In part 1 of our webinar series on understanding brain function, brain injury rehabilitation specialist Dr. Jeff Snell discusses the left brain, including motor function, language, sensory, emotions, and visual systems.

Speaker: Dr. Jeff Snell

Video Transcription


Thanks for joining us today. We’re going to talk about how the brain is organized, and particularly from the standpoint of the left brain and what’s it known for from the standpoint of differentiation of function. What aspects of our functional abilities really lie within the left hemisphere of the brain.

Functions that are predominantly located in one hemisphere of the brain versus the other are called lateralized functions and there are very definite aspects of functioning, some that are much more clear than others.

One caveat that I have to say about this is these findings represent general trends and there’s some degree of individual variation. So in some respects, we’ll be talking about some generalizations today.

The other is if you have ever gone in and done a popular psychology or Today magazine survey that determines whether you’re a left brain or a right brain person, unless you have physically surgically had the fibers that connect the left and the right side of your brain together, you are not a left brain or a right brain person.

The brain operates as a whole and there’s a big bundle of fibers called the corpus callosum that connects the left and right hemispheres and allow them to communicate with each other. When you say it in Latin, it sounds really fancy, but corpus callosum in Latin simply means tough body. That means when they did those original surgeries and looked at that particular structure in the brain, it was really hard to cut through. And so that’s where it got its name.

The only time that you see an individual typically that has had that bundle of fibers severed is someone who, because of a serious seizure disorder, required a surgical procedure that allows you to separate the hemispheres so that the electrical activity in one side doesn’t spread to the other side. So being able to prevent that from happening.

So generally speaking, although your brain operates as a whole, there are definite aspects of functioning that tend to be more left brain. And, those are the ones that we’ll be talking about today.

How Do We Know What the Different Parts of the Brain Are Responsible For?


How do we know what we know about what the left brain is responsible for and what it does? Well, one area is looking at throughout history, different observant individuals that have seen someone who has had some type of injury or has done a post mortem examination of a brain from someone who had a clearly defined deficit, and then making the connection that that ability must lie within the area that was different in this person’s brain.

Broca’s Area

Broca’s Area, noted there at the top of the slide, is one of those Broca was a French physician in the mid 1800s, who had a patient who was unable to speak. Voluntary language was lost to this individual, and he was only able to say the word “tan”. It’s something that today we would typically call aphasia.

So in other words, someone has damaged to a certain region of the brain, and it destroys their ability to produce fluent motor speech. Those individuals typically are aware of the fact that the words that are being produced don’t match what they are attempting to say, and it’s a very frustrating issue for those individuals. But in this particular case, Dr. Broca, had a patient who, when he attempted to speak only was able to say, “tan”, “tan”, “tan”.

He did a post mortem examination of this individual’s brain and found that he had a large lesion in the left hemisphere, basically, a little bit above and a little bit in front of what would be your left ear. So if you point to a spot couple of inches above and a couple inches in front of your left ear, you’re pointing in the general area of Broca’s area.

So if you have a stroke, or if you have some type of a penetrating injury that damages this part of your brain, one resultant functional deficit is often that of motor aphasia, difficulty being able to produce speech. So this was an instance in which you had an individual who had a naturally occurring damage to the brain and a physician who was able to look at and make the connection between that area and the anatomy versus the function of that area.

Phineas Gage

I think most folks have at some point heard the story of Phineas Gage. And so that is also another case in which a significant injury to the brain was followed from the standpoint of what physical functional changes resulted from that.

Phineas was a railroad worker who became famous for having survived having a metal rod projected through his head by an explosion. That rod penetrated his left frontal lobe, and from that he had some behavioral and cognitive changes.

Those changes were observed by and reported on by the physician who treated him, Dr. John Harlow in Vermont. And, Phineas’s story was actually very famous because it came at a time when people that studied the brain we’re trying to figure out does it operate as a single holistic organ? Are there localization of function? In other words, are there specific functions at points in the brain that result in certain behaviors are associated or tied to certain activities?

So the evidence in that particular case was one that the changes in his personality and behavior following his injury, were likely in the absence of any other explanation, directly associated with the part of the brain that was injured when the metal rod passed through his head. And so that became a very famous case in its time, and it’s one that oftentimes is one that gets people interested in the study of the brain to begin with. In early psychology classes that one often gets discussed from the standpoint of the brain’s anatomy and physiology and how that relates to function.

