Sunday, November 10, 2013

Neuroscience 101

Neuroscience 101:


    This will be a very basic primer into the physiological systems that makes a brain - IE: "you" - tick. It will seem quite lengthy, for which I apologize, but there is a lot to get to. Human behaviour is, as I briefly demonstrated in the previous post, extremely varied and complex, not to mention seemingly incomprehensible, and if we are to begin better understanding our complex selves - or even our simple selves - it is basic brain functions as understood by current neuroscience that we need to better understand and be aware of. It is my hope that this post - and following posts that will explore these basics in more detail - will serve as a) a reference for us to refer back to as we go along, b) a reference for your future use and more importantly, c) an impetus and inspiration for further curiosity and reading on your part (if not, I will be doing my best to provide as comprehensive an understanding as possible in the easiest way for us layman to utilize). 

    So here we go, let's dive in.


     First of all, you have in the neighbourhood of one hundred billion of these:


    That's a neuron and according to renowned neuroscientist David Eagleman, each one - all one hundred billion of 'em - is as complicated as a major city (there's an astonishing level of activity that happens in all of your cells, it's just that brain cells take that to a new level). Neurons "encode" stuff. The details of all your thoughts, memories and all your knowledge are encoded in various neurons (for example, there's a "Jennifer Aniston neuron". Honest! The discovery of this is detailed in neuroscientist Sebastian Sueng's book, The Connectome. Whether you have a "Jen neuron" or not depends, of course, on whether you've seen her or not and whether a certain other brain region has "decided" if this person is important to you or not). They pass that encoded stuff (to assemble bigger pictures or ideas or memories) along to other neurons via these:


    Those are axons (sending) and dendrites (receiving), AKA "the wiring" (though technically more the former than the latter). While brain cells are more or less permanent, the wiring is not. (By the way, contrary to popular belief, you do not "lose" brain cells ... no, not even after a bad bender, but yes, it can feel like that. And we're going to look in much detail at what happens when you abuse that poor brain of yours by consuming various substances, or "food" for that matter, and why it "feels" like we lose brain cells. It won't be pretty). Axons, dendrites and synaptic connections grow and "prune back" all the time, creating new connections (and thus memories, learned behaviour and the such) or trimming them back (if a certain memory function falls into disuse for example). As you can see by the number of dendrites, there are many, many connections between neurons (as many as ten thousand according to some counts!). Dendrites and these multiple, multiple connections are a big part of our mental puzzle. A more realistic depiction of what these connections look like appears like this:






    That bright green blob in the centre of the image is a neuron. Yup, you've got one hundred billion of those, each one with enough activity within it to be compared to a major city. Imagine the activity of one hundred billion cities going on in your brain (though not exactly all at once - more later). 

    Communication between neurons is sent along the axons in electrical pulses not unlike Morse code. At the point of connection between an axon and a dendrite we have a synapse and at this point the electrical pulse triggers the release of a neurochemical which will pass the message from axon to dendrite and thus onto the next neuron. The details of this transfer, and the synapse itself, look something like this:


    This happens to be for the system involving the neurotransmitter dopamine. You may notice opiate receptors as well, along with endorphins. We'll be coming back to opiates and the brain later. As you can see, there's a lot going on there. There are receptors, "uptake pumps", there's a system - not shown - for whisking away excess neurotransmitter material and so on. This operates on a ridiculously delicate balance (we're going to come back and examine this in more detail in a future post). There are something like one hundred known neurotransmitters, all of which perform inter-neuron communication in various regions of the brain and all of which are responsible for various functions that drive "you". Look again at that tiny detail (and you may recall that it was a description of the function of a synaptic connection that first drew me into neuroscience). Much of who you are and what you do depends on that infinitesimally small chemical transaction. Now get this; your brain has somewhere around one hundred and fifty trillion synaptic connections at any one time all performing those little chemical transactions. And to put that number in perspective, in just a few cubic centimeters of cortical tissue you have more synaptic connections than there are stars in the Milky Way (David Eagleman's Incognito). Now stop reading. Stop and really imagine - again imagine those hundred billion cities between your ears. Now imagine enough transportation connections between them that the numbers dwarf several major galaxies. Yeah, I know, pretty awe inspiring. And quite beyond the capacity of the imagination of most of us. 

