Evidence for spike propagation in cortical dendrites

Abstract

A study was made of some of the properties of 99 spikes recorded from neurons scattered throughout the somatosensory cortex of the rat. All of the spikes were recorded extracellularly with microelectrodes, and were evoked by electrical stimulation of the skin of the contralateral forepaw. The behavior of every spike was followed over increasing cortical depths from the depth at which it was first recorded. Particular note was made of any changes in spike amplitude, spike latency, and spike frequency-following (i.e., the ability of the spike to follow repetitive peripheral stimulation of varying frequencies) that occurred concomitant with the changes in the cortical recording depth. The changes that were seen most often when the recording depth was increased were an increase in spike amplitude, a decrease in spike latency, and an increase in spike frequency-following. All these changes did not necessarily occur in the same spike. On six occasions the direction of these changes was reversed when the recording electrode was raised after having been lowered. One possible—and, it was thought, the most likely—interpretation of the results is that the recordings made were of spikes which were being actively propagated in ascending, vertically orientated, intracortical dendrites rather than in similarly orientated intracortical axons.