Gyri-precise head model of transcranial direct current stimulation: Improved spatial focality using a ring electrode versus conventional rectangular pad

Abstract

The spatial resolution of conventional transcranial direct current stimulation (tDCS) is considered to be relatively diffuse owing to skull dispersion. However, here we show that electric fields may be clustered at distinct gyri/sulci sites due to details in tissue architecture/conductivity notably cerebrospinal fluid (CSF). We calculated the cortical electric field/current density magnitude induced during tDCS using a high spatial resolution (1 mm3) MRI-derived finite element human head model; cortical gyri/sulci were resolved. The spatial focality of conventional rectangular-pad (7 × 5 cm2) and the ring (4 × 1) electrode configurations were compared. The rectangular-pad configuration resulted in diffuse (un-focal) modulation, with discrete clusters of electric field magnitude maxima. Peak induced electric field magnitude was not observed directly underneath the pads, but at an intermediate lobe. The 4 × 1 ring resulted in enhanced spatial focality, with peak induced electric field magnitude at the sulcus and adjacent gyri directly underneath the active electrode. Cortical structures may be focally targeted using ring configurations. Anatomically accurate high resolution MRI-based forward-models may guide the ‘rational’ clinical design and optimization of tDCS.

Transcranial direct current stimulation may modulate extinction memory in posttraumatic stress disorder

“…However, these studies on tDCS after effects focused on the motor cortex, and as a result there is uncertainty about the direction of polarity after effects of prefrontal tDCS. The complexity of ultimate polarity effects of tDCS is in fact inherent to the nature of tDCS, in which current passes through all tissue in between the surface electrodes (Bikson et al., 2016; Philip et al., 2017), as demonstrated by electrical field modeling (Datta et al., 2009). …”

Impact of tDCS on performance and learning of target detection: Interaction with stimulus characteristics and experimental design

“…While we targeted the right frontal cortex, it is unlikely that tDCS resulted in focal stimulation of the brain, and may have included other brain regions as well. While there are no modeling studies that simulate the placement of the anode on the right frontal cortex with a cathode on the left upper arm, other studies indicate that even with two electrodes placed on the scalp the stimulation is diffuse and unpredictable (Datta et al, 2009;Miranda et al, 2009;Sadleir, Vannorsdall, Schretlen, & Gordon, 2010;Wagner, Valero-Cabre, & Pascual-Leone, 2007). Realistic, finite element head models suggest that a large fraction of the current passes into the brain via low resistance paths including the orbits and nose (Sadleir et al, 2010).…”

Neurostimulation as an intervention for treatment resistant depression: From research on mechanisms towards targeted neurocognitive strategies

“…Nonetheless, as concluded by several authors, its clinical utility remains unclear because there are not enough studies with large representative samples and optimized protocols to confirm the efficacy of tDCS (Brunoni, Ferrucci, Fregni, Boggio, & Priori, 2012;Kalu, Sexton, Loo, & Ebmeier, 2012), particularly for patients with TRD (Valiengo et al, 2013). Recently researchers are also experimenting with high density tDCS, which uses smaller electrodes to more precisely target specific brain areas (Datta et al, 2009). …”