Electrokinesis hypothesis of neuron selection for synapse formation and pruning.

What neurons are connected and what neurons are disconnected? These are crucial questions since they determine the structural connectivity of the brain. We address this matter in question and propose a speculative hypothesis. We claim that the neuron selection for synapse formation and pruning process is an electrokinesis-based stochastic physical process. Propagating input signals generate a varying electromagnetic field in the interstitial fluid, which is filled with ions. Varying electromagnetic field exerts Lorentz force on the ions and causes local fluid flows. These fluid flows alter the position of presynaptic boutons and dendritic spines, and hence the likelihood of making contact. Above a certain level of field strength, the likelihood of pruning increases. If the proposed hypothesis is correct, in addition to explaining the natural process of neuron selection for synapse formation and pruning, it can also explain why and why not brain stimulation techniques work. Additionally, it will provide a controllable mechanism to alter brain connectivity as desired, which may have a profound impact on many connectivity-based psychiatric and neurological diseases.