Saturday, February 7, 2015

Genetic and Environmental Factors of Individual Brain Development


Genetic and Environmental Factors
of Individual Brain Development







A sharp reader of this blog when reading the previous post on Evolution, Life, and How Our Brains Developed picked up what is going to be a major theme that will run through this blog (or book) – compassion, and particularly self-compassion.

As we saw in the previous chapter, our brains are the result of millions of years of “R&D” (AKA evolutionary trial and error and development). So when we look at the neuronal package that we modern humans have, we certainly can't take any credit for what any of that long process put into our own modern brains. This also means, more importantly, that we cannot blame ourselves for what's in our own brains or what might go on in there at any given point of our lives. And as we learn in this chapter some of the factors that went into forming your brain, we'll see that we certainly can not blame ourselves for what's going on or been going on in ourselves when we're suffering through some sort of psychiatric or mood disorder difficulty.

Understanding how our individual brains developed starting from conception through to the present is, in my view, extremely important for two reasons; one, is to start building a better perspective and understanding of what renowned neuroscientist Robert Sapolsky calls "individual differences" or another concept that is gaining wider recognition and acceptance, that of "neurodiversity", both of which stress not only not judging those whose behaviours, characteristics and traits are "different", but also promoting a more objective understanding for how and why they are the way they are.

Secondly – and a major goal of this blog – to create a better understanding of "self" for those who are suffering from some sort of mental health disorder or difficulty in order to help work past the self-blame, self-hate and general negative self-image that is so common among us with moderate to severe disorders. For we're going to see that that nobody – that would be zero people – have any choice or input whatsoever over “who they are”. Not you, not the greatest, most successful people, not the comfortably well off middle class person, not the “rugged individual” who “thinks” they “made it on his/her own”, not the homeless person who at this moment is lying in a street fighting off cold, starvation and societal hatred while battling a severe psychiatric condition. Nobody.

Considering the mountains of material available on this subject, this is going to seem very rough and brief. My hope, however, is that will suffice for now to give us a basic understanding of some of the factors that go into creating a given individual - and of course how you came about.

Who and what you are (or who or what any individual is) is a product of your (or his/her) brain. Any individual trait, characteristic, ability, skill, mental strength or weakness, strength or weakness of character, intelligence, innate instincts, emotional responses, capacity for love or hate, morality - every single aspect about us and who and what we are – is a product of how our individual brains are arranged. If we think back on Neuroanatomy 101 (and it is at times like this that my wish is for readers to use that chapter for reference purposes) and the astronomical amounts of neurons, connections between them and hundreds of specialized regions that control this or that not to mention over a hundred different neurochemicals and hormones that roar around in there, everything about “who we are” is determined by how all that “stuff” gets and remains arranged. 

Since first writing and publishing this a few years back I've been involved in numerous discussions on this with various people from which I've been able to make a couple of observations.

One is that many people want to apply what I'm saying here to having more compassion for themselves and what's gone wrong in their lives and why. Which is great, of course. This is a massive point of this blog - to help people understand themselves and their minds and all the things they don't like about themselves or their lives and to get past the self blame and hate. The other major point of this blog, however, is to create this same understanding and compassion for others. So while it's fantastic that many readers have learned self-compassion and forgiveness and thus have been able to work past the hideous soul destroying burden of self-hate and gnawing guilt and self-blame, it's my great hope that readers learn to apply this same understanding to all people, even - nay, especially - people we find ourselves hating, violently disagreeing with and so on. You know, the "others", the "thems" (of "us" vs "them" fame). 

This too is vital for learning to let go of all the emotions that are so toxic for the mind and body. I must therefore ask you to better bear in mind the lessons we learn here when being tempted to judge others. Remember, whatever it is you feel is "wrong" about those people came about by this same process – factors for the ost part outside of their control. 

