In our brains, where millions of signals move across a network of neurons like runners in a relay race, all the critical baton passes take place at synapses. These small gaps between nerve cell endings have to be just the right size for messages to transmit properly. Synapses that grow too large or too small are associated with motor and cognitive impairment, learning and memory difficulties, and other neurological disorders.

Your ability to listen to a phone message in one ear while a friend is talking into your other ear—and comprehend what both are saying—is an important communication skill that’s heavily influenced by your genes, say researchers of the National Institute on Deafness and Other Communication Disorders (NIDCD), one of the National Institutes of Health.