M. Avoli et al., ELECTROPHYSIOLOGICAL AND REPETITIVE FIRING PROPERTIES OF NEURONS IN THE SUPERFICIAL MIDDLE LAYERS OF THE HUMAN NEOCORTEX MAINTAINED IN-VITRO, Experimental Brain Research, 98(1), 1994, pp. 135-144
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
.