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Reference.org
Activating function
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<p>The activating function is a mathematical formalism that is used to approximate the influence of an extracellular field on an <a href="/facts/Axon/5DCd4wLo">axon</a> or <a href="/facts/Neuron/G7CyTVdH">neurons</a>. It was developed by Frank Rattay and is a useful tool to approximate the influence of <a href="/facts/Functional_electrical_stimulation/7UupxtsG">functional electrical stimulation (FES)</a> or <a href="/facts/Neuromodulation_(medicine)/2MHUQoBv">neuromodulation</a> techniques on target neurons. It points out locations of high <a href="/facts/Hyperpolarization_(biology)/XNH4zPwN">hyperpolarization</a> and <a href="/facts/Depolarization/qGX8lFXE">depolarization</a> caused by the electrical field acting upon the nerve fiber. As a rule of thumb, the activating function is proportional to the second-order spatial derivative of the extracellular potential along the axon. </p>