These waves are classified by how frequently the neurons fire in a single second. If they fire one to four times, that’s a delta wave, which occurs during deep sleep. If they fire 12 to 30 times, that’s a beta wave, which is typical of normal wakefulness. And if they do so 30 to 90 times, that’s a gamma wave, which has been linked to higher mental abilities, like memory, attention, and perception. It’s no surprise, then, that scientists have seen disrupted gamma waves in many types of brain disorders, including injuries, schizophrenia, and Alzheimer’s disease