Memory Trace Theory and What it Means to Remember

Here at the University of Texas, there's a whole department devoted to the study of learning and memory.  There is constant ongoing research regarding the subject of memory consolidation and other similar topics so we are by no means close to understanding the full processes.  However, just going over the current theory for memory caught me as a bit sad in a strange way.

Memory trace theory holds that when we first experience an event, it is recorded as a declarative memory in the hippocampus.  But with further recall (aka- reliving or remembering the event), it turns into a set of semantic information and is stored throughout the neocortex.

Your memory isn't like storage space in a computer.  It's a
constant organic process.

But memories are just memories, right?  Nope.  Our brains aren't a recorder or a photo album.  When we make the jump from declarative memories (life instances) to semantic (collection of facts), so much is lost.  We will never hold the full memory ever again.  And over time, the semantic facts we've collected can shift and change.  This explains when you and a friend tell the same story from a year ago but with very different details.

Maybe I'm excessively attached to my recollections.  As I've said before, I am the product of my memories.  My life experiences have made me who I am.  Just the past year and a half of college have given me numerous experiences that have radically altered my view of the world- some for the better and some...not. But when I realize I will never be able to keep the stories of my past unaltered by my own neural processes, I'm aware of how much I have to lose.

These are my 17 journals which I have filled with my life
experiences.  I'm currently on number 18.

I suppose it's a good thing I'm such a avid writer.  I keep a journal and every night for the past 9 years (approximately) I've written two page entries.  Sometimes they lean towards the dull side but more often than not I have a nice little story to tell.  So even if my brain can't keep the facts straight, at least I'll have these journals to serve as my window into the past.

Remember that one time when.....

How much of our personality, our soul, is composed of our memories?  I think who we are stems from what we've done and how we've learned from those actions.  But imagine an existence where you could no longer form memories.  This is the situation faced by neurological patient H.M.- now know as Henry Molaison.

Henry Molaison passed away in 2008.

Henry suffered from debilitating seizures caused by tissue in his temporal lobes.  Historically, patients before him had undergone surgery to remove the epicenter in the brain that caused the seizures and this usually solved the problem.  But for Henry, the seizures were caused by 2 epicenters- one on each temporal lobe.  So when surgeon Scoville removed the defective tissue in 27 year old Henry Molaison, he had to take large portions from both sides.

But a strange thing happened when Henry recovered from his surgery.  He was no longer able to form new memories.  Semantic information (facts and dates) from before his surgery was untouched but when it came to recalling simple episodic information (like what he had eaten for breakfast), he couldn't recall a thing.

Neuroscientists Brenda Milner and Suzanne Corkin took on the case of H.M. in the hopes of learning more about memory and its storage in the human brain.  They found that the hippocampus, which was almost completely removed, is vital for processing memories.  You could view it as a sort of clearing house where short term memory gets transferred into long term storage.  But without this structure, Henry could no longer process his memories.  In other words, he was forever stuck in the mindset of his 27 year old self.

Hi-lighted in yellow is the portion that H.M. lost.

A similar deficit was found in a Korsakoff's syndrome patient mentioned by Oliver Sacks in his book The Man Who Mistook His Wife for a Hat.  This man was also unable to form new memories, leaving him trapped in a time that has already passed.

Now while there are some technical differences on the types of memories and amount of retrieval between these patients, they both hold an amount of melancholy in my mind.  To be deprived of the ever changing world.  To be able to grow and expand.  These two men lost so much.

I am a firm believer that our genetics set the blue print but our experiences are really what make us unique. And our capacity to change is what makes us so fantastic.  My heart goes out to these two men and all who suffer from anterograde amnesia.  It's a hard world to imagine.

But what about you?  Would you rather suffer anterograde amnesia (where you can't form new memories) or retrograde amnesia (where you can't remember your past from a certain point back)?  It's no easy choice.

Body, Brain, and Mind

Note: This is actually an essay I had to write for philosophy challenging some of our neuroscience assumptions.  I know it's long so don't feel bad if you don't read it.

As a staunch neuroscience advocate, I do not like to think that there is anything we cannot discover experimentally.  The leaps made in even the past few decades have revolutionized our views of mood, personality, and consciousness.  Yet by the same token, we can never have absolute proof that the mind and all that it entails is identical to the physical organ of the brain.  My argument is that the brain functions much as any other body part, only with a much more intimate connection to the mind.  It can be influenced and changed physically and that will lead to alterations in behavior and mood.  But we have no way to control the mind completely through the brain, only to influence it as an outside factor.  Thus the correlation between mind and brain is extremely weighty, but does not serve as an identity between them.