The Wada Test

The Wada Test is one that is more recent. That is named again after a physician who first performed it and became famous for performing it. And that is a test in which there is an anesthetic, a very brief acting anesthetic, that is introduced through the carotid artery to one hemisphere of the brain.

So there is a great deal of redundancy when it comes to the vasculature of the brain. And there is an independent vasculature that sends blood to the left side of the brain versus the right side of the brain. So in other words, if you have a stroke on one side of the brain, typically it only affects the tissue that’s deprived of oxygen, not that on the other side of the brain because the other side typically has normal blood flow.

In the Wada procedure, what you’re doing is basically anesthetizing or impairing, inhibiting one half of the brain by introducing a chemical only to one side of the brain.

Now the reason that this procedure is typically done is if you have someone who is potentially a candidate for surgery because of serious seizure disorders, you want to look at functions of language and memory in each hemisphere of the brain to see to what degree might you have to do a more advanced surgery to make sure that you’re not damaging anything that is critical from the standpoint of language or memory function.

So it’s an interesting test. It does come with some risks as well, but it’s a well established test when it comes to looking for seizures. And it also allows you to see when half of the brain is inhibited. The things that the person is not able to do under that condition certainly represents the fact that that part of the brain that is inhibited is responsible for those functions. So if you inhibit the left side of the brain, typically you get a disruption of language, both expression and reception, which is primarily a left hemisphere function.

Brain Imaging

And then the more recent aspects would be that of non-invasive brain imaging, being able to look at an intact, alive, awake and responding human being, what is their brain doing in a given situation. So things like diffusion tensor imaging, looking at pathways within the brain SPECT Scans or fMRI functional MRI scans, that look at what a neuronal activation in a general region of the brain is doing when you are performing certain tasks.

So, if you are looking at a picture of a penguin and naming it by saying that’s a penguin, then there are certain neuronal sequences in the brain that are going to be firing off looking at the different aspects of language and recognition and memory that are involved in that particular task.

If it’s a motor task, if you’re moving your right arm, there are motor neurons in the left hemisphere that are going to be firing and so these are ways of non invasively looking at that and seeing what is going on.

Left Brain Functionality


This is a kind of a global idea of the left hemisphere functions and this map by Stephen Holland is actually a very good kind of global summary of what different functions reside.

Now there are many more complex functions than what can be represented in a simple graphic like this, but this does kind of give us a broad idea of the different areas.

We’ll return to this graphic few times during the presentation and talk about specific functions. But if you’ll notice, as well, I just kind of wanted to put this one up early, there are a variety of different arrows on there that kind of represent functions that progress from a simple to a more complex process. So if you look, for example, at the very back of the brain, the occipital lobe involved in vision, there is a progression when it comes to being able to recognize the alphabet, from being able to determine an object from a field of background. So in other words, being able to pick out a stimulus being able to identify it.

The brain does that in terms of looking at lines and angles, looking at contrast. It then from that develops a sense of the shape of the letter, and then there’s a tie-in or an association with memory when it comes to recognition of that. What is that particular letter or letter groups? And, then as an adult, when you’ve trained your brain to read through many, many years of practice, you don’t actually read individual letters. We’re in the process of doing a research project right now that involves an eye tracking process when individuals are reading a paragraph of information. And it’s interesting to see how different individuals, those who have had brain injuries, those who have not had brain injuries, go through the process of reading a paragraph.

You are I, not having sustained a severe traumatic brain injury, oftentimes, in looking at a paragraph, are not going to be looking at every word individually. You tend to look at clumps of words or sentences, and your brain perceives that information as a whole.

If you are just a beginning reader, you’re much more likely to look at individual words, or even look at letters and letter groups within the word. So it’s a progression from a very simple, being able to pick something out, being able to identify it, being able to clump things together, and then assigning meaning to that.

And if you’ll also notice, the arrows largely kind of cycled back toward the parietal lobe. And that’s interesting from the standpoint that our brains seem to have a lot of discrete functions that all filter into the part of our brain, the parietal lobe, that is really responsible for this “so what” part of the information that we are viewing, thinking about or remembering.

So, the parietal lobe is where all those different parts and pieces typically get put together and ultimately give us a sense of our world.

Motor Function


Let’s start with our motor function, that’ll be the first area that we’re going to look at. So we’re gonna go through and look at several different aspects of functioning and relate them to the underlying neurology. But motor functioning, where we start out is one that is located pretty much in the anterior aspects of the frontal lobes.


