Cellular effects of acute direct current stimulation: somatic and synaptic terminal effects

Area of Science:

• Neuroscience
• Computational Neuroscience
• Electrophysiology

Background:

• Transcranial direct current stimulation (tDCS) modulates cortical excitability, but the specific cellular compartments responsible for these changes are not fully understood.
• Existing models often assume radial current flow, potentially oversimplifying the complex cellular effects of tDCS.

Purpose of the Study:

• To investigate the acute effects of direct current stimulation (DCS) on excitatory synaptic efficacy.
• To determine which cellular compartments (somas, dendrites, axons, terminals) are the primary targets of tDCS-induced cortical excitability changes.
• To elucidate the role of current direction (radial vs. tangential) in modulating synaptic function.

Main Methods:

• Utilized multi-scale computational models of neuronal activity.
• Experimentally validated findings using rat cortical brain slices.
• Analyzed the direction and magnitude of current flow under typical tDCS montages.

Main Results:

• tDCS montages generate predominantly tangential currents, significantly exceeding radial currents.
• Radial currents modulate synaptic efficacy via somatic polarization, with depolarization enhancing it.
• Tangential currents modulate synaptic efficacy in an afferent pathway-specific manner via terminal polarization, with hyperpolarization enhancing it.
• Maximal polarization occurs at distal synaptic terminals, which are more susceptible than somata.

Conclusions:

• Both somata and axon terminals are critical cellular targets during acute tDCS.
• The direction of cortical current flow dictates the relative contribution of somata and terminals to synaptic efficacy modulation.
• Tangential currents play a significant role in tDCS effects, particularly at synaptic terminals.