The first case study in differentiating brain and mind comes from research revolving around lesion studies.  Lesions take place when you damage a piece of tissue so that it can no longer operate.  They often happen incidentally due to injury, but the term is usually used to refer to purposely created deficits in neural tissue.  These intentional injuries allow scientists to study what the loss-of-function for a particular region will do to overall cognition.

Just had to add this cause I love brains!

Over the years, thousands of these studies have been conducted, and while some of them have indicated localized regions involved with highly specific function, more often there are examples of the same small-sized lesions making no recordable difference at all.  Even in practical application, we cause brain damage to ourselves every time we drink alcohol or get a strong bump to the head, yet it takes a large degree of damage to actually affect a change at all.

Examining the larger deficits, such as those which plagued Phineas Gage, we still cannot say with complete certainty what the change will be. The ventromedial prefrontal cortex which Gage destroyed with his tamping iron is involved in decision making.  This much we can state as fact.  But the loss of function does not mean that he used to pick B over A but now he will always chose A instead of B.  The effects are highly convoluted with only a general pattern to guide us.

But an opponent to this stance, a physicalist, would claim that of course this makes sense.  The brain does not equal the mind, for we rarely find such a simple association is rarely found in nature.  Instead, it would make much more sense to narrow the statement to say every mental state we can possess is based on a brain state.  And sometimes the brain states are unrelated to conscious thought or processing. Maybe these states are the parts being affected by the small lesions in the studies mentioned above.

Of course, it is important to recall what we are referring to as “the mind.”  Descartes, from whom this original dualism stems, saw the mind as being a collection of ideas, memories, beliefs, and opinions that can be disconnected from the physical world.  So how can we try to change or alter this state?

Descartes: Author of the Meditations

Much of the psychopharmacology of the current era has been based on the belief that we can alter the mind.  Antidepressant drugs rely on changing the composition of cellular channels and levels of neurotransmitters to help patients rid themselves of emotional problems caused by “poor wiring.”  Another example shows that some pain medications block receptors in the body’s central nervous system to keep the signals from reaching the brain and forming full sensations.  And we even have ways of directly stimulating regions of the brains via implanted electrodes to activate the amygdala and invoke a fear response (Though this experiment has only been done on lab animals so the analysis of the effect on cognition is extremely limited.  Not to mention we have not taken into account the implications of animals’ mental states, as well as the fact that only outward behavior can be measured.).

Nevertheless, despite strong arguments for brain alterations leading to changes in behavior or mood, we still have no conclusive evidence that these alterations are affecting the root initiator of the mind.  With all our modern science and technology, we still have nothing resembling brain control.  We can only change influencing factors on the brain, such as physical perceptions like pain or moods such as depression.  These cannot lead to changes in belief or an alteration of how we recall memories.  Our ideas will remain our own, even if our brain chemistry is altered.

Perhaps the most apt metaphor is to compare the brain to another physical aspect of our being such as an arm.  Just as our brain controls the movement of our arm, our mind directs the brain to change in certain physical ways which will then allow it to function as the mind wishes.  The mind just works through the brain which works through the body to accomplish its ultimate goal- whatever that may be.

And just as environmental changes can affect functioning of a limb like an arm, external factors like psychopharmacological drugs can alter the functioning of the brain.  The key lies in that both are experiencing forces outside their existence which tweak how they respond.  And in the case such as damage to the neural cortices, the result is like breaking a bone in the arm.  You may still hold the same intentions but enacting them is challenged by an injury.

Through these examples I have strived to prove the imperfect connection between the brain and the mind.  The correlation between the two grows stronger as modern science progresses but the link will never be perfectly defined.  As correlation does not equal identity, we cannot say that the two are identical entities.  Thus a modified dualist view -which shows the brain is used by the mind like how the body is used by the brain- still holds sway.

Bird-Brained Bombs?

While Pavlov's dogs and B.F. Skinner's work with behavior conditioning are the quintessential studies of learning for psychology and neuroscience alike, the archives of experimentation have even stranger stories to tell.  Some are gruesome, but others are so absurd that you can't help but marvel at human ingenuity and creative thought.

My favorite example of "the odd" starts in the dire settings of America amidst World War II.  B.F Skinner, the famous behaviorist psychologist, wanted to assist in the war efforts.  In particular, he saw a need for improvement in the missile guidance of America's air craft.  The key issue was, we really didn't have one.  Bombers approximated when they were over their target and then dropped the full payload in the hopes that a few would accurately hit.  The sheer inefficiency of this system sent Skinner in search of a solution.  And what better experience did he have than working with operant conditioning?

