One of the most unique aspects of being Human are our communicative abilities and complex languages. It is a complicated process, and such has a lot of neural dedication towards it. Through this we are able to very effectively communicate what goes on in our brains and intricate ideas between other people.
While we normally do not experience communication without language, there is a question about whether these two things are intrinsically linked or if they are functionally distinct. Is it possible to have communication without language?
Specifically, we are interested in Mentalization; the ability to understand the intentions of others, their brainstates, etc.
There is some evidence that suggests language is necessary. If participants are asked to perform a mentalizing task and language task concurrently (the False Belief Task and Verbal Shadowing Task), their performance on the mentalizing False Belief Task decreases (Newton & DeVilliers, 2007). The idea here is that the language task puts a load on the language system, which reduces the resources available to perform mentalization. If these two systems were separate, we would expect people to be able to perform both tasks at the same time at similar performance levels than alone, since they would be using separate neural systems. So this at least implies there is some overlap.
However, fMRI studies have revealed there might really be two systems after all, supporting the notion that the systems are distinct. Researchers reviewed different neuroimaging studies and found a dissociation between mentalization and language. Mentalizing seemed to involve the Medial PreFrontal Cortex (Willems & Varley, 2010). This is distinct from language which involves different areas like the left Inferior Frontal Cortex.
Even more evidence comes from examining the mentalizing capabilities in Aphasic patients. Aphasia is a speech and language disorder that severely or completely impairs language abilities. An aphasic patient can lose the ability to read, write, and speak.
If mentalization is truly inseparable from language, then you might expect that somebody without a functioning language system would be heavily impaired in their ability to mentalize. So Willems et al. (2011) had four aphasic patients participate in a non-verbal communication game to test their abilities to mentalize. Their performance was compared against normal, healthy controls.
The task was called the Tacit Communication Game. In it, two players are shown a simple 3x3 grid with two player-pieces. The goal is for both players to reach a destination square in the least amount of turns possible without being able to speak to each other. The catch is that only one player knows the end-state goals. The other doesn't and must somehow get this information from the first player.
Both players can see the board as pieces are being moved (think of playing chess online), so really the game's success hinges on each players ability to generate and understand a message signaling communicative intention to someone else. Or, in other words, mentalization.
Usually the best strategy is for the first player to move their piece to the second players goal, hang there for a few seconds, and then move to their own goal and end their turn. Them going out of their way and pausing at a location communicates to the other player that this position is important. Assuming both players know they are trying to get to a goal spot on the playing board, the player can figure out that this is where they're supposed to be.
It's not a complex game, and really the challenge comes out of the two players generating an effective communication strategy like this. Remember they are not able to talk to each other. Most experiments of this would probably have the participants in other rooms on computers, so the only thing they can see is the boardspace.
Regardless, it requires communication and mentalization between the participants and does so without needing actual language. This makes it perfect to test with Aphasic patients. If language is intrinsically linked to mentalization, then someone with language impairment should perform worse than a healthy someone, if they are able to do it at all.
But actually, aphasic patients perform just fine in this game! Aphasics all perform well above chance levels, reaching similar levels to controls (Willems et al., 2011). Their strategies end up being similar to controls too, intentionally pausing at the other players goal locations.
So there is good evidence to suggest that mentalizing is distinct from language, involving different processing and being able to work independently from each other. The issue is certainly not definitive, there is much more work to be done to determine precisely the relationship and interactions between these processes, but the situation is definitely more complex than "they are the same thing".
Newton, A. M., & Villiers, J. G. De. (2007). While Talking Thinking. Psychological Science, 18(7), 574–579. doi:10.1111/j.1467-9280.2007.01942.x
Willems, R. M., Benn, Y., Hagoort, P., Toni, I., & Varley, R. (2011). Communicating without a functioning language system: Implications for the role of language in mentalizing. Neuropsychologia, 49(11), 3130–3135. doi:10.1016/j.neuropsychologia.2011.07.023
Willems, R. M., & Varley, R. (2010). Neural insights into the relation between language and communication. Frontiers in Human Neuroscience, 4(October), 1–8. doi:10.3389/fnhum.2010.00203