Summary: Astrocytes, not microglia, are responsible for constantly eliminate unnecessary and excessive adult synaptic connections in response to brain activity.

Source: KAIST

Developing brains constantly sprout new neuronal connections called synapses as they learn and remember. Important connections — the ones that are repeatedly introduced, such as how to avoid danger — are nurtured and reinforced, while connections deemed unnecessary are pruned away. Adult brains undergo similar pruning, but it was unclear how or why synapses in the adult brain get eliminated.