10 Hz transcranial alternating current stimulation over posterior parietal cortex facilitates tactile temporal order judgment.

The temporal order judgment (TOJ) task has been widely used to investigate spatial attentional bias and the sensitivity of temporal discrimination during the processing of bilateral tactile information. Previous studies have shown that TOJ is impaired in patients who are suffering from chronic pain, stroke, and Parkinson's disease. In addition, studies have indicated that the posterior parietal cortex (PPC) is involved in the TOJ task. However, the neural basis of the TOJ task has not been fully elucidated. To investigate the causal relationship between cortical oscillation and certain behaviors, transcranial alternating current stimulation (tACS) has been used. tACS can entrain an oscillation in the cortex to the applying frequency. In previous studies, increased alpha-band (around 10 Hz) oscillation in the PPC is associated with attentional inhibition of the contralateral side. Therefore, we hypothesized that 10 Hz tACS over PPC would inhibit tactile processing in the contralateral side, leading to ipsilateral spatial attentional bias and impaired temporal discrimination. However, we found that 10 Hz tACS over either side of the PPC facilitated temporal discrimination, with 10 Hz tACS over the right PPC leading to a rightward shift of attentional bias. These findings indicated that 10 Hz tACS over the PPC has a facilitative effect in the processing of bilateral tactile information, and may be useful for modulating or treating spatial bias or temporal discrimination during the integration of bilateral stimulation, at least in the somatosensory domain.