Large-scale changes in cortical dynamics triggered by repetitive somatosensory electrical stimulation

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Biomedical Engineering

Background:

• Repetitive somatosensory electrical stimulation (SES) shows promise for improving motor function post-stroke.
• The direct neural modulation mechanisms of SES remain largely unknown.
• Previous SES studies primarily used noninvasive human methods.

Purpose of the Study:

• To investigate how SES directly impacts neural dynamics in the rodent primary motor cortex (M1).
• To assess changes at both single-neuron and mesoscale levels.
• To provide electrophysiological evidence of SES's direct cortical modulation.

Main Methods:

• Acute extracellular recordings in anesthetized rats (n=7) performing transcutaneous SES.
• Recorded single unit spiking and local field potentials (LFPs) in M1 contralateral to stimulation.
• Compared neural firing rate, spike-field coherence (SFC), and power spectral density (PSD) pre- and post-SES.

Main Results:

• A majority of M1 neurons exhibited significant changes in firing rate post-SES, with diverse increases and decreases.
• Spike-field coherence (SFC) significantly increased in the delta-band (0.3-4 Hz).
• The delta-band SFC increase was linked to phase-locking changes in broad-spiking neurons, without altering overall PSD.

Conclusions:

• Repetitive SES persistently alters local cortical dynamics in M1.
• SES modulates both individual neuron firing rates and their coupling to mesoscale oscillations (delta-band).
• This study provides direct electrophysiological evidence that SES modulates cortical dynamics.