Transcranial direct current stimulation effects on I-wave activity in humans

Area of Science:

• Neuroscience
• Neuromodulation
• Human Physiology

Background:

• Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique.
• tDCS exhibits polarity-specific effects on cortical excitability: anodal stimulation facilitates, while cathodal stimulation inhibits.
• Understanding the precise physiological mechanisms of tDCS is crucial for its therapeutic applications.

Purpose of the Study:

• To investigate the neurophysiological mechanisms underlying the polarity-specific effects of tDCS on human corticospinal excitability.
• To determine how anodal and cathodal tDCS influence intracortical circuits and corticospinal volleys.

Main Methods:

• Recording of corticospinal volleys evoked by single-pulse transcranial magnetic stimulation (TMS) in eight patients with epidural electrodes.
• Application of 5-minute anodal or cathodal tDCS to the primary motor cortex.
• Analysis of changes in motor evoked potential (MEP) amplitude and intracortical circuit excitability (I waves) before and after tDCS.

Main Results:

• Anodal tDCS enhanced the excitability of cortical circuits generating I waves, including the early I1 wave.
• Cathodal tDCS suppressed the excitability of later I waves.
• Changes in MEP amplitude correlated with the observed effects on intracortical circuitry.

Conclusions:

• tDCS induces polarity-specific changes in cortical excitability by modulating intracortical circuits.
• The findings provide further evidence for tDCS altering the excitability of cortical neurons.
• These results contribute to a deeper understanding of tDCS mechanisms for potential clinical use.