His solution was to train pigeons to peck at a target through a glass lens marked with crosshairs.  As long as the target was in the center of the lens, the pigeon pecked at the center and the bomb flew straight.  But if the explosive began to veer off target, the trained pigeon would peck off center (in order to hit the target it saw through the glass), altering a complicated series of mechanisms which would change the angle of the bomb's fins and redirect it towards the target.

The military actually funded a good part of this research and initial tests looked promising.  However, by late 1944 the military withdrew their funding in favor of more immediately promising technology.  The idea was revived for a short time in 1948 and paid for by the Navy but ended permanently in 1953 after computer guidance was shown to be consistently reliable.

An image of B.F. Skinner's pigeon contraption.

Still, I can't help but crack up at the idea of pigeon-headed bombs falling on enemies.  Animal rights groups would be aflutter with animal cruelty and abuse claims nowadays.  Nevertheless, I'm perversely proud of Skinner and his finally thinking "outside the box."


*Get it?  B.F. Skinner is best known for the "Skinner boxes" he used to condition his animals in his initial testing.

Because I had a test today....

I don't really have a detailed topic in mind to dive into.  Instead, I thought it might be fun to bring in a part of my life which has been all-consuming for the past year and a half.  Because yes, while brains are my passion I also hold another activity as my personal addiction.  Here, this'll give you a hint.

I was very excited to score a head shot.

For those of you unaware of the differences in types of martial arts, this is an example of WTF (world taekwondo federation) olympic style sparring.  Since entering college, I've become enamored with the sport of taekwondo and the Texas Taekwondo team here at UT.  We train 6 days a week with the usual weight-lifting and sprints as well as the actual technique required for an effective fighter.

Now I see how this could be mistaken as off the mark from my usual subject.  But a large amount of current research is being done on exercise and its effect on your brain.  Sure everyone knows the old adage, "exercise your mind to stay healthy" but increasing evidence indicates you need a healthy body to house that mind as well.  For example, a study done with rats showed that the animals who got time on the wheel (and were more physically active) had a greater number of new cells in their hippocampus.  This showed both adult neurogenesis and survival of the new cells (provided, there were also other factors involved such as a reduced level of stress).

But simple, monotonous workouts aren't nearly as effective for complex organisms like humans.  Yes getting your heart rate up several times a week will increase your general health,  but the best bang for your buck in terms of exercise is taking up an activity which engages both your body and mind.

My personal sport of choice is taekwondo.  To most, it may seem a brutal brawl where someone is liable to be knocked out with no determining factors besides speed and strength.  But the way that we approach taekwondo at my school, the whole sport is understood as a physical chess match.  Of course you still have to be strong enough to make your kicks perform like you want but there's a much larger element of out-thinking the opponent.  You have to apply pressure, learn to read the signs to discover your opponent's favorite kicks, and then use those against them.

It seems to be simple but things get very complex very fast as you move up in belt rankings.  I started as a yellow belt but currently sit at red, nearly black, and I know I've had to think faster and more efficiently to reach this level.

Cheesy I know, but I think it gets my point across.

Interestingly, instead of my workouts physically and mentally draining me I find myself refreshed and sharper than before.  Taekwondo may eat up over 9 hours a week of my time but I don't feel my grades have lagged because of it.

If you're not already physically active, I highly recommend taking up an activity that challenges you both physically and entally. Don't try just going to the gym to run on the treadmill for a half hour.  It wont give you the same mental boost and you'll be left bored and probably wanting to end your workout regime.  Dancing, tennis, volleyball, basketball, and (of course) taekwondo, all offer an excellent way to stay engaged and fit.

But if you'd like to see more about the strategy behind taekwondo (as well as some sweet fights), check out our upcoming event.  We'll be hosting the Southwest Conference Fight-Offs February the 25th.  I guarantee a lot of excellent fighters and some exciting matches.

Saving the Brain

I want to revisit the topic of neurogenesis (the growth of new neuron cells) because while it may be that adult brains can form new neurons, they can't do so to the degree found with brains experiencing the critical period.  The critical period occurs when between late embryonic stages and early life.  This is when massive amounts of new neurons are created and preliminary synapses are growing towards as many targets as possible.

The power of a single synapse is weak, but together in a
circuit their power is incredible. 

