A computational study on effect of a transcranial channel as a skull/brain interface in the conventional rectangular patch-type transcranial direct current stimulation.

A conceptual model of a transcranial channel was recently proposed for conveying external currents of the skull to the brain; the effects of the transcranial channel combined with high-definition transcranial direct current stimulation (HD-tDCS) was investigated, resulting in discovery of increased stimulus intensity and focality. In this work, rather than HD-tDCS using smaller disc-type electrodes, we proposed the use of the transcranial channel with conventional tDCS using larger patch electrodes. We used multi-scale computational models that couple an anatomically realistic head model with multi-compartmental models of cortical neurons. We then predicted the excitability in the hand knob (target area) based on stimulus-induced electric fields and steady-state membrane polarizations. Conventional tDCS without the transcranial channel resulted in diffuse distributions of electric fields that covered the frontal cortex, while the spatial focality and intensity of the excitability increased significantly at the target area in the presence of the transcranial channel. Thus, it is expected that conventional tDCS with the transcranial channel allows a better targeting neuromodulation with higher intensity and may be promising for applying prolonged and stabilized tDCS.

Recent advances in biomagnetism and its applications

No abstract available.

Effects of electrode displacement in high-definition transcranial direct current stimulation: A computational study.

In order to understand better the ways in which cortical excitability is linked to target brain areas, this study describes the effects of focalized high-definition transcranial direct current stimulation (HD-tDCS), and investigates the way in which these effects persisted after the stimulus electrodes were displaced from the target area. We constructed a 3D volume conduction model of an anatomically realistic head that is ideal for HD-tDCS, as well as compartmental models of layer 3 and layer 5 pyramidal neurons. Using extracellular approaches, we observed stimulus-induced electric fields and simulated neuronal responses by combining stimulus-induced potential fields with pyramidal neuronal models coupled with the head model. We found that the stimulus-induced electric fields were focused on the hand-knob when the electrodes were placed directly above the target region; further, the neuronal responses varied, such that the upper parts of the dendrites were hyperpolarized, while the soma and axons were depolarized. The magnitude of the electric fields, as well as the maximum polarizations at each compartment decreased according to the displacement of the electrodes from the target area. Considerable excitability at the target area within the range of 5 mm displacement between electrodes and the target area was shown by means of stimulus-induced electric fields and membrane polarization. In conclusion, using detailed computational approaches, we discovered the ways in which excitability in the target area persisted even with increased distance from the active electrode.

Oscillatory brain activity changes by anodal tDCS - An ECoG study on anesthetized beagles.

Measuring neuronal activity of transcranial direct current stimulation (tDCS) is essential for investigating tDCS in stimuli or after stimuli effects. The aim of this study was to investigate the oscillatory changes from anodal tDCS using electrocorticography (ECoG) on beagles. We applied 2 mA anodal tDCS and monitored the ECoG signals (32 channels, 512 Hz sampling rate) for 15 minutes in three anesthetized beagles. Then, we compared the power changes before, during, and after tDCS in six different bands (delta, theta, alpha, beta, low-gamma, and mid-gamma bands). The significantly increasing oscillatory changes from the mid-frequency bands (theta, alpha, and beta bands) to the high-frequency bands (low-gamma and mid-gamma bands) were observed. The results suggest that anodal tDCS may modulate high-frequency bands in the focal area of the cortex, which is relevant to electroencephalogram (EEG) studies.