From form to function: computational anatomy of dendritic spines and axonal branches

Cortical neurons present arborized dendritic and axonal trees. Essentially all the excitatory synaptic inputs are received in the dendritic spines, small neuronal appendages with diverse shapes. The output action potentials propagate along the axonal tree, through branching points, en-passant buttons, and terminal buttons. Here, we investigate the unique morphologies of these compartments and their effects on the activity pattern and communication between neurons.

Recent advancements in connectomics and new tools for in-vivo optical imaging of neuronal voltage enable a deeper exploration of the structure and function of dendritic and axonal segments. We developed new methods to computationally reconstruct spines and measure their heads and necks.

We found that dendritic spines, in cortical pyramidal neurons of mice and humans, have a continuum of morphologies and do not belong to distinct morphological subtypes. Overall, human cortical spines had longer and thicker necks and bigger head volumes than spines from the mouse cortex. In addition, we found human spines had longer and thinner necks in apical dendrites. These differences likely have functional meaning, as the neck causes biochemical and electrical isolation between the spine head and the dendritic shaft.