DIFFERENCES IN SIGNAL PROPAGATION VELOCITY BETWEEN HUMAN AND RAT PYRAMIDAL CELL DENDRITES
The human cerebral cortex is the site of human-specific cognitive abilities. Pyramidal cells in the human cortex are larger compared to rats, however the temporal resolution of cortical microcircuits appear to be similar in these two species. Accordingly, modeling studies predict that information must travel faster in human microcircuits, but direct experimental evidence is lacking. We investigated signal propagation velocity in dendrites of human and rat pyramidal cells using simultaneous recordings of synaptically connected pyramidal cell pairs and dual somatic and dendritic whole cell measurements. Lengths of dendritic paths between putative synapses to the soma were determined on post-hoc reconstructions of the cell pairs. Synaptic latencies in human versus rat pyramid to pyramid cell pairs were similar in the two species (1.138±0.43 vs. 1.46±0.4 ms, respectively), however, averages of dendritic path lengths were different (human: 117.57±50.73 vs. rat: 90.12±42.34 μm). Direct measurements of signal propagation velocity between somatically and dendritically placed electrodes confirmed faster propagation of action potentials in human pyramidal cells (human, 0.544±0.19 m/s; rat, 0.363±0.08 m/s; p=0.0017). In conclusion, human pyramidal cells effectively compensate for larger dendritic signal routes by increasing propagation speed. Mechanisms underlying the elevated dendritic propagation speed in human cell still need to be further investigated.