Accelerated signal propagation speed in human neocortical dendrites

Area of Science:

• Neuroscience
• Computational Neuroscience
• Cellular Neuroscience

Background:

• Human cognitive abilities rely on cerebral cortex information processing.
• Human cortical neurons are larger, with longer and sparser processes than rodent neurons.

Purpose of the Study:

• To investigate how signal propagation speed is maintained in larger human cortical neurons.
• To identify the biophysical mechanisms underlying faster signal transmission in human neurons.

Main Methods:

• Synaptically connected layer 2/3 pyramidal cells (L2/3 PCs) were studied in humans and rodents.
• Axonal and dendritic recordings were performed to measure signal propagation speeds.
• Experimentally-based biophysical models were used to analyze contributing factors.

Main Results:

• Soma-to-soma signal propagation delay is similar in human and rodent L2/3 PCs.
• Action potential propagation speed is comparable in human and rat axons.
• Excitatory postsynaptic potential (EPSP) forward propagation and action potential (AP) backward propagation are significantly faster in human dendrites.

Conclusions:

• The large conductance load from the basal dendritic tree at the soma is a key factor in accelerated EPSP propagation in human dendrites.
• Larger dendritic diameters and distinct cable/ion channel properties also enhance signal propagation in humans.
• These findings offer insights into neural scaling rules that preserve information processing speed in the human cortex despite larger neuron size.