The human brain has an estimated 100 billion neurons. Extending from each of them is a long fiber, known as an “axon,” which can run several feet. Each axon forms a connection, known as a “synapse” with another neuron, creating a circuit over which brain signals travel.

In Alzheimer’s disease (AD), individual neurons die and do not regenerate. The loss of synapses correlates greatly with the loss of cognitive function.

Sometimes, if a circuit is too damaged to connect by the most direct route, signaling can take detours, leading to indirect neural pathways. It’s not until the network completely breaks down that the worst AD symptoms—like forgetting loved ones or becoming lost in familiar places—begin to occur.

Scientists are studying the brain’s many cells and circuits, looking for ways to preserve communications for as long as possible after the onset of AD.