First, a disclaimer: I'm neither a psychologist nor a neurologist. My understanding of these things comes from the sorts of books and blogs I like to read, and podcasts I like to listen to. Usually, the sources they come from are experts (often actual psychologists and neuro-scientists), so I'm pretty confident in their reliability. That said, I'm going to be reproducing a lay-person's understanding of these things, which is probably not a reliable source (read: it's probably way over-simplified and most likely wrong in a lot ways). If you're interested in a more detailed (and probably more accurate) understanding of this, I'd suggest further reading. But I hope you'll find this a useful and enlightening starting point.
The first thing we need to agree on is that the brain is where all the action happens. It's not only where memories are stored, but it's where all sensory information is processed and consciousness is somehow generated. We know that this is true, because decades of medical records show that damage to the brain impairs the ability to recall memories, to perform tasks and to process sensory information.
But it goes one step further: damage to specific parts of the brain can impair specific functions. That implies that the brain has a kind of modular structure: different bits have different functions. When they work together they do the things we know the brain does. Neuro-scientists have very sophisticated instruments that can observe those different areas operating distinctly, but together, and working to produce the subjective experience of life.
But they've also learned some other interesting things. When a certain part of the brain is damaged, the person isn't necessarily aware of the damage. They might not even notice that a certain set of tasks they used to be able to perform are no longer available to them. This could be some missing memories, an inability to recognise faces, even an inability to see (something you'd think people might notice!).
What that tells us is that the brain isn't very good at internal diagnostics. It's not really capable of doing a self-check to make sure that everything's in working order... it just keeps going as if the damaged part is working normally. That means that our conscious experience doesn't really include any awareness of how our brain is functioning: There are processes going on inside us that we're completely unaware of, even in a perfectly healthy brain.
Another important point is the way the different parts of the brain are put together. They're not just all squeezed together in a lump - there's a specific structure at work. To understand this structure better, we need to understand a little about evolution.
Although all living things on Earth are related to each other, not all living things have brains. Only a small portion of us have those. Most multi-cellular animals have a kind of nervous system - a specific set of cells that act as a communications network between the the various parts of the body. The nervous system helps to coordinate things, like moving around, breathing, eating, pumping blood and so on. Many of the more complex kinds of animals have a central core, where the processing of commands for the nervous system happens - that's what the brain is.
Larger and more complex animals have brains that can do more than just coordinate things and process sensory information: they can store memories, evaluate threats in the environment and make decisions about how to react to a given set of circumstances.
A small sub-set of those can do even more complicated things: they can recognise specific individual members of their own species (which allows them to interact socially and collaborate on rearing offspring), they can coordinate activities like hunting or evading a predator. A tiny minority can even think in abstract terms: Recognising themselves in a mirror, inventing and using tools and constructing complex communication systems. Humans are a member of that minority.
Over many millions of years of evolution, our ancestors started out with a primitive nervous system, then developed a brain. That brain grew in complexity, and new regions and areas grew out of old ones, until now we have the familiar-looking brain we recognise. An important thing to note is that those old, primitive brain regions haven't gone away - they're still a part of our brains today. Evolution has just added new 'modules' to the brain, piling them up, one on top of the other.
So when we look at the structure of the human brain, we see the oldest, simplest structures at the bottom (the spinal cord) and the newest, most complex parts at the top (the frontal lobe). Those old structures still do what they always have (coordinating bodily functions and processing sensory information) and the newer parts do the things we tend to think of as being uniquely human (compassion for others, planning for the future, art, logic, philosophy, language and so on). The cerebral cortex is also the part where most of our consciousness happens.
The brain is also wired up according to that pattern of development. Since the eyes developed long before the cerebral cortex, the part of the brain that processes visual information sits in one of the older parts. There's also a part of the cerebral cortex devoted to processing visual information, but it only does so once the older part of the brain has had its first pass. We know this because there is a condition where people have damage to the visual cortex, and thus are unable to see - but they can somehow still evade obstacles in their path. This means they're still processing visual information, but that information isn't being passed through to the conscious mind.
This is important, because it seems that there's another part of the brain, separate from the conscious mind, that makes decisions.
That's what researchers see in experiments. Neuro-scientists have a very useful tool called functional Magnetic Resonance Imaging (fMRI) which allows them to look at a brain as it's working. They're able to plot out the parts of the brain which are busy by literally seeing which bits light up on the screen while the test subject performs a task.
|"I like the pretty lights"|
When a test subject is given a choice to make, the first part of the brain to light up is the limbic system. This is a group of components of the brain that form part of the "brain-stem" - a very old part of the brain, just above the spinal cord. This is a part of the brain known to be associated with emotion and processing sensory information (also where the famous "fight-or-flight" reaction lives). Once the subject has made the decision, the reasoning and creative parts of the brain light up, as they start to explain how they arrived at that decision.
So what does that tell us?
It strongly implies that it's our primitive mammalian (or even reptillian) parts that are in charge of making decisions. The 'higher' brain functions are then tasked with rationalising those decisions after they've already been made.
Let's think about that for a little while. It means that the little ferret-like thing living inside you (the legacy of your ancestor from hundreds of millions of years ago) is the one in charge - making your decisions and running your life. It's making those decisions based on simple emotional responses to sensory information, and its primitive little analysis of the world it's living in. The big, clever, human part of you is pretty much along for the ride - making up the story of your life after it happened. That's kinda scary, isn't it?
|Who's the boss? This thing.|
I said at the beginning of this post that I found this understanding liberating and useful. What's so liberating about having a rodent in the driver's seat of your life?
It's this: I'm no longer bound by my own irrational decisions. I'm able to recognise (sometimes with difficulty) that the choices I've made about my life haven't always been the best ones. How could they be? How can my inner weasel possibly comprehend the complexity of modern human life? If I found that I've made a bad decision along the way, I can go back and revisit it: re-evaluate the story I told myself about it, and try to come up with a better choice based on the real facts of the matter.
I picture myself taking my inner hamster out of his little wheel, giving him a little saucer of things to eat, and explaining to him why his decision was wrong. I give him a bunch of new facts that he probably didn't consider first time around. I show him some mental pictures of how things could have been if he'd acted differently. When we agree on what to do next, I put him back in his little wheel, and get on with it.
|My limbic system|
I believe that recognising the fact that your own decisions may have been bad, no matter how rational they seemed at the time, is an important revelation. Whenever possible, I try to have that little bonding moment with my Paleomammalian brain before I do anything foolish. I'd suggest that you try that too.
I've gone on about this for far too long already. But I'd like to close with one thing to keep in mind: when making a potentially important decision, try to ask yourself "What would a marmot do?"