After the critical period, there is a massive reduction in the number of connections between neurons.  The ones that remain are typically efficient enough to handle all the mental processes but the ability to "rewire" after this period is severely reduced.

However, some recent research is leading us to believe that there may be a way to reopen the critical period  and at least partially rewire our brains.  In fact, some antidepressants seem to be doing just that.  There's now evidence that anti-depressants like fluoxetine work by increasing BDNF (brain derived neurotrophic factor) which is hallmark of the critical period.  Fluoxetine requires chronic usage to get these effects but perhaps the antidepressant allows for the creation of new synapses and connections.  Maybe the rewiring is changing how information is processed in the emotional centers of the brain, thus relieving the depression of the patient.

A pill that changes how your brain is wired-
scary or amazing?

There's still plenty of research and trails we have yet to undergo before we understand all the mechanisms.  But this offers hope that neuroplasticity can be raised to the high level of malleability found during the critical period.

Roses are red, Violets are blue, Neurotransmitters make me love you!

In honor of today's Hallmark-funded holiday which is customarily filled with bright pink hearts and chalky candy handed out to all grade-schoolers, I decided to write about what makes us feel "in love."  Yes, you can read all the romance novels you want (*cough*Twilight*cough*) which expound on his chocolate eyes or her sensuous curves.  But when we move back to the basics, it's really just a soup of neurochemicals stirring around in your brain that cause that spark of love in your life.

Who actually eats these?

And truth be told, the biochemistry of attraction and love is still under research.  However we can safely say that there are 3 key neurotransmitters that make Valentine's Day special for all those people out there with their significant others.

The first and likely most recognizable is dopamine.  It plays many roles in the chemical signaling of the brain but is primarily associated with the reward pathway.  Whenever you get that rush of happiness from the first bite of chocolate cake, that's the dopamine kicking in.  In fact, addiction and the need to up the dosage of drugs over time like cocaine comes from the brain desensitizing due to the over use of dopamine.  And in the romantic sense, dopamine is the "drug" part of love.  It's the passionate, euphoric love that makes you believe there's nothing better than being with your partner.

How many roses do you think are sold each
 valentine's day?

And yet that's not quite enough.  Can you remember the first time you asked that girl to dance at the winter formal?  Or how about the anticipation before your first kiss?  Odds are your heart was pounding like a jack-hammer.  Norepinephrine is the neurotransmitter that provides this autonomic response.  It focuses your attention and physically primes you with those classic signs of nervousness.  Next time your hands turn clammy when you reach out towards your love interest, you can blame norepinephrine.

But these two neurochemicals play havoc on your brain if they're constantly swamping the circuits.  To keep an even keel yet stay connected to your significant other, we need oxytocin.  This compound is a long lasting messenger which doesn't give the same high as the others, but leads to a feeling contentment. Sometimes called the "cuddling neurotransmitter," oxytocin provides us with the companionship aspect of romantic relationships.  Without it we wouldn't have the same peace and stability in our long-term relationships.

Ok, so there are actually many more circuits and neurochemicals involved in love. It's an emotion not easily reduced to formulas and equations.  In my opinion, we could lecture on the biological components involved all day, but honestly I prefer to just listen to some Maroon 5 and eat chocolate covered strawberries!

If you want to hear more on this subject, I suggest checking out the original source:
http://www.radiolab.org/blogs/radiolab-blogland/2007/aug/28/this-is-your-brain-on-love/
Radiolab is a non-profit public radio program hosted by WNYC.  If you'd like to donate to their phenomenal program, please go to: https://pledge3.wnyc.org/epledge/desktop/radiolab/

Adult Neurogenesis- The Brain That Grows

When you first start to learn science in grade school, everything seems so set in stone.  The teachers say "this is how it is" and you just take them at their word.  But real science is nowhere near that stagnant.  In fact, the last 20 years have seen the discovery of one of the most intriguing aspects of neural development- adult neurogenesis.

Can you believe people used to think you could tell
personality traits of a person by examining their
skull shape? 

Up until the early 1990s, most scientists believed that after the initial growth of the brain and central nervous system, usually defined as the prenatal period, the adult brain produced absolutely no new neurons.

The reasoning for such a theory is relatively sound.  Based on the most obvious observations, the adult brain undergoes no major physical changes.  Once the basic structures are set, any larger structural alterations could possibly hamper the circuits which already exist.  Imagine a city with a simple grid-pattern of streets.  That would be the adult brain.  Most scientists saw the addition of neurons as adding roads on top of those existing and through an unordered method.  It would create a mess of traffic- both in the city example and in the neural system.

