From Harvard Magazine:
Modern neuroscience rests on the assumption that our thoughts, feelings, perceptions, and behaviors emerge from electrical and chemical communication between brain cells: that whenever we recognize a face, read the newspaper, throw a ball, engage in a conversation, or recall a moment in childhood, a pattern of activity in our neurons makes such feats possible. It’s a tenet of modern biology that sparks fascination—and disbelief. How can a tangle of cells produce the complexity and subtlety of a mind?
Answering that question has always been propelled—and limited—by the available technologies. Accessing the living brain is difficult, and yet studying neurons outside their normal context can’t tell us how they work together normally. Today, using anatomical studies and technologies like functional magnetic resonance imaging, scientists can finally observe large-scale patterns of how the brain is organized. In animals, they have begun to map out networks of neurons responsible for processes like vision and smell. And detailed studies of individual neurons have revealed much about how they “fire” electrically in response to inputs from other neurons, or release neurotransmitters to communicate with one another. But one of the most difficult questions in neuroscience is how to connect these two scales: how do individual neurons link to one another in networks that somehow result in complex brain functions?