Unlike other touch receptors, which operate on a loop—you touch a hot stove, the nerves fire a signal to the brain, the brain registers pain and fires a sign

Unlike other touch receptors, which operate on a loop—you touch a hot stove, the nerves fire a signal to the brain, the brain registers pain and fires a signal back for you to withdraw your hand—these receptors are one-way. They talk to the brain, but the brain doesn’t communicate back. “We think that’s what they exist for, to trigger endorphin responses as a consequence of grooming,” Dunbar said. Until social media can replicate that touch, it can’t fully replicate social bonding. Crazy thought: Could the haptic-messaging features of the Apple Watch make it the first mainstream product to tap into this principle?