Here's an example of one of the cellular
stains used to test for neurogenesis.

The second reason neurogenesis was not believed to exist was because it's relatively difficult to spot cells dividing.  It took many attempts to devise a process to definitively show cell division in the allocortex.  To tag the cells, show them dividing, and prove that these were actual progenitor cells of neurons required several techniques including Brdu labeling, studies of canary's song, and radioactively tagged thymidine in DNA synthesis.

But all this work has undeniably demonstrated adult neurogenesis truly occurs in at least two regions of the brain.  The hippocampus' dentate gyrus isn't that surprising considering its role in memory consolidation.  The other core area of neurogenesis is the subventricular zone which is the tissue lining of the brain's ventricles- cavities in the center of the brain filled with cerebrospinal fluid.

However, there's still areas of research to be discovered.  I'm curious to see what papers in the future will have to say about our ability to grow new brain cells after that first spurt of development.

Different Kinds of Death

As living creatures, we tend to see death though a lens of complex feelings.  There's fear, revulsion, acceptance, and resistance all mixed in with several other shades of emotions.  But when you look at cell death, there can be a beautiful clarity found on the cellular scale.

Particularly, I mean to reference the difference in neuronal die-off between apoptosis and necrosis.

Let's start with the more intimidatingly named one.  Necrosis is pretty much exactly what it sounds like.  "Necro" has its latin roots in the death.  It's never a good thing to have unexpected cell death which is exactly what necrosis is.  It starts due to external damage to the cell which causes a disturbance in the cell membrane.  There are multiple ways this is accomplished but the end result is always a rupture in the cell walls and that cell "spilling its guts" into the extracellular matrix.  This changes the composition of the fluid surrounding the other cells in the tissue and can lead to a massive bystander effect.  Part of what makes brain hemorrhages so dangerous is this cascade of cell deaths and the damage they deal to their neighbors.

No mess death!

Apoptosis, on the other end, is a purposeful, regulated cellular destruction.  The name comes from the latin meaning "to fall away."  And in truth, that's really what these cells are doing.  Because believe it or not, our bodies produce too many cells in the early stages of development but then has to find a way to get rid of this extra baggage.  Apoptosis is the biological answer to the problem.  Cells receive an external signal which essentially sets a self-destruct sequence.  Because the process is controlled, there are no unwanted exterior effects.

So with these new vocabulary in my mind, I think I've decided I'l never die.  I'll just "apoptize."

Form and Function: Which one comes first?

As I continue my path along the story of neurogenesis, I've come across the historical argument between two relatively famous scientists over one of the most basic questions.  These two men, Roger Sperry and Donald Hebb, debated over the significant  question of how neurons actually know where to connect.

This is a nissl stain depicting the cellular
layering found in the V1 of the vision
processing part of your cortex.

In the developing brain, neurons face three major problems:
1. Which pathway to take?
2. Which regional target does the neuron need to reach?
3. What is the actual cellular target?

Each man had his own theory as to how neurons find the right path.  Hebb believed the model that experience forms the connections in the brain.  That because certain portions of the brain receive certain types of stimuli, they wire in a way that is most efficient to process that data and hence you get the specific "cytoarchitecture" (way cells are structured in a tissue) for different areas of the brain.

Sperry, on the other hand, saw the paradigm as form proceeding function due to chemical cues.  He believed that neurons knew where to migrate because of chemical signals which were excreted by the tissues which were to be the axonal destinations.  Imagine a mother holding an apple pie and wafting the scent towards her children who she wants to attract.  That's the basis of Sperry's view.

As it turns out, there are components of both in the actual biological system.  But what I find astounding is one of the famous experiments conducted by Sperry in the 1960s to support his hypothesis.  I like to call it "the kermit chemoaffinity test."

Apparently frogs were big as animal models
for science done in the 60s.

Essentially, he tested his chemical signaling theory by taking a live frog and rotating its eye 180 degrees.  Mind you this is with the optic nerve still attached and the eye was just rotated in its socket.  This literally turned the amphibian's world upside down, and the frog was unable to accurately catch flies because up was down and left was right to the poor kermit.

The next step was to sever the optical nerve and leave the eye rotated.  It's key to mention that amphibians are some of the few creatures who can actually reconnect some of their nerves.  If we were to believe Hebb's hypothesis in this particular instance, then the eye would rewire to turn things right side up- because use denotes how it will connect and that is how the frog would like to use the eye.  However, Sperry was proven correct. The eye rewired along the same lines as it started (due to chemical messages) and the frog stayed in an upside down world.

