Thalamocortical sensorimotor circuit in multiple sclerosis: An integrated structural and electrophysiological assessment

Abstract

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.

Cortico-muscular coherence as an index of fatigue in multiple sclerosis

“…condition of continuous request of movement over-correction induced by an altered sensory feedback. 14 We derived from healthy people the expectation of higher CMC amplitude, but our MS patients showed CMC higher in frequency, not in amplitude. In particular, CMC amplitude in MS patients was similar to findings already published in a population of young adults executing the same task (.08 ± .04, 10 subjects with age range 21-35 years).…”

Inter-hemispheric functional connectivity changes with corpus callosum morphology in multiple sclerosis

“…Moreover, movement-related inter-hemispheric connectivity did not show any relationship with thalamic atrophy, suggesting a minor role of indirect fibers originating from thalamic nuclei (Dell'Acqua et al, 2010). …”

Functional role of ipsilateral motor areas in multiple sclerosis

“…In contrast to stroke with typically one acute ischaemic brain lesion, MS is a chronic neurological disease that is characterised by both demyelination and axonal injury occurring widely across the CNS1–3 and accumulating over time. As a result, both intra- and interregional structural cortical networks lose their topological efficiency and are disconnected progressively 4. In view of this chronic and global challenge by MS, it is conceivable that compensatory mechanisms differ between MS and stroke, an issue of great clinical interest with regard to potentially differential rehabilitation efforts.…”