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 i n the superficial/middle layers of human temporal neocortical slices o btained from patients undergoing neurosurgical procedures for the trea tment of epilepsy or brain tumour. In most of the neurons, inward memb rane rectification was observed when the cell was depolarized or hyper polarized from rest by intracellular injection of positive or negative current pulses. Bath application of tetrodotoxin abolished the depola rizing inward rectification, but not the ''anomalous rectification'' i n the hyperpolarizing direction. Single action potential firing was fo llowed by a fast afterhyperpolarization, a depolarizing afterpotential and a medium afterhyperpolarization, while a slower afterhyperpolariz ation was seen following repetitive firing. Blockade of Ca2+ channels with Cd2+ diminished all three types of afterhyperpolarization. Althou gh the repetitive firing pattern in all cells indicated that they disc harge in a regular-spiking fashion, 63% of the cells fired tonically i n the initial part of discharge, while the remaining 37% of the cells fired phasically. Frequency-current plot for the initial interspike in tervals during long depolarizing pulses revealed primary and secondary ranges of firing. Spike frequency adaptation was also observed. In co nclusion, our experiments indicate that human neocortical cells in the superficial/middle layers display electrophysiological characteristic s that are similar to those described in rodent and feline neocortices .