In the human brain, some 86 billion neurons form 100 trillion connections to each other - numbers that, ironically, are far too large for the human brain to fathom.

This image is misleading: Neurons don’t exist in isolation. Many of us have seen microscopic images of neurons in the brain - each neuron appearing as a glowing cell in a vast sea of blackness. Harvard COVID-19 Information: Keep Harvard Healthy.Research Departments, Centers, Initiatives and more.