Evaluation of the effect of transcranial direct current stimulation on language impairments in the behavioural variant of frontotemporal dementia

Clara Sanches; Fanny Amzallag; Bruno Dubois; Richard Lévy; Dennis Q Truong; Marom Bikson; Marc Teichmann; Antoni Valero-Cabré

doi:10.1093/braincomms/fcac050

Evaluation of the effect of transcranial direct current stimulation on language impairments in the behavioural variant of frontotemporal dementia

Brain Commun. 2022 Mar 29;4(2):fcac050. doi: 10.1093/braincomms/fcac050. eCollection 2022.

Authors

Clara Sanches¹, Fanny Amzallag¹, Bruno Dubois^{1

2}, Richard Lévy^{1

2}, Dennis Q Truong³, Marom Bikson³, Marc Teichmann^{1

2}, Antoni Valero-Cabré^{1

4

5}

Affiliations

¹ Groupe de Dynamiques Cérébrales, Plasticité et Rééducation, FRONTLAB team, Institut du Cerveau et de la Moelle Epinière, CNRS UMR 7225, INSERM 1127, Sorbonne Université, Paris, France.
² Department of Neurology, National Reference Center for « PPA and rare dementias », Pitié Salpêtrière Hospital, AP-HP, Paris, France.
³ Neural Engineering Laboratory, Department of Biomedical Engineering, The City College of City University of New York, New York, NY, USA.
⁴ Laboratory for Cerebral Dynamics Plasticity and Rehabilitation, Boston University School of Medicine, Boston, MA, USA.
⁵ Cognitive Neuroscience and Information Technology Research Program, Open University of Catalonia (UOC), Barcelona, Spain.

Abstract

The behavioural variant of frontotemporal dementia is a neurodegenerative disease characterized by bilateral atrophy of the prefrontal cortex, gradual deterioration of behavioural and executive capacities, a breakdown of language initiation and impaired search mechanisms in the lexicon. To date, only a few studies have analysed the modulation of language deficits in the behavioural variant of frontotemporal dementia patients with transcranial direct current stimulation, yet with inconsistent results. Our goal was to assess the impact on language performance of a single session of transcranial direct current stimulation on patients with the behavioural variant of frontotemporal dementia. Using a sham-controlled double-blind crossover design in a cohort of behavioural frontotemporal dementia patients (n = 12), we explored the impact on language performance of a single transcranial direct current stimulation session delivering anodal or cathodal transcranial direct current stimulation, over the left and right dorsolateral prefrontal cortex, compared with sham stimulation. A Letter fluency and a Picture naming task were performed prior and following transcranial direct current stimulation, to assess modulatory effects on language. Behavioural frontotemporal dementia patients were impaired in all evaluation tasks at baseline compared with healthy controls. Computational finite element method (FEM) models of cortical field distribution corroborated expected impacts of left-anodal and right-cathodal transcranial direct current stimulation over the dorsolateral prefrontal cortex and showed lower radial field strength in case of atrophy. However, none of the two tasks showed statistically significant evidence of language improvement caused by active transcranial direct current stimulation compared with sham. Our findings do not argue in favour of pre-therapeutic effects and suggest that stimulation strategies evaluating the modulatory role of transcranial direct current stimulation in the behavioural variant of frontotemporal dementia must carefully weigh the influence of symptom severity and cortical atrophy affecting prefrontal regions to ensure clinical success.

Keywords: frontotemporal dementia; language impairment; neurodegenerative diseases; non-invasive neuromodulation; transcranial direct current stimulation.