Virtual Lesion Approach to Explain Linguistic Impairment in Multiple Sclerosis
Abstract
Introduction
Multiple sclerosis (MS) is an autoimmune maladaptive disease affecting the axons of the white matter; it causes the deterioration of the myelin sheet that insulates the axons in the nervous system [1]. Although physical or sensorimotor symptoms are the most common in MS, linguistic impairments are also observed. The language deficits may be of different kinds, affecting various abilities, for instance, verbal fluency, lexical access, or language comprehension [1].
Transient “virtual lesions” can be created with transcranial magnetic stimulation (TMS) through causing disruption of function and associated behaviour in a targeted cortical area [2]. This way, the causal role of areas can be tested, and virtual lesions can be used to simulate the effects of neurodegenerative diseases in the brain, such as the language alternations in MS.
Methods
The variety of linguistic symptoms suggests the complexity of the underlying cognitive processes. Thus, analysing language impairments in MS not only allows for insights into more general linguistic processes, but could improve treatment options by optimizing brain stimulation treatment designs. TMS-evoked virtual lesions allow for the non-invasive study of implications of neurodegenerative diseases in healthy subjects, without the involvement of actual patients. This aspect is important if the stage of neurodegeneration does not allow subjects to take part in the study, as people living with MS often experience fatigue, sensory deficits, or weakness [1].
The present study investigates the effect of TMS-induced virtual lesions on language processing in healthy subjects, in areas of the brain that are affected in MS. A picture naming task is used to focus on the most common linguistic symptom in MS: impairment of word retrieval [1]. The proposed project is relevant from a cognitive science perspective, as it analyses a complex cognitive phenomenon (language processing) and suggests possible applications and insights for medical treatment and diagnosis.
Expected Results
We aim to modify brain activity by using TMS for creating virtual lesions to alter language characteristics, allowing for translational insight into the linguistic processes in MS patients. Through localising – by probing different TMS coil positions – and analysing the speech-related altered behaviour, a more general brain–behavioural relationship may be derived and targeted therapeutic or rehabilitation methods for people living with MS may be found.
References
[1] S. Renauld, L. Mohamed-Saïd, and J. Macoir, “Language disorders in multiple sclerosis: A systematic review,” Multiple Sclerosis and Related Disorders, vol. 10, pp. 103–111, 2016.
[2] I. Weissman-Fogel and Y. Granovsky, “The ‘virtual lesion’ approach to transcranial magnetic stimulation: Studying the brain–behavioral relationships in experimental pain,” PAIN Reports, vol. 4, no. 4, 2019.