A New Hypothesis

Though this is more in an evolutionary vein than physiology, I thought it makes for an interesting topic for discussion.  Because while much of our current work on discovering what makes the brain "tick," animal models are the most common mode at getting about this information.  In other words, we often use animals such as rats and monkeys to serve as subjects and infer that the information we glean from them will apply relatively well for human systems.

Primates are often a great source of information in regards
to matching our physiological and social behaviors.

But not all species are alike.  Though these model systems often serve us well, some things can't be discovered through such a method- particularly higher order functioning.  But how are we different you might wonder.  Well the space assigned to various sorts of processing is one of the key elements.  Most other animals use the majority of their processing for dealing with sensory input like vision.  We differ in how we integrate the same type information as well as the additional work we do.  In fact there's a fascinating trend recently proposed by an anthropologist by the name of Dunbar.

He examined the density and amount of neocortical tissue found in apes and monkeys which led to an unusual correlation.  The best predictor for cortex size is the mean size of social groups that species interacts with.  So when species a of monkey lives within a social group of 20 individuals and species b interacts with 50, species b will have a larger degree of neocortex.

Dunbar used ration of brain tissue to body size to help
equate differences caused by simple body mass.

This correlation makes the basis for several interesting possible relations.  First, this might mean that there must be an evolutionary advantage to large social groups because species which work within such framework tend to have higher cognitive processes.

Second, it could be construed that being in a big group allows you to better use and hone your cognitive skills so you can process more with more developed cortex.

But last, and perhaps most interesting of all, the proposition that navigating large social groups is a highly complex process and requires a more developed cortex to handle.  This last one is of particular interest to me because it seems to tie psychology, sociology, and neuroscience into a single view.  The structure of our brain relates to our skill sets which assist in navigating the social world.  What a neat little bundle.

Of course there's still plenty of research to be done.   Just seeing a correlation does not immediately imply a causation.  And so far only primates have been examined.  How does this theory apply to animals like meercats or elephants who also live in large social groups?  What's your opinion?  Are we just seeing patterns that don't exist or is there really something to be said for this relation?

Neurogenesis

While I'm definitely not prepared to discuss the definition of life, I do want to start today's blogpost with one of the earliest stages we start at- the zygote.  Most high school students are comfortable with the notion of a zygote multiplying and becoming a hollow ball of cells called a blastula.  And the jump to diversifying cells follows that step with a vague conception that this leads to all the types of cells composing our bodies.

But how exactly do nerve cells, which are my primary interest, form?  What types of cells are they composed of?  This is where I hope to be of some assistance for understanding the neurogenesis of most known life.

So let's take it up from the blastula.  This hollow ball of cells undergoes a process called gastrulation during which the ball collapses in on itself and forms a double layer of cells.  This is the first step of cell differentiation between ectoderm, endoderm, and mesoderm.  Just for a general crash course, here's the end results of these primary tissue types:
ectoderm: epidermis and nervous system
endoderm: gut structures/internal organs
mesoderm: muscle, bone, and the circulatory system.

But what we want to focus on is the formation of the neural tube from the ectoderm.  The process is rather difficult to explain via text when a movie is much more descriptive.  But essentially a groove forms in the outside of the cell ball (called the neural plate) and the sides create neural crests which rise up and meet each other to create the neural tube.  Here's a video to help display the process.

The accuracy and consistency of this process is beyond impressive.  Have you ever considered yourself as a collection of cellular processes?  Just think how many functions and changes our bodies perform everyday simply to keep us alive!  It's amazing that through all our development and lives, we only suffer a limited number of medical problems.

Though google images had many more graphic pictures of
meningomycelocele, I thought it best to stick with some-
thing like this.

But they do happen every once a while, and the problems don't always have surgical solutions.  In the case of the formation of the neural tube, the most common human affliction is called spina bifida.  This occurs when there's incomplete closure of the spinal cord.  In particular, meningomycelocele is a form in which the spinal cord actually protrudes from the back.  The meninges fibers are exposed with none of the usual protective coverings, hence the name.  If the exposed tissue is low enough down the spinal cord, corrective surgery can be used to fix the problem.  But otherwise, the life expectancies for such a child aren't very good.'

If talk of this kind of physical abnormality makes you concerned, fear not.  Spina bifida is not a common occurrence and can easily be avoided by ingesting plenty of B9 folic acid.