Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation

Area of Science:

• Neuroscience
• Neurophysiology
• Neuromodulation

Background:

• Motor cortex excitability is crucial for motor control.
• Non-invasive methods to modulate brain activity are highly sought after.
• Previous methods for modulating brain excitability were often invasive or less precise.

Purpose of the Study:

• To investigate the feasibility of non-invasively modulating human motor cortex excitability.
• To determine the effects of weak direct current applied through the scalp.
• To explore the potential of transcranial electrical stimulation (TES) as a neuromodulatory tool.

Main Methods:

• Application of weak direct current (transcranial electrical stimulation - TES) to the scalp in intact human subjects.
• Assessment of motor cortex excitability using transcranial magnetic stimulation (TMS).
• Varied current intensity and duration to observe effects on excitability and after-effects.

Main Results:

• Demonstrated non-invasive modulation of motor cortex excitability by TES.
• Achieved excitability changes of up to 40%, lasting several minutes post-stimulation.
• Anodal stimulation increased excitability (excitation), while cathodal stimulation decreased it (inhibition).
• Current intensity and duration controlled the strength and duration of after-effects.

Conclusions:

• Weak transcranial electrical stimulation (TES) can effectively modulate human motor cortex excitability non-invasively.
• The observed effects are likely due to changes in membrane polarization and related neural plasticity mechanisms.
• TES offers a promising, painless, reversible, selective, and focal method for cerebral neuromodulation.