The Effect of Dual-Hemisphere Transcranial Direct Current Stimulation Over the Parietal Operculum on Tactile Orientation Discrimination

Abstract

The parietal operculum (PO) often shows ipsilateral activation during tactile object perception in neuroimaging experiments. However, the relative contribution of the PO to tactile judgment remains unclear. Here, we examined the effect of transcranial direct current stimulation (tDCS) over bilateral PO to test the relative contributions of the ipsilateral PO to tactile object processing. Ten healthy adults participated in this study, which had a double-blind, sham-controlled, cross-over design. Participants discriminated grating orientation during three tDCS and sham conditions. In the dual-hemisphere tDCS conditions, anodal and cathodal electrodes were placed over the left and right PO. In the uni-hemisphere tDCS condition, anodal and cathodal electrodes were applied over the left PO and contralateral orbit, respectively. In the tDCS and sham conditions, we applied 2 mA for 15 min and for 15 s, respectively. Computational models of electric fields (EFs) during tDCS indicated that the strongest electric fields were located in regions in and around the PO. Compared with the sham condition, dual-hemisphere tDCS improved the discrimination threshold of the index finger contralateral to the anodal electrode. Importantly, dual-hemisphere tDCS with the anodal electrode over the left PO yielded a decreased threshold in the right finger compared with the uni-hemisphere tDCS condition. These results suggest that the ipsilateral PO inhibits tactile processing of grating orientation, indicating interhemispheric inhibition (IHI) of the PO.

Dose response of somatosensory cortex repeated anodal transcranial direct current stimulation on vibrotactile detection: a randomized sham-controlled trial

“…This suggests an increased inhibition of sensory processing from the opposite side of the body in preference for efficient processing of sensory inputs on the tDCS stimulated side. Recent studies investigating unilateral and dual-hemisphere tDCS effects on the S1 and S2 further support this notion of opposite side interhemispheric inhibition of tactile processing (Fujimoto et al 2014(Fujimoto et al , 2017. With respect to sensory detection threshold levels, the mean detection thresholds obtained in this study for both high and low frequency vibrations were comparable to results reported by Morley and Rowe (1990) that had an identical VDT testing procedure.…”

“…The amplitude thresholds for detecting a 30Hz vibration are however much higher than for 200Hz, where the Pacinian channels could influence detection of the 30Hz stimuli since the threshold functions of different channels are quite close at this frequency (Gescheider et al 2002). Fujimoto et al (2017) however displayed through electric field monitoring of tDCS over the S2 with 25cm electrodes that a contributing stimulation of S1 could not be ruled out. It is therefore likely that our use of 35cm 2 electrodes over the S1 also contributed to stimulation of the S2 and possibly influencing both low and high frequency VDT processing.…”

“…To quantify any placebo effect there was a control group, which received sham stimulation only. This involved activating the tDCS device at a current intensity of 1mA but turning the tDCS device off slowly, out of the subject's field of view, after ~30 seconds (Gandiga et al 2006). The sham procedure chosen was based on research that demonstrated that ≤ two minutes of tDCS at a current intensity of .02857 mA/cm2 delivered to the motor cortex was insufficient to induce alterations post-stimulation to motor pathway excitability (Nitsche and Paulus 2000).…”

Transcranial Direct Current Stimulation on Parietal Operculum Contralateral to the Moving Limb Does Not Affect the Programming of Intra-Limb Anticipatory Postural Adjustments

“…First, it could be argued that tDCS duration and current intensity or density were insufficient for modulating PO excitability. This could be reasonably excluded, as Fujimoto et al (2017) obtained significant differences in tactile orientation discrimination when applying tDCS over PO, with the same current intensity but a 2.5 times smaller current density and for a duration 5-minute shorter than in our work. Moreover, if one takes into account the electric field simulations published by Fujimoto in the same paper, it is apparent that 2 mA tDCS is more than sufficient to alter the electric potential over the area of interest.…”

“…In this aim, we modulated coPO excitability by using anodal and cathodal transcranial Direct Current Stimulation (tDCS), a technique which has been proved to selectively interfere with the excitability of many cortical structures involved in motor and cognitive processes (for a review see Brunoni et al, 2013), including PO (Fujimoto et al, 2017). Notably, the applied currents are usually sufficiently low to grant a focal stimulation but nevertheless they produced long-lasting effects in many cases (Brunoni et al, 2013).…”