Are the mind and body separate? They may be in perception

In the history of thought, the idea that the mind and body are separate has been hotly debated. Probably the most famous statement of mind/body dualism is from the philosopher René Descartes, who in the 17th century argued that there are two different kinds of stuff in the world: stuff extended in space (such as chairs, computers, and human bodies) and stuff which lacks extension but somehow exists as an immaterial substance (the human mind). So, are the mind and body separate?

How should I know? I'm a psychologist.

So instead of asking that question, let's think about a similar, yet very different question: Are the mind and body separate in our perception of and thoughts about other people? We typically experience the two as separate. Most people think, for example, that a human body just before and after death somehow changes in a simple yet dramatic way: before, it had a mind; after, it does not. A lot of people think that, though the body may change over time, essential features of the mind do not; that, in a sense, there is something inside of our bodies - the mind - that stays constant over time, and that to some, even exists before birth and after death.

We perceive minds and bodies differently, too. Bodies, we see. Minds, we... well... we don't really see them, do we? When we see a person, we see their body and the movements of their body. We see what their body is interacting with in the physical environment around it. We hear the sounds their body makes. When we touch or are touched by a person, it's their body that we touch or does the touching. In perception, all we have access to is the stuff that the other person's body is doing. We don't see the mind; we don't hear the mind; we don't feel the mind; and we can't touch the mind. Despite the invisibility of the mind, we still have little trouble understanding what is (or is most likely) on other people's minds. For example, if you see someone pick up a sandwich and move it towards their mouth, you can easily infer they probably want the sandwich because they've got hunger on their minds. Safe bet, right? If you see someone give a homeless person a dollar, you can infer the person giving the dollar away is generous (a stable trait of the mind) or in the least intends to be generous in that moment. A safe bet, but not as obvious. Maybe the person feels guilty, and therefore gives the dollar in order to reduce guilt. We don't know. Why don't we know? We can't see the mind. Rather, we see only what bodies do. Still, most of us rarely experience a great deal of trouble making educated guesses about what's on other people's minds.

In the social and cognitive neurosciences, there is accumulating evidence that there are two separate systems in the brain, one we use for understanding the behavior of bodies, and one we use for understanding the behavior of minds. The "Body Understanding System" consists of regions of the brain involved in seeing stuff (visual areas), recognizing stuff we see (object recognition areas), feeling stuff (somatosensory areas), and moving stuff (motor areas) (for reviews, see Bastiaansen, Thioux, & Keysers, 2009; Martin, 2007) . The first two sets of areas (visual and object recognition) aren't so surprising, but the last two may seem a little surprising. Motor and somatosensory areas of the brain are believed to be rich in a special kind of cell called a "mirror neuron". Mirror neurons are special because they fire when you do stuff AND when you see others doing the same (or similar) stuff (Rizzolatti & Sinigaglia, 2010). There's plenty of controversy surrounding what mirror neurons do and whether they matter for humans, but all you need to know is that they don't distinguish between you and the other person when it comes to stuff going on with their body. If you see someone reaching for a sandwich, your brain areas for seeing and recognizing sandwiches activate, as do your brain areas for picking up sandwiches yourself (and potentially also your brain areas for the "feel" of a sandwich in your hand). This allows you to connect with the other person's body in a way that enables understanding their behavior. Ever smiled for no apparent reason other than the fact that someone you can see has smiled? Ever teared up when seeing another person crying? That's your mirror neurons connecting your body to another. Or at least that's how the story goes.

Now for minds. Again, there's a lot of controversy over what mirror neurons do. One of those controversies regards their role in understanding other people's minds. Suffice to say, there's a lot of evidence to suggest that the areas of the brain most people associate with mirror neurons - that is, motor and somatosensory areas - don't seem to be necessarily involved in "seeing" the minds of others. Rather, the "Mind Understanding System" - which is a motley crew of brain regions that are not primarily involved in motor or somatosensory processes (that is, in moving stuff and feeling stuff) - is involved when people think about the minds of other people (e.g., what people want, what people believe, what people intend, people's moral sense, people's personality). I won't give you a laundry list of region names, other than say that these areas have been associated with a lot, including mental imagery, memory for personal episodes, memory for people's names, memory for abstract knowledge, and holding information about other people in mind (for reviews, see Frith & Frith, 2006; Van Overwalle & Baetens, 2009) . Moreover, I'll say that they're not the same regions as those in the "Body Understanding System".

To provide a simple (and somewhat self-serving) example, if you have people think about WHY people perform actions (e.g., Q: Why do people blog? A: Fame and fortune, of course) versus HOW people perform actions (e.g., Q: How do people blog? A: Type type type), they use the "Mind Understanding System" for the why question and the "Body Understanding System" for the how question (Spunt, Falk & Lieberman, 2010). Though it may seem that these two questions - How? and Why? - are not all that different, we use different systems in our brain to answer them, at least when thinking about people. This is because the how question typically makes us think of what the body needs to do in order to get the action done, while the why question makes us think of the state of mind associated with doing the action.

So it seems that, in our perception of others (and perhaps of ourselves), there may be some fundamental differences between (the way we process) bodies and minds. Maybe we see them as separate because we "see" them using separate psychological processes.

Thanks to my research mentor, Dr. Matthew D. Lieberman, for the basic idea behind this post.

References

Bastiaansen et al. Evidence for mirror systems in emotions. Philosophical Transactions of the Royal Society B: Biological Sciences (2009) vol. 364 (1528) pp. 2391

Frith and Frith. The neural basis of mentalizing. Neuron (2006) vol. 50 (4) pp. 531-4

Keysers and Gazzola. Towards a unifying neural theory of social cognition. Progress in brain research (2006) vol. 156 pp. 379-401

Keysers et al. Somatosensation in social perception. Nat Rev Neurosci (2010) vol. 11 (6) pp. 417-28

Martin. The representation of object concepts in the brain. Annual Review of Psychology (2007) vol. 58 pp. 25-45

Van Overwalle and Baetens. Understanding others' actions and goals by mirror and mentalizing systems: A meta-analysis. NeuroImage (2009) vol. 48 (3) pp. 564-584

Rizzolatti and Sinigaglia. The functional role of the parieto-frontal mirror circuit: interpretations and misinterpretations. Nat Rev Neurosci (2010) vol. 11 (4) pp. 264-274

Spunt et al. Dissociable Neural Systems Support Retrieval of How and Why Action Knowledge. Psychological science (2010), 21, 1593-1598