Fig. 2.
Active signal conduction along the apical dendrites of layer 5 cortical pyramidal neurons. (A) Corticocortical top–down projections contact primarily distal apical dendrites, and thus a very electrically remote region, of pyramidal neurons located in deeper layers of their target area. (B) However, top–down signals impinging upon even the most peripheral tuft dendrites can be carried actively toward the cell body by means of regenerative N-methyl-d-aspartate (NMDA) (green arrows) and calcium (blue arrow) potentials. Of note, action potentials triggered by stimulation to the neuron’s soma can back-propagate into the dendrite (black dotted arrow) and lower the threshold for dendritic calcium potentials.