MODELLING OF EFFECTIVE CONNECTIVITY OF MOTOR REGIONS IN BRAIN USING DYNAMIC CAUSAL MODELLING (DCM)

Abstract

Brain mapping is very topical issue these days. The insights into the neural coupling underlying a task between regions provides an understanding of brain functions and comparing this normal coupling with diseased brain provides a way to propose a better diagnosis and treatment strategies. There has been extensive work on functional and effective with reference to the cotical control of the upper limbs and lower limbs but to date, there was no study investigating underlying dynamics of tongue movement via effective connectivity. The objective of this study was to investigate underlying motor network dynamics of tongue movements as tongue is being extensively used for important functions in daily life e.g. swallowing, mastication, speech etc. Many disorders e.g. dysphagia, dysarthria are associated with impaired tongue function. We aimed to explore the role of premotor regions in control of tongue movement. We also aimed to investigate the influence of motor regions of limbs onto the tongue morot regions underlying movement of tongue. For this, fMRI data was acquired from human connectome project (HCP) database for a motor task involving movements of upper limbs, lower limbs and tongue. 17 subjects were considered for analysis. Our study included 10 regions of interest consisting of right and left motor representations of hands, feet and tongue along with the right and left hemispheric representations of supplementary motor area and premotor cortex (M1HL, M1HR, M1FL, M1FR, M1TL, M1TR, SMAL, SMAR, vPMCL and vPMCR). The approach used was dynamic causal modelling ( DCM) for inerring effective connectivity and novel post hoc Bayesian procedures i.e. PEB and BMR for group analysis which provide us more accurate, efficient, computationally inexpensive and quick way to make inferences on group level in contrast to standard Bayesian procedures. Our results provide us interesting insights into the control of tongue movement e.g. both contralateral and ipsilateral connections play role in control of tongue movement and motor regions of the hands and feet do not influence activity of the tongue motor regions. These findings provide useful information regarding control of tongue movement by motor cortex.