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Multifocal Transcranial Direct Current Stimulation Modulates Resting-State Functional Connectivity in Older Adults Depending on the Induced Current Density.

ABSTRACT: Combining non-invasive brain stimulation (NIBS) with resting-state functional magnetic resonance imaging (rs-fMRI) is a promising approach to characterize and potentially optimize the brain networks subtending cognition that changes as a function of age. However, whether multifocal NIBS approaches are able to modulate rs-fMRI brain dynamics in aged populations, and if these NIBS-induced changes are consistent with the simulated electric current distribution on the brain remains largely unknown. In the present investigation, thirty-one cognitively healthy older adults underwent two different multifocal real transcranial direct current stimulation (tDCS) conditions (C1 and C2) and a sham condition in a crossover design during a rs-fMRI acquisition. The real tDCS conditions were designed to electrically induce two distinct complex neural patterns, either targeting generalized frontoparietal cortical overactivity (C1) or a detachment between the frontal areas and the posteromedial cortex (C2). Data revealed that the two tDCS conditions modulated rs-fMRI differently. C1 increased the coactivation of multiple functional couplings as compared to sham, while a smaller number of connections increased in C1 as compared to C2. At the group level, C1-induced changes were topographically consistent with the calculated electric current density distribution. At the individual level, the extent of tDCS-induced rs-fMRI modulation in C1 was related with the magnitude of the simulated electric current density estimates. These results highlight that multifocal tDCS procedures can effectively change rs-fMRI neural functioning in advancing age, being the induced modulation consistent with the spatial distribution of the simulated electric current on the brain. Moreover, our data supports that individually tailoring NIBS-based interventions grounded on subject-specific structural data might be crucial to increase tDCS potential in future studies amongst older adults.

SUBMITTER: Abellaneda-Perez K

PROVIDER: S-EPMC8662695 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:ObjectiveCathodal transcranial direct current stimulation (C-tDCS) is generally assumed to inhibit cortical excitability. The parietal cortex contributes to multisensory information processing in the postural control system, and this processing is proposed to be different between the right and left hemispheres and sensory modality. However, previous studies did not clarify whether the effects of unilateral C-tDCS of the parietal cortex on the postural control system differ depending on the hemisphere. We investigated the changes in static postural stability after unilateral C-tDCS of the parietal cortex.MethodsTen healthy right-handed participants were recruited for right- and left-hemisphere tDCS and sham stimulation, respectively. The cathodal electrode was placed on either the right or left parietal area, whereas the anodal electrode was placed over the contralateral orbit. tDCS was applied at 1.5 mA for 15 min. We evaluated static standing balance by measuring the sway path length (SPL), mediolateral sway path length (ML-SPL), anteroposterior sway path length (AP-SPL), sway area, and the SPL per unit area (L/A) after 15-minute C-tDCS under eyes open (EO) and closed (EC) conditions. To evaluate the effects of C-tDCS on pre- and post-offline trials, each parameter was compared using two-way repeated-measures analysis of variance (ANOVA) with factors of intervention and time. A post-hoc evaluation was performed using a paired t-test. The effect sizes were evaluated according to standardized size-effect indices of partial eta-squared (ηp2) and Cohen's d. The power analysis was calculated (1-β).ResultsA significant interaction was observed between intervention and time for SPL (F (2, 27) = 4.740, p = 0.017, ηp2 = 0.260), ML-SPL (F (2, 27) = 4.926, p = 0.015, ηp2 = 0.267), and sway area (F (2, 27) = 9.624, p = 0.001, ηp2 = 0.416) in the EO condition. C-tDCS over the right hemisphere significantly increased the SPL (p < 0.01, d = 0.51), ML-SPL (p < 0.01, d = 0.52), and sway area (p < 0.05, d = 0.83) in the EO condition. In contrast, C-tDCS over the left hemisphere significantly increased the L/A in both the EC and EO condition (EO; p < 0.05, d = 0.67, EC; p < 0.05, d = 0.57).ConclusionThese results suggest that the right parietal region contributes to static standing balance through chiefly visual information processing during the EO condition. On the other hand, L/A increase during EC and EO by tDCS over the left parietal region depends more on somatosensory information to maintain static standing balance during the EC condition.

