Waveforms and mechanisms in neuromodulation

All of neuromodulation is dependent on the delivery of a waveform comprised of electromagnetic fields to nervous system tissues in the human body. We are setting aside for now the types of neuromodulation working within the realm of light, ultrasonics, or any other forms of manipulating the function of a nervous system. Because the nervous system is generally thought to rely on information transfer to effect its processing of the external world and to make predictions for movement and behavior, and because that information appears to be carried in numbers and patterns of discrete ionic flux along axons from one location to another (referred to hereafter as action potentials or APs), it makes sense to try to intervene in that information transfer for therapeutic benefit when needed and where possible. Such interventions will necessarily be made with a certain frequency and pulse length and shape of pulse, as well as amplitude. These parameters are unavoidable. And so it is imperative that we understand how such variations in these basic parameters affect nervous tissue. A tremendous amount of knowledge has been generated along these lines and many textbooks cover much of this material (e.g., Ref. [1]) and we will not use this space to go into much of that detail in depth other than also to mention that an excellent summary of the physics and electrochemistry of that process is covered in this chapter. Here, we look at the shapes and cadence of the waveforms themselves and where they have been used already commercially, and then examine some aspects of how the waveforms may affect the actual mechanisms of action on the nervous tissue that we largely measure only on a behavioral level.