  Neuronal excitability is known to be affected by transcranial electrical
stimulation. However, due to the existence of both excitatory and inhibitory
neurons in the cortex, the mechanism of neuronal excitability shift is still
not clear. Here, we study electrical stimulation disturbance on neuronal
excitability in the neuromuscular system on an acute rat model. We design a
special stimulation waveform of enveloped high frequency stimulation (EHFS).
With modeling and in vivo measurements, EHFS is confirmed to synchronize the
neuronal recruitment at the positive and negative electrode. This unique
synchronization property of EHFS amplifies the electrical stimulation
disturbance on neuronal excitability, to enable the macroscopic observations of
large increase and decrease of force output. By eliminating the complicated
inhibitory interneuron effects in the cortex, our observations on the
neuromuscular system supports the argument that electrical stimulation
dynamically shifts neuronal excitability, by inducing depolarization during
anodal stimulation and hyperpolarization during cathodal stimulation.
