Role of transcranial direct current stimulation (TDCS) intervention on resting state functional connectivity in early Alzheimer’s disease

Abstract

AbstractBackgroundWorking memory and executive function deficits are the characteristic features of Mild Cognitive Impairment and mild Alzheimer’s Disease (mild AD). Studies exploring the alterations in working memory and executive functions show disrupted functional connectivity in Dorsolateral Pre Frontal Cortices (DLPFC) and Angular Gyrus (AG). Transcranial direct current stimulation (tDCS), by stimulating these brain regions, can alter resting‐state functional connectivity (rs‐FC) and has emerged as a safe and non‐invasive technique that has the potential to enhance neuroplasticity and cognitive improvement.MethodWe investigated the effect of anodal stimulation at the left DLPFC and cathode placed at the right supra‐orbital area to observe the rsFC changes in patients with MCI and mild AD (n=12; Age=67.58 ± 8.59 years, Gender ratio 1:1, formal years of education= 14.58±3.55 years, Hindi mental Status examination=26.91±3.1), who attended the outpatient services of Geriatric Clinic and Services, after due approval from institute ethics committee NIMHANS. The resting‐state functional magnetic resonance imaging (rsfMRI) acquisitions were performed before and after the ten sessions of tDCS, each session lasting 20 minutes. Investigations were performed on subregions of DLPFC (left Superior Frontal Gyrus (LSFG), Right SFG, left Middle Frontal Gyrus (LMFG) and Right MFG) and Angular Gyrus (Right Angular Gyrus (RAG) and Left AG), chosen a priori as seeds for the seed based FC (sbFC) analysis after correcting for the influences of age and gender using CONN 18b toolbox. Spherical masks of size 5 mm diameter were also created for the above‐mentioned seeds.ResultThe pre‐post tDCS comparisons of sbFC showed significant (FDR; p<0.05) reduction of rsFC in patients with MCI and mild AD at right supramarginal gyrus, right angular gyrus, right frontal pole (for Seed‐RAG, Voxel‐ whole brain), supramarginal gyrus (for Seed‐RAG, Voxel‐ RAG), and Middle Temporal gyrus, left Temporo‐Occipital part (for Seed‐ RSFG, Voxel‐ whole brain) as shown in Figure 1 a, b, and c respectively (Refer Table 1).ConclusionThe results support that anodal stimulation using tDCS at left DLPFC may lead to the reduction of aberrantly increased functional connectivity between brain regions involved in working memory and executive functions in MCI and mild AD.