Posted September 14, 2014 by Bernard J. Baars in coma
 
 

Be nice to your Precuneus – it might be your real self…

The hardest thing about the brain is learning the labels. Let’s take the Precuneus as example. It’s one of the most important parts of our brains, so much that we would be totally lost without it (Literally).  In fact, the Precuneus may be the most basic “seat of the self.”

Other areas of cortex do self-like jobs, too: For example, the prefrontal cortex does executive functions like decision-making.

But Precuneus may involve the “observing ego” — the “I” we talk about in everyday conversation. It’s the point of view of the self on the world.

Here is how the Precuneus looks when we divide the brain in half like a melon, and look at the inside of the right half, nose pointing to the left. If you find that confusing, just hold out your two fists, thumb to thumb, and pretend your right fist is your right hemisphere, left fist left hemisphere. It makes it easier to visualize the brain in three dimensions.

Precuneus

The Seat of the Self? Something close to it. It lives on the inside of each cortical hemisphere, and is associated with “self reflection”.

But nobody knows what the word “Precuneus” means, because we no longer speak Latin as the standard language of science.

Brain labels go back to the first really accurate atlas of human body, published in 1564 by Andreas Vesalius, with fantastic illustrations by an unknown artist who may have been a pupil of the great Italian painter Titian.

It was the Renaissance that brought us our fundamental knowledge of the brain — as far as it can be seen with the naked eye. Since 1564 brain anatomy has been studied at smaller and smaller scales, and it goes on even today.

Since everybody in science used Latin at that time, our brain words come from that language. If we could magically translate brain words into English we’d be pleasantly surprised by how simple they are. The first anatomists simply called what they saw by everyday names.

For example:

1. Cerebrum = brain

2. Cerebellum = little brain

3. Hemisphere = half sphere

4. Cortex = bark (like a tree)

5. Thalamus = bridal chamber (a sexual association — try looking at the thalamus on top of the brainstem)

6. Cuneus = wedge

7. Precuneus = area in front of the wedge. (In Latin the prefix “pre” means “in front of”).

Now you can see why they called the reddish area in Figure “in front of the wedge.”

Looking at the brain with the naked eye, the “wedge” is the triangular area at the back of the brain, where visual areas are located.

Various lines of evidence indicate that the Precuneus is involved in self-related activities. But all conscious experiences involve an implicit self — we see, we hear, we love or hate. Some unconscious activities do NOT seem to be self-related the way conscious experiences are. As the philosopher Immanuel Kant argued two centuries ago, consciousness can be thought of as a process of adaptation of the self to the world. Only very rarely are people conscious of something without relating it to themselves. Even a baby crawling on a carpet must be able to tell when she is coming closer to a toy.

The cortex is equipped with egocentric maps that located one’s own body with respect to other things in the surroundings. These maps reside in the parietal lobe, and the Precuneus is a piece of parietal lobe that flops over on the inner wall of each hemisphere. In brain jargon, Precuneus is the “medial aspect” of the parietal lobe.

So what happens when you lose your Precuneus? There is some evidence that your state of consciousness changes very profoundly.

Patients with brain damage may lose consciousness. With moderate impairment they may go into Minimal Conscious States (MCS), showing  intermittent periods of fairly normal waking. But with more severe damage they are diagnosed as Persistent Vegetative State (PVS) — showing normal vital functions like breathing, and even the basic signs of sleep and waking, but very few signs of normal conscious functioning.

Some scientists believe the difference between MCS and PVS is activation of the Precuneus, a possible seat of the self.

A good discussion on the role of Precuneus and self, MCS and PVS may be found here, at the Neurocritic blog.

(h/t to Neurocritic and medical scientists like Steven Laureys and Niko Schiff, who have made immense progress on comatose states in the last few decades.)

PS. If you want to visualize where the Precuneus is located in the brain, there is a neat rotating brain animation here


Bernard J. Baars