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Continuing from the ending question of Part I: what makes us all really tick?

Let's start by internalizing how important the brain is to us human-folk: a whopping 60% of the body's glucose goes to the brain. Gram for gram the brain eats ten times more calories than does the body as a whole (20-25% consumption for only 2% of body mass) For an organism that evolved not knowing when or where it's next meal was coming, that big eater had better be good for something. Aristotle, who my history teacher thought was just the smartest man in history, blithely asserted that the brain must be a cooling engine for the body. (I like to kid Aristotle for just pulling stuff out of his ass like that. Bertrand Russel had some good zingers on him too. But I digress)  Anyway,  consensus neuroscience opinion these days is a little bit different. It seems to be the brain has basically two jobs (which we'll see in a sec is really the same job): 1) control motor function 2) predict the future

Controlling motor function is almost obvious as soon as you think about it: really it's the only way the organism can affect its environment. One prime exhibit often cited for the rule "brain = locomotion" is the sea squirt, which will actually eats its own brain once it settles down to a sedentary life on a coral reef. But like John Lennon might have said, life is what happens while biologists make other theories: note the humble jelly fish and even slime molds seem to purposefully navigate their surroundings quite well without any central nervous system thank you very much. Sorry, digressing again. Either way, it's clear that at least our brain controls motor function. 

But think about what a gargantuan task that is. First of all, just counting the 650 skeletal muscles in the human body (ignoring cardiac and smooth muscle tissue) presents the brain with 2 to the 650th power, or roughly 5 followed by 195 zeros(!), different possible motion states to control.* How can the brain possibly choose the few right needles among that astronomical haystack? Essentially via task 2) - predicting the future. The idea here is that the brain is constantly running internal simulations of its future possible muscle moves. Those simulations are believed to come from self-models of movement the brain creates and modifies over its lifetime. Comparing what the self-models say - i.e. what is internally predicted to happen milliseconds in the future - with the sensory feedback from the actual current motion is the basis for an extremely sophisticated control system. It's such a great system, that nature apparently said "hell, yes, let's do that!" at least as early as the Cambrian, about 500 million years ago.

Of course, those predictions will only be helpful if they contain not only the organism's own movements, but also the surrounding environment. It doesn't do an animal much good to successfully predict and then execute a move two steps to the left if that move takes it into the jaws of  a predator. So predicting the future in general - like guessing what that predator is up to as well - is another equivalent way to describe the brain's job. 

But now the brain really has a job on its hands. Try multiplying 5 followed 195 zeros times some even more ridiculously large number that represents all possible future states of your surrounding environment. Needless to say, brains don't do that. What they do though, is create and store internal models of the outside world as well. These models are kind of like look-up tables, or heuristics, built out of neural circuitry of course. So instead of actually calculating de novo what will happen next, just like in the case of motion, the brain activates a model appropriate to the sensory data; i.e. a model that will hopefully just tell it what in the world will happen next. Like is that roaring lion about to jump at me or the impala? Does she really like me or just the rabbit carcass I stole from the baby leopards? You get the idea.

But here's the funny thing: just how does your brain know there's a 'lion out there' in the first place? I mean your brain's hopefully tucked safely away inside your skull. The only thing it has access to is blood, chemical soup and electrical signals. Obviously then, it has to make its own model of a lion, because models are all it's ever going to see. "A lion chasing you up the tree" really means to your brain a model of "a lion chasing you up the tree". So the funny implication of all this is: the brain's not really predicting THE FUTURE. It's just predicting its own future; i.e. predicting the behavior of the models it creates. The brain is a self-prediction, self-modeling machine. 

Rather than John Locke's blank slate, though, we're born with at least the rough drafts of many of our models. A good and quick read on this principle is Steven Pinker's classic The Blank Slate. Newborns a few hours old seem able to recognize faces, for example, and at four months visually process those faces at almost an adult level. Toddlers less than a year old already have some sense of cause and effect of object motion, and so on. 

However much we're born with these models or develop them later, they're continuously shaped and modified throughout life by the brain reward system. The cookie in this system is the neurotransmitter dopamine. During learning to, say, play guitar (i.e. learning a model of you playing guitar), you're on a pay-as-you-go system. A cluster of specialized neurons in the mid-brain called the Ventral Tegmental Area, or VTA, releases dopamine only when the right notes are struck in the right way. Most of that dopamine lands in a nearby section called the nucleus accumbens, which also goes by the more technical name 'pleasure center'. This strengthens the neural circuits in your current model to reinforce the emergent, guitar-hero model of you. Once you get really good, though, the VTA figures your credit history is good and starts paying you up front. That is, the VTA releases the dopamine just before you hit the note - i.e. on the cue that makes your model say "OK, now gimme an F-sharp". Assuming you hit that F-sharp on time, the whole thing reinforces the predictive aspect of your model. If you're predictions keep missing the mark, though, the VTA will eventually not only revoke your credit, but stop dopamine payments altogether. That's when life can really suck, as any victim of withdrawal will tell you. 

The whole system is much more complicated, of course, with feedback loops and braking mechanisms through other brain regions like the frontal cortex (that more deliberative part of the brain that Vulcans especially like). But the point is here that your models - you - chase dopamine like investment banks chase money. The metaphor with banks is on purpose: they- and you - will even chase it to their own destruction. That's what Peter Milner and James Olds found in the 1950s when they accidentally discovered the brain reward system in mice. The accident part came when they misplaced electrodes into another mid-brain region called the medial forebrain bundle. Zapping this region with a small voltage does essentially the same job as the VTA to nucleus accumbens mentioned above. In other words, the mice felt reealll good when the juice was on. Olds and Milner then let the mice zap themselves by connecting the voltage to a small lever they could press. Needless to say, the lever became very popular with the mice. So popular that even food, water and sex were ignored when there was lever to be pressed. 

