Region-Specific Effects of 10-Hz Transcranial Alternate Current Stimulation Over the Left Posterior Parietal Cortex and Primary Somatosensory Area on Tactile Two-Point Discrimination Threshold.

Hirotake Yokota,Yasuto Inukai,Hideaki Onishi,Shota Miyaguchi,Kei Saito,Kazuaki Nagasaka,Naofumi Otsuru,Sho Kojima

doi:10.3389/fnins.2021.576526

Hirotake Yokota, Yasuto Inukai + Show 6 more

Open Access

https://doi.org/10.3389/fnins.2021.576526

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Abstract

Changes in α-band cortical oscillatory activity (8–13 Hz) affect perception; however, how these changes in the left posterior parietal cortex (PPC) and primary somatosensory cortex (S1), which play different roles in determining the two-point discrimination (TPD) threshold, affect TPD threshold remains unelucidated. Therefore, to determine TPD threshold, we aimed to investigate the function of the left PPC and S1 by applying α-band transcranial alternating current stimulation (α-tACS; 10 Hz). TPD threshold was examined at the pad of the right index finger, contralateral to the stimulation site, in 17 healthy adults using a custom-made, computer-controlled, two-point tactile stimulation device, with random application of either active or sham α-tACS over the left PPC (Experiment 1) and left S1 (Experiment 2). Then, 50% TPD threshold was obtained in the active and sham conditions via logistic regression analysis. Afterward, we compared the difference between the active and sham conditions at 50% TPD threshold in each region and found that α-tACS reduced TPD threshold when applied over the left PPC (P = 0.010); however, its effect was insignificant when applied over the left S1 (P = 0.74). Moreover, a comparison of the change in 50% TPD threshold among the regions revealed that α-tACS applied over the left PPC significantly reduced TPD threshold compared with that applied over the left S1 (P = 0.003). Although we did not reveal the actual changes in cortical activity induced by α-tACS, this is the first empirical evidence that α-tACS applied over the left PPC and left S1 exerts region-specific effects on determining TPD threshold assessed in the contralateral index finger pad by stimulation.

Highlights

Haptic information from the outside world is input to areas 3b and 1 of the primary somatosensory cortex (S1) by ascending afferent fibers, such as the slowly adapting fibers and rapidly adapting fibers, and is sent to the secondary somatosensory cortex (S2) and higher-order areas, such as the posterior parietal cortex (PPC) (Inui et al, 2004)
The present study aimed to clarify the effects of non-invasive brain stimulation over the left PPC (Experiment 1) and left S1 (Experiment 2), which were suggested to be related to Two-point discrimination (TPD), on TPD threshold in the right index finger pad using 10-Hz α-band transcranial alternating current stimulation (α-Transcranial alternating current stimulation (tACS))
A comparison of the effects of α-tACS on the left PPC and left S1 based on the differences in 50% TPD threshold revealed that α-tACS applied over the left PPC significantly decreases TPD threshold compared with that applied over the left S1

Summary

Introduction

Haptic information from the outside world is input to areas 3b and 1 of the primary somatosensory cortex (S1) by ascending afferent fibers, such as the slowly adapting fibers and rapidly adapting fibers, and is sent to the secondary somatosensory cortex (S2) and higher-order areas, such as the posterior parietal cortex (PPC) (Inui et al, 2004). The inferior parietal lobule within the left PPC, a major region involved in attentional control (Corbetta et al, 2000; Yantis et al, 2002), is reportedly activated when performing a TPD task rather than during a simple sensory detection task (Sripati et al, 2006; Akatsuka et al, 2007, 2008; Pleger et al, 2016). Both S1 and PPC play important roles in the TPD process

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