  Measurements of electric potentials from neural activity have played a key
role in neuroscience for almost a century, and simulations of neural activity
is an important tool for understanding such measurements. Volume conductor (VC)
theory is used to compute extracellular electric potentials such as
extracellular spikes, MUA, LFP, ECoG and EEG surrounding neurons, and also
inversely, to reconstruct neuronal current source distributions from recorded
potentials through current source density methods. In this book chapter, we
show how VC theory can be derived from a detailed electrodiffusive theory for
ion concentration dynamics in the extracellular medium, and show what
assumptions that must be introduced to get the VC theory on the simplified form
that is commonly used by neuroscientists. Furthermore, we provide examples of
how the theory is applied to compute spikes, LFP signals and EEG signals
generated by neurons and neuronal populations.