    The dopamine system and pathways happen to be one of the most studied and well understood. The dopamine pathway looks roughly (and I do mean roughly) like this:


    As you can see, the seat of our emotions, a small part of the brain called the amygdala, is included in the loop. And hey-ho, what's this? Our "planning and judgement" centre is a destination? Yuppers. A lot of what you "think" is "good planning and judgement" may well be just your primitive brain reward system sending an emotion generated "good feeling" message to your "command centre". And this diagram just represents the dopamine pathway. Remember, there are over a hundred different neurotransmitters at work throughout your brain all governing - way below your conscious control - various functions going on in all those billions of cities in your brain. 

    Let's return to the "wiring". There's "local" and "long distance" wiring. Local wiring in the mammalian neocortex looks something like this (and this is a greatly simplified drawing). It works in layers and each layer performs a slightly different level of function (from Sebastian Seung's The Connectome). 



    Long distance wiring is longer axons that form "bundles". This wiring connects the different brain regions. It is believed by some neuroscientists, such as Sebastian Seung (linked to above), that it is the unique wiring we each have between our brain regions - or "connectome" - that is responsible for much of "who we are". A basic "wiring harness" looks something like this:



    The brain and its wiring is not, as once thought, "set" once full neurological adulthood is reached (about age 25). As mentioned, axons and dendrites grow and prune back depending on the demands, or lack of them, put on a region at any one time. This falls under the general heading of neuroplasticity, a term that describes the malleability and changeability of our finest (and we're talking very fine) and even major brain structures. We'll come back to this important concept in much more detail in future posts but right now it's important to know that this plasticity can be good (the brain changing to adapt to a major change such as blindness) or bad (adapting to a harmful behaviour or practice (brought on usually through negative experiences or environmental conditions)). And that wiring? You have, in that small space between your ears, enough wiring to wrap around the world - twice. 

    But the wiring does not end there. The wiring includes the central nervous system and connects every square centimeter of your body to your brain, something like this:



and this:






    These are not only to send messages to muscles to move and to receive information in return or to receive and send pain signals (and we'll learn that this is a two way street) but are also part of a "full systems" monitoring program that is constantly testing what's going on in, as the latter diagram shows, your major organs. We'll be examining this in more detail as well when we learn more about the mind-body connection and how, for example, what goes on in your stomach may affect your mental health. For that matter, what goes on anywhere in your body is going to affect your brain in some way.

    Aside from neurotransmitters, there are also hormones involved, such as the stress hormone cortisol. Its pathway looks something like this:


    The stress response system is based on our primitive brain "fight or flight" response to perceived danger (and the term "perceived" is very pertinent here. How we perceive danger is one of the things that gets out of wack in our brains outside of our conscious control. Phobias fall under this category, among many others). This system is essential to our survival and we'll explore this crucial system in more detail later but what's important to understand now is that this system evolved for fairly simple dangers like a saber-toothed tiger eyeing you for dinner. In our modern wacky world the concept of "danger" and our response to that is way, way more complicated and this system is often put under extreme duress. We'll be returning to this a LOT as we try to understand this system's effect on our behaviour and physical and mental health.

    There are of course numerous hormones that greatly influence our behaviours and "who we are". Some are quite familiar to most of you - testosterone and estrogen for example - but we'll look at others as well and more importantly look at better understanding the roles these play in what we do and why we do them (or not do certain things). 

     And in among all those neurons and wiring are glia cells. Neuroscience is just scratching the surface of the essential roles these play. One critical role is in supporting the growth of the myelin sheath, a protective coating on axons (the breakdown of myelin is thought to play a role in MS). As well, they are involved in supplying nutrients and oxygen to neurons along with various "clean up" duties. Recent research suggests that among the reasons we need to sleep is that glia cells need the brain to be in a resting state for them to perform many of their functions (most critically, it appears, the essential house cleaning duties they perform). Glia cells look something like this:



    Isn't this just the funnest stuff?! I love this stuff! Let's carry on. 

    Reptile brains, then higher brains followed by the mammalian brain, then the early hominid brains and finally the modern human brain evolved over millions of years. Each was basically bootstrapped off of the more crude and ancient reptilian brain. (Yes, I know how sophisticated you think you are, but at your core you are exactly the same as your average frog.) The limbic system evolved next and then, as mammals came on the scene, the neocortex evolved (or mammals came on the scene as the neocortex evolved I suppose). Thus our basic brain outline looks like this:


    That big reptilian brain blob at the back of the brain is the cerebellum. That's where body movements are coordinated, where your abilities of balance and body posture are held and equilibrium is controlled (yup, the most graceful ballet dancer or gymnast in the world shares the basic hardware responsible for what they do with a lizard). If you're not super graceful, blame this region, not yourself. The limbic system is where a number of major control centres reside, including, but not limited to, the aforementioned amygdala, the hypothalamus (the control centre for many autonomic functions), the hippocampus (involved in memory forming, organization and storing) and the basal ganglia (or basal nuclei; involved with a variety of functions, including voluntary motor control, procedural learning related to routine behaviours or "habits" such as bruxism, eye movements, cognitive and emotional functions).

