Effects of Transcranial Direct Current Stimulation of the Posterior Parietal Cortex on Visual and Vestibular Function

Area of Science:

• Neuroscience
• Motor Control
• Brain Stimulation

Background:

• The effects of transcranial direct current stimulation (tDCS) on the posterior parietal cortex (PPC) regarding postural stability and cortical activity are not fully understood.
• The PPC plays a crucial role in integrating sensory information for motor control and maintaining balance.

Purpose of the Study:

• To investigate and compare changes in cortical activity and postural stability following different transcranial direct current stimulation (tDCS) polarities targeting the posterior parietal cortex (PPC).
• To determine the influence of bilateral tDCS over the PPC on postural control and associated cortical deactivation.

Main Methods:

• Eight healthy adults underwent three randomized transcranial direct current stimulation (tDCS) sessions targeting the posterior parietal cortex (PPC): left-anodal/right-cathodal, left-cathodal/right-anodal, and sham.
• Cortical activity was measured using functional near-infrared spectroscopy (fNIRS).
• Postural stability was assessed using the Balance Error Scoring System (BESS) and a force platform during a tandem stance.

Main Results:

• Left-cathodal/right-anodal (L-C/R-A) transcranial direct current stimulation (tDCS) over the posterior parietal cortex (PPC) resulted in significant deactivation in the right middle temporal gyrus (MTG) compared to baseline.
• The L-C/R-A condition led to significantly higher Balance Error Scoring System (BESS) scores and increased sway length compared to baseline and the left-anodal/right-cathodal (L-A/R-C) condition.
• These findings suggest a polarity-dependent effect of bilateral tDCS on postural control.

Conclusions:

• Bilateral transcranial direct current stimulation (tDCS) over the posterior parietal cortex (PPC) differentially affects cortical activity and postural control based on stimulation polarity.
• Left-cathodal/right-anodal (L-C/R-A) stimulation was associated with impaired visual-vestibular integration and reduced postural stability.
• Maintaining interhemispheric parietal balance is critical for posture regulation, and polarity-specific tDCS protocols may be important for future research and therapeutic applications.