Beth Stevens: Learning by cutting connections?

Source: MacArthur Foundation

We are born with an excess of synaptic connections. Through a normal developmental process called “pruning”, some of those synaptic connections get cut. Which ones? How are synaptic connections selected for elimination? What does all of this mean for our theories of how linguistic patterns and structures are acquired by children? 

“Beth Stevens is a neuroscientist whose research on microglial cells is prompting a significant shift in thinking about neuron communication in the healthy brain and the origins of adult neurological diseases. Until recently, it was believed that the primary function of microglia was immunological; they protected the brain by reducing inflammation and removing foreign bodies.

Stevens identified an additional, yet critical, role: the microglia are responsible for the “pruning” or removal of synaptic cells during brain development. Synapses form the connections, or means of communication, between nerve cells, and these pathways are the basis for all functions or jobs the brain performs. Using a novel model system that allows direct visualization of synapse pruning at various stages of brain development, Stevens demonstrated that the microglia’s pruning depends on the level of activity of neural pathways. She identified immune proteins called complement that “tag” (or bind) excess synapses with an “eat me” signal in the healthy developing brain. Through a process of phagocytosis, the microglia engulf or “eat” the synapses identified for elimination. This pruning optimizes the brain’s synaptic arrangements, ensuring that it has the most efficient wiring.”

Related articles: Microglia: New Roles for the Synaptic Stripper (Neuron) and Phagocytic cells: sculpting synaptic circuits in the developing nervous system