How Much do You Know About Your Own Brain?

We tend to believe we're aware of what's happening in our own brains, and also in conscious control of our behavior.  But a growing body of neuroscience and psychology research demonstrates that most of what happens inside the brain-- including the processes that cause us to select and execute behaviors-- is beyond our conscious awareness.  This has important implications for our eating behavior, body weight, and health, as I explore in my upcoming book The Hungry Brain.

Let me give you a straightforward example that illustrates how little of our brain's activity we're aware of.  It focuses on information processing by the visual system, which is one of the best-understood systems of the brain.  I drew the basic facts of this example from a recent talk by the accomplished neuroscience researcher Marcus Raichle, who studies patterns of activity in the human brain.


Consider the retina of the eye.  It's composed of more than 100 million light-sensitive cells called photoreceptors.  These cells capture ten billion (10^10) bits of information per second from your visual surroundings.  That's a huge amount of information!  In fact, it's far too much for the brain to process effectively.

Before the information even leaves the retina, it goes through its first stage of processing and compression.  By the time the information enters the optic nerve that connects the retina to the brain, it has been compressed down to six million (6 x 10^6) bits per second-- a reduction of nearly 1,700-fold.  This is because, instead of passing along a precise copy of the visual field, the retina begins extracting salient information from it and passing that along instead.  This is similar to how image compression works on your computer (e.g., bitmap to JPEG format).

But the compression doesn't end there.  Once the information reaches the visual cortex of your brain, it's compressed down to ten thousand (10^4) bits per second.  The brain does this by further extracting meaningful information from the retinal data, translating it into increasingly abstract terms, and ignoring irrelevant information.  Now the information is starting to resemble vector graphics more than a JPEG file.  Rather than specifying the position of individual "pixels", the information denotes patterns and objects and how they're moving.

From the visual cortex, researchers estimate that less than 100 (10^2) bits per second of visual information reaches our conscious awareness.  That's only 0.000001 percent of the information your retinal photoreceptors registered, and 0.01 percent of the information that entered your brain.  This information is highly processed and filtered-- so much so, that it's predominantly conceptual at that point.  You don't see each individual hair on your friend's head and each stitch in his Christmas sweater; you just see your friend wearing a Christmas sweater with reindeer on it.  And if something irrelevant is happening behind him, you don't see it at all.  If you don't believe that, watch this video.

Since the processing power of the conscious brain is quite limited, the non-conscious brain feeds it information on a need-to-know basis.  You may not actually be consciously seeing much at all if you're listening to something intently, and you probably won't see something in your left visual field if you're paying attention to the right.  Yet, non-conscious parts of your brain are still monitoring everything outside and inside your body, looking for important signals that could be worth alerting the conscious brain.  For example, if you're trying to cross the street and something large in your peripheral vision is moving rapidly toward you, it will get your attention even if you were focusing on a billboard a moment ago.

This is consistent with the research of the Nobel Prize-winning psychologist Daniel Kahneman, who wrote the wonderful book Thinking, Fast and Slow.  Kahneman contends that the brain can be conceptually divided into two "systems".  System 1 is fast, intuitive, automatic, and non-conscious.  System 2 is slow, effortful, deliberative, and conscious.  Since system 2 is what we perceive, we think it's who we are, but in fact Kahneman believes that system 1 does most of our processing and guides most of our everyday behaviors.  System 1 is not one thing, but rather a diverse collection of ancient, non-conscious brain circuits.

The visual system example I explained above is one illustration of how neuroscience research supports Kahneman's idea.  What we perceive is only a small fraction of what's happening inside our very own brains!  That's kind of amazing, isn't it?  It's also counterintuitive, because we aren't aware of what we can't perceive, so we tend to intuitively think that our conscious brain is all that exists.

My primary interests are eating behavior and body fatness, and that's what my book is about.  As it turns out, the idea that our brains are primarily non-conscious has important implications for understanding how we eat and what we weigh.  If we're primarily conscious, rational beings, then the best way to guide our behavior in a slimming direction is to consciously regulate the number of calories entering and leaving the body.  This is typified by the "eat less, move more" approach to weight loss, which works extremely well in metabolic ward studies where behavior is externally controlled, but not so well in real life.

On the other hand, if our behavior is often guided by non-conscious processes that are more impulsive than rational, we'll need a different approach: identify the signals that influence these processes, and provide signals that align our impulses with our conscious goals of leanness and health.

While both the conscious and the non-conscious brain are important for behavior, ultimately I believe we'll get better, easier, and more sustainable outcomes by acknowledging that the non-conscious brain is often holding the reins of our behavior.