Two, there are large numbers of people who have very great difficulty accepting that they didn't have control over creating "who they are" and that they are "who they are" due to the circumstances and factors briefly outlined below. There is a strong need for many to have this sense of "agency" over everything they are and do. While this is understandable (and an enormous philosophical quagmire), this belief becomes a very difficult stumbling block in understanding human behaviour and, as is the focus of this blog, mental health disorders and how to understand and treat them. This mindset is a significant part of many's belief that those suffering mental health difficulties or with long term mental health disorders or difficult behavioural issues should just be able to change at will.

So this is another point I need people to learn, take away and apply from what we learn here (and to learn more along these lines).

With these thoughts firmly in mind, let's get down to looking at what does arrange this thing between our ears that creates "who we are".

The short answer is genetics and as we saw in the previous chapter, a great deal of what's in our brains is determined by some very old and ancient genetic development (AKA evolution). Many of our behaviour driving brain mechanisms, inborn instincts and “programming” (we're going to look at these in more detail in a future chapter) are very old and were “developed” for times that bear virtually no resemblance to our present world and environment and societal demands. Yet there they still are. These are very standard among all of us (though the very factors we're going to look at here could possibly mean that some key components are missing or defective). In other words, there is (relatively) standard DNA code that gives our brains “standard equipment”, just as it does our bodies with basic equipment such as two arms, hands, legs, feet, sexual organs (and much so on).

But just as all our physical bodies differ, so do our brains. And just as all our bodies perform differently, so do our brains.

No other species varies as much as homo sapiens do. Now, we saw in the previous chapter that we share 98% of our DNA with other primate species and 99.9% of our DNA with all other humans on earth. Yes, there's only 0.1% difference between you and – for example – an Amazon bush tribesperson or the most brilliant scientist or composer or, for that matter, the most heinous psychopath locked up in prison. Many of us have family members – offspring of the same lineage of parents and family heritage – who often make us wonder if we're from the same planet, let alone the same parents (I even think this about my identical twin sometimes!). And of course we have massive political battles about the differences between the sexes. But as I've said, the devil is in the details so lets (finally) have a look at what varies our individual genetic codes and of course the enormous environmental factors that go in to producing such different and widely varying versions of “us”.

Let's assume that we're going to have a standard biological birth; that is, it's the result of a male and female sexual coupling that successfully resulted in one of the millions of the man's sperm finding its target and fertilizing the woman's egg (IE: not artificially inseminated or a “test tube baby” (the original test tube baby turns thirty-seven this year, by the way) and so on). But to see how you got to be who and what you are we have to go back even before that successful coupling. 

Neither a male's sperm nor a female's eggs are created equal; before they even get together to copulate there are many factors that are going to affect the quality of the sperm or eggs of each. What either parent eats or what they ingest (alcohol, drugs (prescription or illicit, it makes no difference), environmental pollutants such as lead and other heavy metals and much etcetera) is going to affect the quality of sperm or the egg. Numerous, numerous studies now bear this out. One study that I came across showed how cocaine use by the father alters his sperm making his offspring more prone to cocaine addiction (in the book version of this chapter I'll include more details of these studies and supply citations, and I'll try to update this post in the future to include links).

And as I alluded to in the previous chapter, the stress each parent is experiencing prior to and during copulation attempts is going to affect their sperm or eggs as well, something we'll look at in more detail in the chapters on stress.

So right off the bat, in any one coupling between the same two sexual partners and the eggs of the female and the sperm of the male are going to be slightly different in quality each time and thus the DNA coding within each slightly different (the Chinese have understood for as long as a thousand years that diet, health and lifestyle affects conception and have acted accordingly when trying to conceive, eating special diets, keeping the female as stress free as possible, etc). In other words, before you are even conceived things are going on that are going to effect your particular batch of DNA and thus who and what you are going to be!

Moving now past the point of successful copulation, let's now look at a bit of what happens once that one lucky successful sperm has fertilized that egg. Now this is where the true miracle of life begins, the miracle that created “you”.

