Thalamocortical sensorimotor circuit in multiple sclerosis: an integrated structural and electrophysiological...

Demyelination and axonal damage are pathologic hallmarks of multiple sclerosis (MS), leading to loss of neuronal synchronization, functional disconnection amongst brain relays, and clinical sequelae. To investigate these properties, the primary component of the sensorimotor network was analyzed in mildly disabled Relapsing-Remitting MS patients without sensory symptoms at the time of the investigation. By magnetoencephalography (MEG), the recruitment pattern within the primary sensory (S1) and motor (M1) areas was estimated through the morphology of the early components of somatosensory evoked magnetic fields (SEFs), after evaluating the S1 responsiveness to sensory inputs from the contralateral arm. In each hemisphere, network recruitment properties were correlated with ispilateral thalamus volume, estimated by morphometric techniques upon high-resolution 3D structural magnetic resonance images (MRI). S1 activation was preserved, whereas SEF morphology was strikingly distorted in MS patients, marking a disruption of primary somatosensory network patterning. An unbalance of S1-M1 dynamic recruitment was documented and correlated with the thalamic volume reduction in the left hemisphere. These findings support the model of MS as a disconnection syndrome, with major susceptibility to damage experienced by nodes belonging to more frequently recruited and highly specialized networks.