How much does the brain know about itself?
/“How much does the brain know about itself?
I have been poking around with google and it seems that there are plenty of nerves in the brain, apart from the ones that do the core business, as it were. Maybe it has pretty good knowledge about the energy consumption around the brain, rather in the way that the somatosensory cortex knows about what is going on in or near the skin?
Perhaps you can point me at something which an amateur could understand?”
Great question, Jim! There are many representational maps of the body in the brain, and the brain is a part of the body after all… so how much does the brain ‘know about itself’? I’ll try to address three types of representation here - physical sensations, energy usage, and abstract thought. Let’s start with physical touch.
Touchy Feely
The somatosensory cortex. Source: Wikipedia Commons
You’ve already pointed out the somatosensory cortex, which is a brilliant example of an information map in the brain. It’s a strip of your brain’s surface (‘cortex’) that encodes sensations from different parts of your body. It sits right under where you might rest your sunglasses, at the top of your head (see image to the right).
The sensory homunculus. Source: Wikipedia Commons
The diagram below and to the left shows a slice through the brain, revealing the folded surface of this strip. The body parts drawn along it illustrate which portions of the body are encoded where. The spot at the top left of the diagram will respond to a touch on your hip, the spot a little further right will respond to your torso, then your neck, etc. The order tends to match the layout of your body, as you can see by the arrangement of the parts. This mapping of the body onto the brain is called a sensory ‘homunculus’ (Latin for ‘little man’). As you can see, some body parts are better represented than others - your hands and lips are more sensitive than your thighs, so more space in your brain is devoted to interpreting the extra sensations from those areas.
You may notice that the brain itself isn’t represented in the homunculus at all! That is to say, there is no part of your brain dedicated to generating the sensation of your brain being touched. In fact, if someone were to poke your brain you wouldn’t feel it. It’s possible to open someone’s head up (after anesthetizing their scalp) and prod the surface of their brain while they’re awake. There was actually a recent television special where this was done live as part of a surgery on a patient suffering from Parkinson’s disease. It turns out that if someone stimulates your sensory homunculus, instead of a feeling in your brain you’ll actually feel something in the corresponding parts of your body. The whole system can be run backwards like some kind of brain tissue voodoo doll. Of course nothing too mystical is happening here - we’re just directly stimulating the part of your brain that is normally activated by, say, signals from your hand. This causes your brain to produce the sensation of your hand being touched, even though your hand didn’t actually send any signals. Every sensation you feel, from the tip of your nose to the tip of your toes, is really generated in that little strip of brain at the top of your head. Crazy huh? Since your brain itself isn’t represented there though, it seems that there’s no way to feel it. This makes some sense, as brains normally don’t get touched anyways.
[What about headaches, you ask? We’re not totally sure, but those pains are thought to originate in blood vessels and other non-brain tissue structures]
Food for Thought
There are some other things that would seem pretty useful for the brain to know about itself, though. You mentioned energy use. This is no joke - your brain uses something like 20% of the total energy you consume each day. A full one in five parts of everything you eat! (What does the brain do with all of this energy? Check out Ada Yee’s excellent article on the brain’s energy budget for more information.)
How does your brain know when to call for more fuel?
Well, there are cells in the brain called glia, which are perhaps most accurately defined as “the cells in the brain that are not neurons.” There are at least as many glia in your brain as there are neurons (estimates vary, but Stanford professor and glia expert Ben Barres estimates that they make up at least 80% of cells in the human brain!) There are many different types of glia, and they play a wide variety of critical roles. Some glial cells sense when nearby neurons need more energy and signal for an increase in blood flow by dilating adjacent vessels. The extra blood flowing in these enlarged vessels carries more oxygen to the area and fills the energy need. This process is pretty similar to the way your muscles call for more energy; local signals result in increased blood flow there too.
So glia can call for more energy when the brain tissue around them is running low, but does that mean that they know it’s running low? The answer depends on your definition of ‘know’. Does your biceps know when it’s running out of energy? Does a toilet know when its tank is full and it can stop refilling? Obviously (for most humans, at least) a brain is a much more complicated system than a toilet, but it’s unclear whether these sorts of feedback loops should be considered to ‘know’ things. This is a question of philosophy, but I’d argue that knowing something requires simplification or abstraction. The brain doesn’t seem to have any scale maps of its energy use, each part just keeps track of itself. If the sensory homunculus is a little map that represents what your body is sensing, these local energy signals are at best a map of the brain that’s the same size as the brain itself. Just like a town map the size of the real town wouldn’t be very helpful, this doesn’t provide the kind of abstraction that I would consider ‘representational knowledge’.
Oh, the Places You'll Know
The Hippocampus located within the Human Brain. Adapted from Gray's Anatomy, Plate 739. Source: Wikipedia Commons
Energy use aside then, does the brain store any abstract knowledge about itself? Well, as a physicalist I believe that everything we know and experience has a physical basis in the brain. If you agree with me, then that means your brain physically contains everything you know about brains! Figuring out where and how this sort of information is stored is still a major question in neuroscience, but we have some leads. For example, it’s thought that memories are initially processed in the hippocampus - a little curvy bit deep in your brain, so named because it looks kind of like a seahorse (Hippocampus is the seahorse genus).
Later, memories are probably transitioned to wide-spread storage all around the brain’s surface (cortex). This process is called consolidation, and it’s one of the main things thought to happen during sleep. Now that I’ve told you this, it’s possible that these facts are sitting in your hippocampus as you read this! In some way, your hippocampus may be representing the idea that it looks like a little seahorse! Wherever that idea might end up encoded in the long run, for the moment we can say that at least one small part of your brain really knows something about itself.
Left: Human Hippocampus. Right: Seahorse. Both: Humanity's boundless ability for thinking one thing looks like another thing. Prepared by Laszlo Seress, 1980. Source: Wikipedia Commons
