When other people’s minds are within your grasp: Motor cognition of theories of mind

Humans are social beings and by and large we understand each other. In particular, we have a sense of how others are feeling and what others might be thinking or what information they have access to. If your spouse calls you on the phone to ask whether you can find the wallet that they forgot at home, you are unlikely to point to it when you see it lying on the table. Instead, you will say something because you know that gestures don’t travel well through phone lines.

Although this ability to know what others know comes natural to adults, we need to learn about it as we grow up. Children at a young age often lack this ability, known as a Theory of Mind, and so they fail to recognize what other people can and cannot know:

Fortunately, growing up just a little can help a lot:

Having a Theory of Mind is so essential to normal social and cognitive functioning that we can readily perceive a failure as amusing: who hasn’t met the stranger on the bus who tells you all about his uncle Bruce’s carbuncle, seemingly oblivious to your ignorance of—and lack of interest in—uncle whatshisname.

For decades, most researchers have considered a Theory of Mind to be the predominant—or perhaps even the only —way to access the minds of other people. However, recent thinking and theorizing has moved away from this unitary view of a Theory of Mind, and the concept has been augmented by a more nuanced and multi-layered way of thinking about how we can put ourselves into others’ mental shoes.

In a recent article in the Psychonomic Society’s journal Cognitive, Affective, & Behavioral Neuroscience, researchers Casartelli and Chiamulera review and extend some of this recent work. At the heart of their proposal is the notion of “motor cognition”—that is, the idea that the same brain system that plans our bodily movements can also help us understand and shape human behavior. Casartelli and Chiamulera argue that “we can have (also) direct, pre-cognitive, and motor understanding of others’ behavior.

To illustrate how early such non-mentalistic social abilities develop, and how “pre-cognitive” (i.e., requiring no explicit thought) they are, consider the fact that newborns at the tender age of 2 days prefer biological motion to artificially animated motion. This is not entirely surprising given that our ancestors’ survival depended on rapid discrimination between the movement of a potential predator and a nonbiological movement such as a dislodged rock rolling down a hill.

Similarly, we can attach an immediate (i.e. motor) “social” interpretation to others’ movements. Casartelli and Chiamulera cite the example of an espresso cup: if your friend grasps the cup by the handle, you immediately know that they intend to drink it. If they grasp the cup by its body, with the handle pointing towards you, then you also instantly know that they are treating you to a coffee.

One could argue that even this interpretation of someone’s grasp of a coffee cup necessarily requires some high-level cognitive involvement—that is, some aspect of a Theory of Mind. Casartelli and Chiamulera argue against this possibility by citing a large body of evidence involving mirror neurons and motor resonance mechanisms. Mirror neurons were first observed in primates and their name represents the fact that they fire both when an animal acts and when the animal observes the same action performed by another actor. Intriguingly, mirror neurons tend to be tuned to the goal or the meaning of an action, rather than the particulars of the motion involved. That is, a monkey’s mirror neurons will fire irrespective of whether the animal itself breaks a peanut, whether the animal hears the sound of a breaking peanut, or whether the human experimenter is observed breaking the peanut.

The fact that mirror neurons, typically located in areas of the brain dedicated to motor movements, can encode the abstract meaning of an action with such generality has radically modified the traditional view of the motor system. It is no longer seen as a mere robotic controller of mechanical body motions, but as a system capable of “social” representation.

Against this background, Casartelli and Chiamulera tackle the potential involvement of motor cognition in autism spectrum disorder (or ASD for short). People with ASD tend to have impaired social interactions and communication problems from an early age onward. Additional behaviors that are diagnostic of ASD include restricted and repetitive patterns of activities (e.g., switching lights on and off or opening and shutting doors).

Can the social difficulties experienced by people with ASD be attributed—at least partially—to deficiencies in motor cognition? There is much research that has documented motor deficiencies in people with ASD: although those motor deficiencies—such as fine motor coordination during writing—do not directly impact on social abilities, Casartelli and Chiamulera propose a link based on some intriguing research  involving electromyography (EMG). EMG records the activity of muscles, and in one crucial study conducted by a team of researchers led by Luigi Cattaneo and Rizzolatti’s group, children observed an experimenter reaching for a piece of food in the table in front of them and eating it while the activity of their mouth-opening muscle was recorded.

If you observe someone else reaching for food, what does your mouth do? The figure below from the study by Cattaneo and colleagues shows that in typically-developing children, the mouth muscles work overtime while observing someone reach for food (red line), even before the hand touches the food (at time 0). The mouth remains unmoved by observing the same person reach for a piece of paper instead (blue line).

Now compare this motor pattern with that of children with autism:

It is quite clear that children with autism do not “mirror” the implications of another’s actions.

In a further experiment, the two groups of children performed the actions themselves. In this case the mouth of the typically-developing children started moving already while they were reaching for the food (but not the paper), whereas the children with autism showed no sign of their mouth being engaged until after they grasped the food and brought it towards their mouth.

Casartelli and Chiamulera conclude that “ASD children seem unable to encode the meaning of action (i.e., the motor intentionality, to eat vs. to place) in a motor way” (their emphasis). Children with autism may not fail to understand intentionality and actions altogether, but it appears as though they have difficulties relying on motor cognition to code socially-relevant intentions or actions.

There is clearly a lot more to planning simple movements than just getting your fingers to grasp that espresso that your friend is holding by the body of the cup, not the handle.

Article focused on in this post:

Casartelli, L., & Chiamulera, C. (2016). The motor way: Clinical implications of understanding and shaping actions with the motor system in autism and drug addiction. Cognitive, Affective, & Behavioral Neuroscience. DOI: 10.3758/s13415-015-0399-7.

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