By “miracle” I don't, to be clear, mean “miracle” in the religious “God's work is a miracle” way. No, the natural world is full of miracles that are wondrous in their own ways and it is science that has shone the light on the details of the miracles of life all throughout the natural world. A single human birth is miraculous enough but no more so than, say, a fly larva metamorphosing into an adult fly or a caterpillar into a butterfly or the long slow process of an acorn becoming a mighty oak or countless similar examples. They're all equally miraculous and all equally amazingly beautiful to behold. All of nature is a miracle and human birth is just one tiny example.

So, you've been conceived and now cells are furiously dividing, forming and scooting around while forming “you”. We're probably all by now familiar with breathtaking images of the fetus's body forming in the womb. Fascinating to be sure but that is minor compared to what those images cannot show – the formation of the brain within. And this is where a good part of the rubber meets the road in creating “you”.

The process looks roughly like this:




Now here's where it gets interesting as far as individual brain development goes.


The average adult brain contains roughly 86 billion neurons and a normally developed baby's brain will contain about the same number at birth. Starting by the fourteenth day after the egg has been fertilized, the neurogenesis process will produce neurons in the developing fetus during a full nine month term at an average rate of roughly 250,000 neurons per minute. Yesseree Bob, 250,000 neurons per minute for nine months (4)At the peak of neurogenesis, up until about half way through gestation, neurons are being created at an astonishing rate of 500,000 neurons per minute.


But that is not even the most astonishing - or miraculous if we will - part. Then - then! - all those neurons have to migrate from the point of generation and assemble themselves in precisely the right spot plus form the right kind of neuron. A neuron migrating from the point of neurogenesis to its final destination in the brain has been likened to a baby crawling from Manhattan to Seattle and arriving not only in the right neighbourhood, but on the exact right street and exact right address it was destined to from Manhattan. To get there, the "baby neurons" follow a sort of cerebral highway laid down by cells called radial glia which itself has to go all swimmingly well in order to guide the neurons to their proper destinations.


And all kinds of things that go on in the womb and what is carried through the umbilical cord or that may pass through the placenta during that time has the potential to affect that process, as recent studies into the effects of environmental toxins have shown not to mention the effects of alcohol and virtually any substance be it legal prescription drugs or so called street drugs or perhaps ingredients contained in many processed foods. 

Further on environmental factors and brain development, it is well understood that small variations in the mother's thyroid functioning can negatively effect the fetus's brain development. Growing amounts of research has demonstrated that chemicals found in everyday household products can disrupt thyroid functioning and hormone levels key to various aspects of 
fetal brain development.

Or genetic mutations from both or either parent may affect the process. A genetic mutation or a passed on mutated gene may, as just one of hundreds of possible examples, affect how neurons migrate to and take form in the Broca's and Wernicke's areas (the parts of our brain responsible for speech and language processing) or perhaps something went amiss on the that "cerebral highway" and the right amount of cells did not arrive in the right places and as a result a person may be left with an incurable inability to process or form certain aspects of grammar (Steven Pinker's 
The Language Instinct).  


And it is groups of these neurons that form all processing regions of the brain. So just what goes on during our fetal development can affect "who we are", even with identical twins. Yes, even in the same womb each twin will experience that environment slightly differently leading to slightly different brain development (they each have their own umbilical cord, for starters). 


Back to genetics for a moment, the stress the mother experiences all through pregnancy has the potential to "switch" genes on or off or otherwise affect DNA expression. As just one many possible examples, a massive recent study done in Europe establishes with almost complete certainty that homosexuality is a product of the stress the mother was under during pregnancy (and/or likely during conception as well). Stress hormones are now known to be a major component that "switches" DNA this way or that and, it appears, may (but only may) alter the genes that regulate sexuality and related brain development (certain areas of the brains of homosexual people are different than those of heterosexual people). (1)


Also in the environment of the womb, a great deal of recent research has shown that there is a good chance that maternal immune response can affect fetal brain development possibly leading to disorders along the spectrum of autism and schizophrenia. 


