Function directs form of neuronal architecture

The human brain is an architectural marvel. The structure of each brain neuron and the interconnected networks they create are critical to all brain functions, and structural abnormalities are directly associated with neurological disorders. Although the human genome encodes only a few tens of thousands of genes, the human brain is estimated to be composed of hundreds of billions of neurons connected by trillions of synapses. Each brain neuron has an elaborate morphology critical to its functions of collecting, processing and disseminating information. Brain neurons are typically polar cells, composed of a tree-like dendritic arbor that receives and integrates synaptic input from upstream sources, a cell body, and an output axonal process and arbor that terminate locally or distantly to transmit signals to downstream targets. Although their morphologies follow neuronal-type basic patterns, each neuron is unique in number and position of axonal and dendritic branches and the constellation of pre- and postsynaptic cells contacted. Deciphering how such complex cell morphologies and networks form is a leading question in developmental neuroscience, central to understanding the origins of numerous common neurodevelopmental disorders, such as Autism Spectrum Disorders, schizophrenia and epilepsy. Recent research has begun to unravel this mystery, revealing that the structure of complex neural systems can emerge through self-organization following rules based on use-dependent testing of synapses and their stabilization of dynamically growing neuronal processes.