All gestures are not created equal. There are the “you go, no really, okay, I’ll go” gestures that we use to indicate whose turn it is to tell a ghost story around the campfire, and there are the hacking gestures we use to Emphasize. Our displeasure. That the neighbor’s campfire. Just burned. Our house. To the ground. These types of gestures communicate information, but information without content. The “okay, I’ll go” gesture doesn’t have much to do with the story I intend to tell when my turn finally comes.

Other types of gestures, however, known to researchers as representational gestures, are at least somewhat iconic, reflecting the content of a speaker’s message. When we point to our smoldering house as we inquire as to the status of our last insurance payment, or when we drag our hand slowly across our body while describing the speed with which the fire department rushed to our rescue, we are using representational gestures to augment the message we wish to convey.

Last week, I described the very real possibility that, in order to understand a sentence like He climbed up the tree, we may have to mentally simulate climbing up a tree. In the process, we’ll activate many of same parts of our brain that are necessary for, well, actually climbing trees. Most psychologists that subscribe to this theory, known as embodied cognition, are of the opinion that language production occurs in much the same way: in order to access the concept climbed up the tree for speech, relevant cortices must be activated.

Martha Alibali, a psychologist at University of Wisconsin-Madison, has theorized that representational gestures emerge as a consequence of these mental simulations. Why do gestures tend to accompany language production, but not comprehension? It appears that our mouth and hands are closely linked in the brain. Not only do they take up much more than their share (size-wise) of the premotor and motor cortices, but neurons responsible for one brush shoulders—er, touch lips—with the other. And from birth the two can already move together in highly coordinated ways. (When babies babble ga-ga-ga, for example, they often move their hands to the beat.) Alibali reasons that this special relationship may allow some of the motor information we’ve activated for speech to spill over from the mouth to the hand.

Representational gesturing, one line of thinking has it, lets us break an important or tricky concept into parts that can be more easily verbalized. Thus, when we really want people to understand that the fire spread from the porch to the fireplace (absolutely not the other way around), we allow more motor information to spill over than we otherwise would. Indeed, it actually takes work not to gesture when we’re having a tough time getting our point across. When researchers have prevented people from gesturing while trying to think of words—inferno, say, or criminal negligence—they are less likely to successfully retrieve them.

There are cultural differences in the size and frequency of our gestures—falling, more often than not, along stereotypical lines (want to hazard a guess about whether the Italians or the Japanese gesture more boisterously?)—but we all gesture. The blind even gesture to the blind. As both artifact and facilitator, gestures may prove to be as much a part of speaking as speech itself.