As we saw in Neuroanatomy 101, neurons "encode stuff" (remember the "Jen neuron"?!). But whatever stuff a given neuron is entrusted with encoding (or whether it gets encoded in the first place), it's not particularly useful if it can't pass its specific encoding task on to other neurons to assemble mental images, thoughts and many, many other tasks from the mundane (like mastering crawling and then becoming an upright human) to the critical (decoding all those sounds coming from people's mouths into language, and then generating responses to that and countless other tasks of learning). That's a process, you'll recall, that entails the "wiring". 


Once neurons complete their dizzying complex journey to where they must "set up shop", they begin to undergo an even more complex and vital procedure. During their journey, they are little more than a little sack of cytoplasm. After reaching their final destination, they start to sprout frizzy little outgrowths that will become dendrites and axons. While dendrites are relatively short, the axons must reach out and create critical "long distance" connections and thus create your "connectome", the "wiring harness" we looked at back in Neuroanatomy 101. To remind you, in the adult brain it looks something like this set of breathtaking images.






As the fetus's brain is frenziedly creating neurons and sending them off to far flung destinations around the brain, all the main connections between them must form and the axons' journeys through the fabulously complex and chaotic "construction zone" of our developing brains is just as miraculous as we just saw with that of the individual neurons'. 


All these axons must form critical bundles that will become our main "communication lines". This is what's referred to as "white matter". These axon bundles, this white matter, will play massively important roles in our basic functions - all our senses, stress response systems, procedural and cognitive networks and much etcetera - and all the higher cognitive functions that allow us to learn and do all the skills that make us human, from language and mathematics to being able to make predictive guesses and recall past events at conscious will and much so on. 


What makes these axon bundles appear white is the myelin sheath or "insulation" that coats much of most axons. This coating itself is critical to optimal signaling between neuronal groups. 









Recent research has shown that "laying down" this myelin coating is vastly more complex than previously thought. This process of axons growing and connecting brain regions and this vital myelination is also going to be influenced by environmental conditions when still in the womb and throughout childhood and early adulthood. Neuroscience research of the past few decades and especially of the last several years has proven that environment and nurture hugely affects how our brains form (3)). 




[I was greatly pleased to recently learn (as of November of 2015) that a great and important project is underway to start mapping and logging the connectomes of newborns and throughout their young developing lives. This is a project that will give us enormous insight into what makes "us" in our earliest environments. I find it incredibly exciting. Here is a brief outline of this project. ]


And remember the synaptic connections we looked at in Neuroanatomy 101? These are the microscopically small connections where the "hand off" of information is passed on from neuron to neuron (to create everything from vision and sound to all thoughts, memories, skills and so on). These too are absolutely vital and must be created throughout the fetus's development. You'll recall that the average adult brain has in the neighbourhood of one hundred and fifty trillion synaptic connections, which means that there is a whole lot of "connecting" going on in the developing fetus's brain. When you were around seven months old in the womb, new synapses were forming at the rate of forty thousand per second.




And once a baby is out of the womb and into the world, the action does not stop and there are frantic and enormous amounts of activity in the very young brain, a process that looks like thus:






That is from the neocortex, as we can see from the six layers we looked at briefly in Neuroanatomy 101, and what we're seeing is the rapidly expanding networks of dendrites and axons. Environmental conditions HUGELY affect this process. Environmental richness stimulates and promotes more and better connections, an environment poor in enrichment and proper stimulation less so. And this environment starts in the womb. The connections you see will greatly, greatly affect what a newborn can do and how well for it is not only the number of connections but how they're connected and with "whom else" (IE: which other neurons) that is very important and relevant. And now numerous studies are showing how the stress of poverty at this early age can negatively alter brain development. 


But it doesn't stop there.


Early life nurture and environmental conditions will have a huge affect as well as we can see in this image:






All of these connections and how well they form and connect with and among other neurons or not is highly subject to environmental stimulation and input as well. You'll see that the connections get less dense as we enter our teen years in a process known as "pruning", during which time many of the connections your young brain furiously created are deemed as "unimportant" and get pruned back. What the brain determines as "unimportant" during this phase and what does or doesn't get pruned is also critically dependent on environmental and nurturing conditions and thus will also hugely determine "who you are". 


