When a rose is not a rose: Pyramidal neurons respond differently in healthy and epileptic human neocortex

Epilepsy affects a huge number of patients by severe disruption of brain functions and is characterised by recurrent seizures, sometimes hard to be treated by medications. Seizure induced cellular consequences in ionic gradient and homeostasis are expected to result in electrophysiological differences between epileptic and non-epileptic neurons. In the following work, we demonstrate these differences in layer III cortical pyramidal neurons sourced from epileptic and non-epileptic human patient tissue. Although visually indistinguishable and featuring similar membrane potentials and latency to first spikes upon whole cell patch stimulation, epileptic pyramidal neurons display a larger rheobase and a smaller membrane resistance, responding less efficiently to electrical stimulation than their peri-tumorous equivalents. This decreased excitability contradicts results in comparable animal models of epilepsy and was further corroborated by detailed analysis of spiking characteristics and phase plot analysis of these events. Both point to an overexpression of K+ channels trying to compensate for the hyperexcited, epileptic network state. A computational model of a pyramidal neuron was utilized to give an estimate of the needful relative changes in K+ and Na+ conductances.