Electrophysiological and repetitive firing properties of neurons in the superficial/middle layers of the human neocortex maintained in vitro

Conventional intracellular recordings were made from neurons located in the superficial/middle layers of human temporal neocortical slices obtained from patients undergoing neurosurgical procedures for the treatment of epilepsy or brain tumour. In most of the neurons, inward membrane rectification was observed when the cell was depolarized or hyperpolarized from rest by intracellular injection of positive or negative current pulses. Bath application of tetrodotoxin abolished the depolarizing inward rectification, but not the “anomalous rectification” in the hyperpolarizing direction. Single action potential firing was followed by a fast afterhyperpolarization, a depolarizing afterpotential and a medium afterhyperpolarization, while a slower afterhyperpolarization was seen following repetitive firing. Blockade of Ca2 channels with Cd2 diminished all three types of afterhyperpolarization. Although the repetitive firing pattern in all cells indicated that they discharge in a regular-spiking fashion, 63% of the cells fired tonically in the initial part of discharge, while the remaining 37% of the cells fired phasically. Frequencycurrent plot for the initial interspike intervals during long depolarizing pulses revealed primary and secondary ranges of firing. Spike frequency adaptation was also observed. In conclusion, our experiments indicate that human neocortical cells in the superficial/middle layers display electrophysiological characteristics that are similar to those described in rodent and feline neocortices.