Guess the mice had never heard of Maslow's pyramid either. 
 
Next: Part III of III - how our models make us do stuff

*With the horrible oversimplification that each muscle is independently controlled to be either contracting or non-contracting.

 
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My cousin Ian and I were still impressionable pre-teens when my Dad took us to the Gettysburg Civil War battlefield. I vaguely remember passing various granite markers and spoke-wheeled canon as we strolled the uneven hills. More vivid in my memory is a tour guide explaining how General So-and-So got his head blown off by a cannon ball where I was standing. That got my attention and not in the most comfortable sort of way. It must have set the stage for me to ruminate long and hard when we got to the Cyclorama - a huge 360 degree mural painting of the battle. In particular of Pickett's Charge.

I stared at the mural and for the life of me, couldn't get my head around Pickett's Charge. As all Americans learn in school, the field the Confederate infantry had to cross that day was flat, open and long. It was basically a slow, methodical walk into a meat-grinder, and I couldn't get over the sheer stupidity of it. I wasn't thinking of Lee and Pickett so much. Commanders have to gamble, I knew, and if the thing had worked they'd only be remembered as brilliant and daring. But whether they could collectively take Cemetery Ridge or not: what on earth made those fool infantrymen line up to be artillery target practice for almost a mile? (General Trimble's estimate) At twelve, I was confident I would have shown General Pickett my middle finger or worse. Nowadays, of course, I know differently and am just thankful to be too old to take part in such nonsense. 

I'm only picking on poor Pickett (who in fairness, was opposed the charge) because it's the earliest memory I have of what used to be a great mystery to me: what on earth makes us humans tick in the first place? What really motivates us to do stuff at all? I thought the whole evolution game was about survival and having babies - where does deliberately getting your head blown off by a cannonball fit in?

If you've ever hung around marketing or psychology people, you'll have heard of Maslow's hierarchy of needs. It's a triangular shaped mini-bible with the supposed laundry list of our priorities. In reality, though, it's a list only a Vulcan from Star Trek could love, because it's so apparently rational 1) survive and have babies 2) gather food, shelter, safety 3) love and be loved 4) feel good about yourself 5) realize your dreams. Sounds so utterly reasonable until you realize it's meant to apply to real-life human beings. 

I think it's deeply ironic that Abraham Maslow published his work "A Theory of Human Motivation" in the middle of World War II, just when millions were motivated to kill and die for anything BUT the first three items on his list. In fact, if Maslow's pyramid were really true, almost nothing about human history would make any sense. Maybe Stone Age humans killed and died for sheer survival and procreation, but since then it's been pretty much abstract ideas that have driven people to that kind of behavior. During the Bronze and Iron Ages, one side was usually fighting for glory, the other for freedom. Nowadays of course, moral standards have changed, so everybody says they're fighting for only the latter. Either way, they're only fourth or fifth on Maslow's list. 

So much for survival. What about the having babies part of our supposed Number One priority? Hhmm. I guess that's why millions live and have lived in monasteries and nunneries throughout the centuries. Or why birthrates are constantly declining in the developed world. 

A lot of other not-that-uncommon behavior shouldn't even exist under the Maslow scheme. Substance abuse, anorexia, suicide - in fact any behavioral disorder that becomes debilitating enough to short-circuit items 1) - 3) on the list shouldn't be possible. But here again, in real life, 4) and 5) very often dominate. Honestly, in the face of such obvious and overwhelming counter-evidence, I severely don't get how the pyramid meme ever propagated beyond Maslow's desk. 

We've known for some time that humans are not Star Trek Vulcans carefully weighing their decisions under classic rules of rationality (say, by weighing expected cost vs. benefit). The psychologists Amos Tversky and Daniel Kahneman  worked out that kinda-shoulda-been-obvious fact in the context of economic behavior. Or maybe it wasn't that obvious - Kahneman got the 2002 Nobel in Economics for the work. (Tversky sadly died before the prize was awarded). But really, folks: it only takes a smidgen of self-awareness to know that all of our individual decisions are emotionally weighted in all kinds of directions, just not in the direction First Officer Spock would approve of.  

In fact, without emotional affect, decisions would be impossible at all, as the neuroscientist Antonio Damasio discussed at length in his book Descartes Error. After all, how else does the brain know what few bits of data out of gazillions to pay attention to? But as always, the ancient Greeks of the Axial Age were already there. Aristotle is far from my favorite Greek philosopher, but he did manage to get the point right when he wrote "There can be no knowledge without emotion". But it's not as simple as our animal instincts overriding our higher intellect either. On this I have to politely disagree with a guy who is one of my favorites, David Hume, when he wrote "Reason... is the slave of the passions." No, it's not that we're in a state of constant Pon Farr, as Spock might say. Our inner drives are vastly more complex and opaque. We should be clear that it's not about a lack of data, or even knowledge, experience or expertise that makes us so seemingly irrational (If you doubt that, I refer you to the last US Presidential election and the losing side's astonishment at the result)

So let's ditch the whole pretense that we even know what 'rational' is and whether we are even any good at it. We'll start from scratch with the original question: just what does make humans tick? 

Part II to follow.