These observations have led to the concept that the two opposing synaptic conductances balance each other out and that this balance is important for proper cortical function. "Balance" is a useful concept as it qualitatively captures some important properties of excitation and inhibition in the cortex, like the overall proportionality mentioned above and the fact that manipulating one conductance without the other can shift cortical activity to un-physiological extremes. However it is also misleading if taken too literarily: first it should not be understood as excitatory and inhibitory conductances being equal, i.e. canceling each other out. Excitation and inhibition are differentially distributed along the soma, dendrites and axon initial segment of neurons and thus their exact ratio is highly dependent on where it is measured. Furthermore, the concept of balance may lead to the naive view that the main role of cortical inhibition is to prevent epileptiform activity, a notion that is clearly too simplistic. Finally, and most important, despite the overall proportionality of excitation and inhibition, their exact ratio is highly dynamic, as will be detailed below.
