Biologists have long puzzled over why neurons have thousands of synapses. Now neuroscientists have shown they are crucial not just for recognizing patterns but for learning the sequence in which they appear.

Artificial intelligence is a field in the midst of rapid, exciting change. That’s largely because of an improved understanding of how neural networks work and the creation of vast databases to help train them. The result is machines that have suddenly become better at things like face and object recognition, tasks that humans have always held the upper hand in (see “Teaching Machines to Understand Us”). in.