    Finally, we have the neocortex. This is divided into major regions that look something like this:



    If you'd like to know where "you" are - the seat of human consciousness and awareness - that's in the frontal lobe. We'll have much fun examining how much - or how little, perhaps I should say - that part runs your life. And do you see that part called the occipital lobe? That's where you "see". Our eyes merely collect light. That live action movie that takes place when you open your eyes gets produced, edited (yes, whatever you may think, a lot of editing takes place of what your eyes take in) and assembled in your occipital lobe and which then presents the final cut to "you". 

    The neocortex is where the responsibilities of our higher functions lie. The neocortex is divided into a dizzying array of specialized functions. This is a short list but all areas of thought and cognitive functions will have a corresponding brain region that looks roughly (and again, I do mean roughly) like this:


    These represent just a small handful of examples and are only roughly located in this diagram as the areas are presently understood (neuroscience is making new discoveries all the time so none of the exact specifics of these locations are set in stone but the basics are well understood and agreed upon). How "good" you are at any particular activity will basically depend on a) how well developed a particular region is (say the Brodmann and Wernicke areas of language, for example (roughly "speech production" on the chart) or something more rudimentary like your cerebellum as we saw), b) how well the wiring is developed between your regions and c) how your particular neurochemical pathways perform. It's somewhat more complicated than this but these three are well understood to be the basic components. I earlier compared a graceful ballet dancer or gymnast to a lizard. It is in the neocortex where we can find the answers as to why the former can take the same basic muscle-skeletal system and brain component - the cerebellum - and perform quite a bit more complex body movements with them. Or why any mammal can physically outperform a lizard for that matter. There are of course some physical differences between, for example, a chimp and a gecko, but most of the reasons involve the differences in brain structures between them, the most important being that a chimp has a neocortex and the lizard does not. That you have the most evolved neocortex on the planet is also why you're more sophisticated - most of the time we'd hope - than a frog (to which I also compared you). But, well, we'll see. When we really start comparing you to a frog (or any of the other creatures with which we share basic brain hardware and functions) you're going to find it quite humbling. 

    That our brain regions and the connections between them are all different puts a whole new meaning on "smart" or "talented". "Smart" or "talented" is just a blessing of various regions being better proportioned and wired for a given task and you accidentally discovering the use of these regions (or more likely having them discovered for you). If you're a math "genius" and make a living from that, for example, you can climb down off your high horse and thank your lucky stars that you were gifted (and we'll see what "gifted" really means ... nothing to do with "you" I can assure you) with highly developed regions specific to math tasks (nature) and that they were discovered and developed (nurture, which strengthens the connections, or wiring, between these regions and the rest of your brain). Many people may be similarly gifted but tragically never discover these gifts (and we'll see that undiscovered geniuses may be at this very moment living in the slums, for just one example, of Lagos, Nigeria). Others may not be so gifted but are cursed with high desire (or being driven by well meaning but ill-advised parents) and thus tragically beat their heads against the wall (and beat up on themselves) trying to do something they were simply not endowed to do.

    All of this, the billions of neurons, the trillions of synapses, the dozens and dozens of specific brain regions, the hundreds of thousands of kilometres of wiring that tie it all together and the more than one hundred neurotransmitters, hormones and proteins that make it all communicate, harmonize to make up this - your brain:



   The brain from any healthy adult will look like the one pictured above but here's something to consider, and is the essential foundation to what we will learn about brains - no two brains are alike. They are as unique as fingerprints. All those regions are connected slightly differently between us as well as some regions being better developed or activated and some not so much (which can be long term or short term), the wiring is slightly different between us and so on. This is, as I've pointed out, determined by genetics and environmental factors, with a strong emphasis on environmental factors. Even identical twins (of which I am one) who start out genetically identical will develop quite different brains (as a twin myself, and because twin studies are so fascinating, we'll be returning to twin studies quite often).

    The brain collects "data" through the five senses (sight, sound, taste, touch and smell), runs this data through various brain regions and creates the "reality" we perceive in our minds. Because our sensory organs and brains are all genetically different (with the exception of twins) plus are wired and developed slightly differently, we will all have different "versions" of "reality". This is why we find it hard to agree even when we're both looking at the exact same thing (like two people seeing a spider for example. One may look on with fascination and curiosity, the other will have a phobic melt down).




