Transcranial magnetic and electrical stimulation compared: does TES activate intracortical neuronal circuits?

Area of Science:

• Neuroscience
• Motor Cortex Physiology
• Neuromodulation

Background:

• Transcranial electrical stimulation (TES) and transcranial magnetic stimulation (TMS) are non-invasive brain stimulation techniques.
• Understanding the precise neuronal structures activated by TES and TMS is crucial for their therapeutic applications.

Purpose of the Study:

• To compare the neuronal activation patterns of TES and TMS on the human motor cortex.
• To investigate the influence of current direction on motor cortex activation by TES and TMS.

Main Methods:

• Focal TMS and TES with varying electrode orientations (postero-anterior and latero-medial) were applied to three subjects.
• Electromyographic (EMG) recordings were used to analyze muscle response onset latencies and amplitudes.
• Paired-pulse paradigms assessed intracortical inhibition and excitation.

Main Results:

• TMS and TES with postero-anterior current direction yielded similar onset latencies.
• Latero-medial TES resulted in shorter onset latencies (1.4-1.9 ms).
• Paired-pulse TMS and TES (postero-anterior) induced both inhibition and facilitation, while latero-medial TES primarily caused facilitation.

Conclusions:

• Current direction is a critical determinant of neuronal activation for both TMS and TES.
• Postero-anterior stimulation likely activates corticospinal neurons indirectly, whereas latero-medial TES may directly activate corticospinal fibers.
• TES is effective for inducing intracortical inhibition and excitation, highlighting its potential in neuromodulation.