Differential patterns of interhemispheric functional disconnection in mild and advanced multiple sclerosis

Area of Science:

• Neuroscience
• Neuroimmunology
• Motor Control

Background:

• Interhemispheric connectivity alterations are observed in multiple sclerosis (MS).
• Previous research focused mainly on primary motor cortex (M1) transcallosal connectivity in MS.
• Connectivity of non-primary motor areas remains less explored in MS.

Purpose of the Study:

• To investigate altered connectivity between the dorsal premotor cortex (dPMC) and contralateral M1 in MS patients.
• To determine if clinical progression exacerbates dPMC-M1 disconnectivity in MS.
• To differentiate effects on excitatory and inhibitory interhemispheric pathways.

Main Methods:

• Utilized a twin-coil transcranial magnetic stimulation (TMS) approach.
• Investigated excitatory and inhibitory interhemispheric connections between left dPMC and contralateral M1.
• Compared 18 MS patients without disability, 18 MS patients with advanced disease, and 12 healthy controls.

Main Results:

• Altered interhemispheric dPMC-M1 functional connectivity was found in MS patients, irrespective of clinical disability.
• Facilitatory dPMC-M1 connections were reduced in all MS patients.
• Inhibitory dPMC-M1 connections were altered only in MS patients with advanced disease.

Conclusions:

• Functional excitatory connectivity from non-primary motor areas is compromised in MS, even early in the disease.
• Clinical progression in MS leads to impairments in both excitatory and inhibitory transcallosal dPMC-M1 connections.
• Findings highlight the impact of MS on motor network connectivity beyond primary motor areas.