Plato on how the brain and body influence each other

As I said last time, Plato takes up the Homeric concepts of ‘psyche’, ‘thymos’ and ‘phrenes’ and develops a detailed theory with various similarities and differences to the originals. I also explained that Plato realized that if we could figure out how the living body of a being registers stimuli, it would go a long way toward us understanding how the more intelligent system, the perceptive consciousness of a human, works. He originally set out his theory in his classic Republic (audio), but he offers an extended, more ‘scientific’ discussion of the interplay between mind and emotion in the Timaeus.

Plato holding his copy of the Timaeus


His major theoretical development is to talk about the mind as having a tripartite nature, and argues that it is this that allows us to move beyond the child-like behavior of the Iladic people. Upon thinking about human capabilities and behavior, Plato argues that it seems certain that unlike merely conscious animals, humans depend upon two “mental’ systems to live and interact with the world. One is found throughout the body, focused in the chest, and the second is localized at the brain and interconnected with the first one.

Let’s call the first, more basic system ‘body-psyche’. It is basically what today we’d call the central nervous system and its job is to take in the literally “necessary disturbances” of life, such as pleasures and pain, while also being the source of others such as boldness, fear, anger and expectation. Note that all of these are tools necessary for dogs as well as humans to survive, and they are at the core of the ability to socialize. The mental activities of the body-psyche are still aligned closely with simple ‘unreasoning’ awareness (e.g. lusting).

Plato notes, however that humans can sometimes overcome lust and other such unreasoning awareness, but other animals, such as dogs in heat, cannot. This leads Plato to say that the body-psyche appears to be ‘separated’ from the other psyche, the one capable of reasoning, as if by some barrier.

An example of the rational part of the psyche doing its thing


But what is this barrier, what distinguishes the brain-psyche from the body psyche? Plato answers that it stands to reason that something in or about the (human) brain allows for our ability to sometimes overcome unreasoning awareness. (And he thinks, somewhat naively, that it’s quite important that the brain is geographically separated from the rest of the ‘mind-system’ by the neck.)

At this point you may be thinking this two-part distinction is pretty clear cut and are wondering how he’s going to find a third “part” to distinguish. Plato thinks it overly simplifies what is going on, but to move forward he has to write you a check and promise to cash it a little later. He asks a series of probing questions: Do we as a matter of fact note any mental activity at all that is neither pure reasoning nor unreasoning awareness? Is it is possible to explain how such activity is created physiologically? Is there any benefit to pursuing this speculation? He answers “yes!” to all of these.

Getting a better view

Let’s take a step back to look at what is going on here, what Plato is doing. He is in the business of trying to understand how simple awareness and perceptive consciousness work and linking them to higher cognitive functions such as abstract thought. He’s committed to a physiological relationship between them that runs: registering (seeing, hearing, feeling a thing)à consciousness (being aware of and paying attention to the thing) à higher cognition (reasoning about the thing).

So we think that there’s more to the story about perception and mentality than the Iladic story can explain and we’ve got the brain-psyche on one hand and the body-psyche on the other. Plato then stipulates that the bodily psyche itself has two parts. The superior part of the bodily psyche has the following properties: it exhibits “spirit” and ambition; it is physically closer to the brain; it can and does listen to and work with reason; it forces compliance from the (lower) part of the body-psyche that consists of appetites, as for food and sex.

Plato gives a lot of reasons why human physiology supports this view. To show the reality and power of the ‘lower” body psyche, he notes that no humans, in fact no animals at all, could exist if the appetite for things the body needs such as food and rest were not 1) sustained and continual and 2) strongly felt. In fact, this set of necessities we call appetites constantly need satisfaction; I’m sure you know how hard it is to think straight when you’re starving or really have to relieve yourself. Further, when we look at how the heart works and how we can raise and lower our heart rate, we get an idea of how ‘reason’ can use the body to exert its will on the body.

