Spine motility. Phenomenology, mechanisms, and function.

Throughout the history of neuroscience, dendritic spines have been considered stable structures, but in recent years, imaging techniques have revealed that spines are constantly changing shape. Spine motility is difficult to categorize, has different forms, and possibly even represents multiple phenomena. It is influenced by synaptic transmission, intracellular calcium, and a multitude of ions and other molecules. An actin-based cascade mediates this phenomenon, and while the precise signaling pathways are still unclear, the Rho family of GTPases could well be a "common denominator" controlling spine morphology. One role of spine motility might be to enable a searching function during synaptogenesis, allowing for more efficacious neuronal connectivity in the neuronal thicket. This idea revisits concepts originally formulated by Cajal, who proposed over a hundred years ago that spines might help to increase and modify synaptic connections.