Structural and functional specializations of human fast spiking neurons support fast cortical signaling

Fast synchronization frequencies are evolutionary conserved in the expanded human neocortex, despite larger neuron-to-neuron distances that challenge fast input-output transfer functions of FSINs. Here, we test in human neurons from neurosurgery tissue which mechanistic specializations of human FSINs explain their fast-signaling properties in human cortex.

With morphological reconstructions, multi-patch recordings, and biophysical modeling we find that despite three-fold longer dendritic path, human FSINs maintain fast inhibition between connected pyramidal neurons through several mechanisms: stronger synapse strength of excitatory inputs, larger dendrite diameter with reduced complexity, faster AP initiation, and faster and larger inhibitory output, while Na+ current activation/inactivation properties are similar.