To better explain what the “superior” bodily psyche is, Plato says that by and large the appetites don’t “understand” the deliverances of reason and to the extent they do, they have no innate regard for reason. Instead, it appears to common sense that appetites are enticed – and so controlled – by “images”, they react immediately to what they see. However, the superior body psyche, which I can now tell you is the emotion center, clearly does respond to reason. After all, many people, probably even you, have appetites or desires for things that you wish you didn’t. In fact, many people have desires for things that they really are embarrassed by, and they get really mad at themselves for indulging them. So mad, even, that they often can force themselves to stop. Plato thinks that the fact you can be aware of, judge negatively, and cease to act on an appetite is evidence enough that the reasoning capacity can work in concert with something – the emotions – to control the appetites.

Now the details of the physiology Plato gives us as to how this works are not very useful so I’ll bypass them, and happily, his psychological theories are not dependent on the details. He’s not working from the way the organs actually work and building out a psychology that fits on top. Instead he starts from experience and behavior and is looking to see if there’s a plausible way to account for his theories based on human physiology.

It is useful is to note that he was trying to meet the scientific data he had and at the same time answer a difficult problem as honestly and intuitively as possible, with as much explanatory power as possible. His conclusion was a psychology that says mind consists of three “parts” the psyche which is capable of abstract thought and can control the body, the thymos or “spirited” part, which is our emotion center, and the phrenes, which Plato casts as the appetitive part.

Cashing the check

Remember the end point we’re working towards: Plato thinks we can better understand the mind and human behavior if we move beyond the simple views that our minds are our thymos and that all mental activity is like that of the Iladic people or children, a sort of “hot thinking”. He believes that we can gain great explanatory power from looking at human mental capacity as consisting in three physically interconnected “parts” that will account both for hot thinking and cooler thinking, and that based on how human physiology is set up, the how behind the things this theory suggests happen is plausible. Here’s a high-level synopsis:

1. In humans as with other animals, appetites or desires typically run on their own. All things being equal, when an appetite strikes, humans, like other animals, ‘mindlessly’ pursue it. This much covers how any animal conscious being comes to feel pleasure and pain, and how they affect action. But Plato also wants to explain how humans are not only animal conscious but self conscious and how the two are related.

2. Sometimes, instead, in humans the emotion center (thymos, or superior body-psyche) communicates to the appetites what our reasoning part wants done about a situation, such as whether or not to pursue satisfaction as well as how better to do so.

3. Whatever the communication between these parts is done with, it must be a way that is ‘understandable’ for the appetites. It appears to be a physical messaging system that uses various bodily fluids to affect the vital organs such that the body can be put into various states such as pain and nausea, which have a very strong influence on the will or the desire to pursue a course of action. In fact, these states are strong enough to undermine the otherwise very strong urge to satisfy a currently active desire and replace it with another one supplied by reason.

4. The reasoning part of the mind, in conjunction with the emotions, is able to manipulate the proper physical changes in the body, thus sending the proper message of pleasure or pain to silence (or strengthen) the basic pangs that are messages of appetite. Of course these appetite messages can also be very strong and overpower the inclination to do things that require intelligent thought. These messages go back and forth between the body and the brain, with varying degrees of success. (Going forward we’ll refer to this process as duplex communication).

5. For example, let’s say you have the desire to do something you think is awful, like kicking a puppy that’s been yapping for too long. You kick it and realize the poor thing was just looking for attention and now you’ve seriously hurt it and as you get a sick ‘guilty’ feeling in your stomach, the anger you felt about the yapping disappears, along with the desire to punish the animal, you feel sorry and promise to yourself never to needlessly attack a defenseless animal again.

To strengthen this idea of duplex communication, Plato argues that its clear that bodily conditions can cause illnesses in the brain-psyche, thus stopping it from working as it often can to control our behavior:

  1. “Mindlessness”: Either ignorance or madness. In the first case, your physical need to eat or to go to the bathroom can become so strong that you are no longer aware of your surroundings. In the second, you literally lose touch with reality due to things such as lack of sleep or syphilis.
  1. “Excessive pleasure or pain”: too much of either leads to an inappropriate level of exertion, which undermines the ability to hear anything correctly. Think of an addict, of drugs, sex, video games, attention or whatever. They like the thing too much, such that they focus way too much energy on obtaining it and they can’t ‘hear’ things such as the demands of their body, their boss, spouse, friends, etc.

In the next post I’ll give a more detailed discussion of these three parts of the mind, and further explain the benefits of the view for understanding the connection between the emotions and morality.


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