And it still doesn't end there!


There are two periods in our brain development known as "critical periods". The first one takes place during the toddler years, approximately from age two to four, in which the brain undergoes massive reorganization. You see, we are not born with all the brain regions we'll have at adulthood, nor is what we're born with fully developed. It is during this first critical period that the brain must receive certain stimulation for this reorganization to go optimally and/or for certain regions to form properly at all. Language abilities and the ability to bond with others are just two aspects of development that are greatly affected during this first critical period. There are aspects of our "humanness" that if they don't develop properly during this period, it is highly unlikely they will ever properly develop. Ever. (2)


The second takes place during our latter teen years and in to our early twenties when again the brain undergoes massive reorganization, especially in the frontal lobes where all our "adultness" (AKA "maturity") is contained, such as the ability to focus, make judgments, regulate moods and so on. Again, what our environments are like is going to hugely affect the brain during this crucial, crucial period of development. Again, if these key regions don't "come on line" during this period, there is a good chance they will never fully develop properly. This second critical period won't quite "set in stone" brain regions like the infant stage will, but very close to it. 




What we looked at here is just the elementary basics. There are literally dozens of microscopic details that also affect brain operation the development of which are also affected all throughout our lives from conception to birth to death (but particularly during our earlier critical years). 


I think we can now see that the idea that anyone has any kind of "control" or "choice" over how all this develops is simply ludicrous (and you can officially classify anyone who still argues that nurture (of nature vs nurture fame) isn't important to your/our mental and emotional development as an imbecile). 


All of this is going to be enormously affected by the quality of our parenting, sibling interaction (if any), early education, whether we have exposure to music or learning an instrument, second languages, whether we play sports or not, how we play and interact with other children and almost countless other factors. Recent research has shown how childhood adversity can affect the development of grey matter in adolescents.
Many environmental influences on young brain development of this kind is becoming much, much better understood with recent research. 


So, back to the points I wanted to make clear at the beginning and the take-away points for this chapter:


People whose lives go all swimmingly and who consider themselves "brilliant", "well adjusted", "emotionally mature" or any of the other countless things that people feel so smug about themselves had practically zero control over becoming that way. They are what they are because all of a) genetic factors they were blessed with (and nobody, I think we can all easily agree, "picks" their parents and contributing DNA) and b) the ridiculously complicated above processes all went well. I'm going to pick apart the notion of "free will" and "self-determination" in a future post but I can assure you for now, nobody controls "who they are" or even what they do. NOBODY. 


What I'd really like everyone to take away from this post and what we've learned here is that the process described here is what forms every human being. Whatever differences we have, wherever we fit on the scale of mentally "healthy" or of morality or whatever state a person may find him or herself in, it was a product of this process. In other words, we're ALL formed by this process and as such no one person can judge any other one person. But I have much more to say on this in future pieces. For now though, I wish everyone could get past the tsk-tsk judging of others and their struggles.


More importantly, and a core theme of this blog, is that if you are undergoing any kind of mood disorder or psychiatric condition, do NOT blame yourself. You had absolutely NO control or input into that happening. 


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3 comments:

  1. I was fortunate to have studied childhood development, nutrition and psychology before having a child. That made me do all I could to give my child a good start. Unfortunately I picked a poor partner, so half of what I did went out the window. Choose your partner wisely if you want well adjusted children, is my advice. Thankfully there is some hope even later in life. Thank you Brad for this informative post.

    ReplyDelete
    Replies
    1. I agree with Trudy...choose your partner well. Maybe similarity in reasoning and understanding one another is the biggest key in healthy relationships.

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  2. Almost all human beings have problems caused by genetic or environmental factors and or both. Therefore, a deep compassion is necessary for the human race. ...

    ReplyDelete