    This is going to be a critical part of our examination of human nature and the brain. Remember how I said we needed to better understand brains if we as people were going to better learn to co-exist and cooperate with each other? Obviously our differing views of realities - and we have very, very little conscious input into what these are (or exercise very little as we'll see) - are major sticking points. "Reality" is one of the great philosophical questions of all time and, as it turns out, crucial to understanding the human brain and our inward and outward "selves" and, most importantly, how all our widely varying "selves" get along with other "selves". It is, as the Chinese say, quite "複雜 " (complex). We'll be examining this a lot and how we might better agree on "reality" (hint - science).

    All this stuff is what's "under the hood" of our skulls. And this three pound collection of cells and wiring is, as any neuroscientist will tell you, the most complicated device in the known universe. When human behaviour goes wrong, there's something wrong - emphasis on something - "in there" ::waves a hand in the direction of all the diagrams outlining the ridiculously complex human brain::.  All that varying behaviour we looked at in the previous post can all be explained by understanding all that ::again waves a hand at all the brain basics we just looked at:: That's it - nothing mythical, nothing otherworldly, just how all those things are arranged in each of us. And here's the kicker; even neuroscientists will admit they don't understand the brain very well. And they don't. Neuroscience, like astronomy (and they aren't that different in terms of vastness and complexity), is very much a work in progress. We can study deceased human brains, but it's exceedingly difficult to study live human brains with instruments. This is why so much neuroscientific study takes place on animal brains (many systems are similar between us and animals, remember, so discoveries on mammal brains can be to some degree extrapolated up to the human level. Even neuron and axon structure on something as simple as a round worm are essentially the same as ours (and so form a basis for neuroscientific study). Human psychology is far more complex however (and this will entail a great deal of our exploration). Advanced neuroimaging technology is helping to a large degree in our study of brains and individual personalities and characteristics contained within them (and there's the technology that can even probe an individual neuron and detect that it only activates when presented with an image of Jennifer Aniston (as one example) and thus the "Jen neuron"). While great advancements have been made on the details (as exemplified by those breathtaking diagrams of neurons and synapses), how it all comes together and creates a "you" remains at least somewhat mysterious (or a lot mysterious, depending on one's confidence in today's theories and knowledge (knowledge that is changing all the time)). 

    And here's the big take away for today. All of that "stuff" runs a mind boggling number of subconscious "programs", what Eagleman calls "zombie programs" and it's your particular collection of zombie programs (we all vary in these though some are quite standard) that run "you". No, "you" don't run "you", all these automated zombie programs - programs that run through all those neurons, wiring via electrical pulses, neurochemicals and hormones (to put it very basically) - run "you". Zombie programs are all your daily routines that you don't need to think about in addition to all kinds of other little programs that push you forward through life. All those "conscious decisions" you make are almost certainly to be the result of various zombie programs spitting out, for example, the "decision" to buy a new car (which is just a glorified modern variation on ancient hunter-gatherer instincts) or take a new night class or pick a certain supermarket product over the others and so on. Then your dopamine reward centre gives you a "hit" of happy feeling dopamine to "reward" and "re-enforce" this behaviour. These are going to be a huge part of our exploration of what makes humans tick (or even your cat or dog if you like!).


    Phew! Wasn't that fun?! And that was just the very basics. In future posts we'll look at all these parts in more detail. We could think of all these parts as pieces of a puzzle that we are putting together. The completed puzzle is a biological computer of such dazzling complexity that human language is inadequate to completely describe it. For every second of every moment you are alive, your biological computer - your brain - will be performing an astounding number of functions, virtually all of which are outside of your conscious awareness, let alone control. In fact, as I've already alluded, we will see how astonishingly little control we have over who we are and what we do (though once we understand why that is it'll be far less astonishing and the only way we could possibly operate and get through life). 

    But perhaps more importantly, we'll learn more about just what kind of control we do have. And isn't that something we'd all like to know more about? But more than that, the answers to all the questions we looked at in the previous post can be found by better understanding how these amazing biological computers of ours operate.

Oh, and I hope you now better understand the meaning of "inner galaxies" in the title of this blog - you truly do have vast inner galaxies in your brain. Now is that cool or what. 

1 comment:

  1. Have to save this for later Brad and loved the first image! I will read over the weekend!

    ReplyDelete