login.vm). The motor task consisted of finger tapping, foot squeezing and horizontal and vertical movements of the tongue. Our study included 8 regions of interest consisting of right and left motor representations of the hands, feet and tongue along with the right and left hemispheric representations of the supplementary motor area (M1HL, M1HR, M1FL, M1FR, M1TL, M1TR, SMAL and SMAR). We used functional connectivity analysis and dynamic causal modeling to investigate the modulatory influence of regions of the tongue, hands and feet onto each other while the participants perform the tongue movements. The connectivity analysis showed that the M1 representations of hands and feet received strong inhibitory input from bilateral SMA during tongue movements. Furthermore, M1TL received strong excitatory input from both the contralateral and ipsilateral SMA, while M1TR received inhibitory input from contralateral while excitatory input from Ipsilateral SMA. Also, the backward connections from M1TL to SMA were excitatory while M1TR exerts inhibitory influence onto both the SMA. Moreover, the self-connections of M1TR were strongly inhibited while the self-connections of M1TL were excitatory. Our results indicate differential activation profiles of M1TL and M1TR, suggesting the motor control of the tongue are to be left
lateralized. Our effective connectivity results are consistent with the previous fMRI studies reporting lateralization of tongue movement.