Project description:Transcranial direct current stimulation (tDCS) over prefrontal cortex (PFC) regions is currently proposed as therapeutic intervention for major depression and other psychiatric disorders. The in-depth mechanistic understanding of this bipolar and non-focal stimulation technique is still incomplete. In a pilot study, we investigated the effects of bifrontal stimulation on brain metabolite levels and resting state connectivity under the cathode using multiparametric MRI techniques and computational tDCS modeling. Within a double-blind cross-over design, 20 subjects (12 women, 23.7 ± 2 years) were randomized to active tDCS with standard bifrontal montage with the anode over the left dorsolateral prefrontal cortex (DLPFC) and the cathode over the right DLPFC. Magnetic resonance spectroscopy (MRS) was acquired before, during, and after prefrontal tDCS to quantify glutamate (Glu), Glu + glutamine (Glx) and gamma aminobutyric acid (GABA) concentration in these areas. Resting-state functional connectivity MRI (rsfcMRI) was acquired before and after the stimulation. The individual distribution of tDCS induced electric fields (efields) within the MRS voxel was computationally modelled using SimNIBS 2.0. There were no significant changes of Glu, Glx and GABA levels across conditions but marked differences in the course of Glu levels between female and male participants were observed. Further investigation yielded a significantly stronger Glu reduction after active compared to sham stimulation in female participants, but not in male participants. For rsfcMRI neither significant changes nor correlations with MRS data were observed. Exploratory analyses of the effect of efield intensity distribution on Glu changes showed distinct effects in different efield groups. Our findings are limited by the small sample size, but correspond to previously published results of cathodal tDCS. Future studies should address gender and efield intensity as moderators of tDCS induced effects.

Project description:Introduction: Conventional transcranial direct current stimulation (tDCS) and high-definition tDCS (HD-tDCS) may improve motor learning in children. Mechanisms are not understood. Neuronavigated robotic transcranial magnetic stimulation (TMS) can produce individualised maps of primary motor cortex (M1) topography. We aimed to determine the effects of tDCS- and HD-tDCS-enhanced motor learning on motor maps. Methods: Typically developing children aged 12-18 years were randomised to right M1 anodal tDCS, HD-tDCS, or Sham during training of their left-hand on the Purdue Pegboard Task (PPT) over 5 days. Bilateral motor mapping was performed at baseline (pre), day 5 (post), and 6-weeks retention time (RT). Primary muscle was the first dorsal interosseous (FDI) with secondary muscles of abductor pollicis brevis (APB) and adductor digiti minimi (ADM). Primary mapping outcomes were volume (mm2/mV) and area (mm2). Secondary outcomes were centre of gravity (COG, mm) and hotspot magnitude (mV). Linear mixed-effects modelling was employed to investigate effects of time and stimulation type (tDCS, HD-tDCS, Sham) on motor map characteristics. Results: Twenty-four right-handed participants (median age 15.5 years, 52% female) completed the study with no serious adverse events or dropouts. Quality maps could not be obtained in two participants. No effect of time or group were observed on map area or volume. LFDI COG (mm) differed in the medial-lateral plane (x-axis) between tDCS and Sham (p = 0.038) from pre-to-post mapping sessions. Shifts in map COG were also observed for secondary left-hand muscles. Map metrics did not correlate with behavioural changes. Conclusion: Robotic TMS mapping can safely assess motor cortex neurophysiology in children undergoing motor learning and neuromodulation interventions. Large effects on map area and volume were not observed while changes in COG may occur. Larger controlled studies are required to understand the role of motor maps in interventional neuroplasticity in children.

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Multifocal Transcranial Direct Current Stimulation Modulates Resting-State Functional Connectivity in Older Adults Depending on the Induced Current Density.

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