So there is a pre-motor area, which is in the kind of middle aspect of the frontal lobes. And on the left side of the body, that information helps prepare and organize and sequence that particular motor firing sequence that is necessary to move some part of the right side of our body. So interestingly enough, the left hemisphere of the brain controls the right side of the body. So if you see someone who has weakness or lack of motor movement on the right side of their body, often times that is associated with damage to the left motor aspects of the brain. It’s one of the most common symptoms, for example, of someone having a stroke is they experience a loss of motor and sensory functioning on one side of the body. And, that stroke is occurring on the opposite side of the brain from the side of the body that is represented.

Those tracks, those pathways crossover in the brainstem around some structures called the pyramids and the pons, and then pass through another structure called the cerebellum, which interacts with the brain. So you’ve got a small brain, the cerebellum, at the very base of the brain, very base of your skull, which helps smooth out and regulate that motor movement.

The pre-motor area, which in the left hemisphere is involved in preparing the muscles to fire in the correct order, the pre-motor area involves not only what muscles need to move, but also doing so from the standpoint of cognition.

So, Don is sitting over here looking at me right now, and if I had a Nerf gun and wanted to shoot at him, I would have to go through a series of planning to move the muscles that are necessary to bring the Nerf gun up and pointed at him. Now, by that point, he’s going to figure out what’s going on. He’s probably going to get up and start moving. So I not only have to go through the process of figuring out how to fire the Nerf gun, I also have to figure out how to catch a target that is moving. How much do I lead? In what direction do I think he’s going to go? All those cognitive aspects of motor planning get sent to the pre-motor area to sequence the muscles that are necessary to make things happen the way that I intend consciously for that outcome to occur. That incorporates rules and logical reasoning and a lot of other aspects of concrete linear processes.

Now, I’m going to probably come back to this a couple of times, and if I forget to, let me go ahead and highlight it now.

The left side of the brain tends to be involved in things that follow a linear, predictable and concrete set of rules. The right side of the brain that we’re going to talk about next week is much better at fuzzy logic, is much better at approximation, is much better at generalization. The left hemisphere, it sticks to the rules.

I often use an example of the old Dragnet series, and the detective there who always said “just the facts”. “Just the facts.” When people started telling him things about what they felt or thought, he would say “just the facts”. Well, the Jack Webb character that was interested in just the facts would be a good analogy for the left side of the brain, which really needs, in order to achieve its goals, very predictable linear processes.

Motor Strip

So the pre-motor area sends that information to the motor strip of the left hemisphere. And, based upon the input from that pre-motor area, then it executes sending out signals to the muscles within the body. So our skeletal muscles that allow us to produce any voluntary motion originate on the right. The right side of the body muscles, that information originates on the left side of the brain. And as you can see there, there’s parts of the body that are laid out on that motor strip.

That motor strip is at the very back of the frontal lobe. So, the part of the brain that differentiates the frontal lobe and the parietal lobe is a fissure there, a crack in the brain, a wrinkle in the brain. And, that tissue just in front of that wrinkle is the primary motor cortex.

How much motor output do you need for a particular task? The brain in the pre-motor, area calculates that and then it sends that information. Now, the motor information, once sent, is also immediately monitored. And so if what you are doing is not achieving the goal or is over achieving the goal that you’re attempting, your brain will actually modulate that and regulate that.

I taught a class once where I had people pick up paint cans that were sitting on a table and their goal was to run up quickly and pick up five paint cans and bring them to eye level.

Well, the third or the fourth paint can would be empty, you couldn’t tell it by looking at it. What would happen is people would pick up the first one, they would get the second one a little bit quicker, the third a little bit quicker. And when they got to the empty one, well, you would raise it above eye level because it was much lighter than you expected. At that point, your brain had anticipated the amount of motor force, muscle force necessary to pick that pink and up to eye level as quickly as possible. But, because it didn’t have the same amount of weight, you put into much motor output.

Now, what you don’t do is throw the paint cans through the ceiling, which is what a robot that was programmed to put that much motor function into it would do. You recognize as you’re picking the paint can up, even before you get it to high level, that this one is lighter than the other ones, and you start decreasing the amount of motor output. So you tend to overshoot a little bit, but not so much as would be the case if it was purely a motor function that was programmed in.

Bottom line is, when it comes to motor function, it’s complicated. I end up saying that a lot when I start explaining things about the brain, mostly because any explanation is not going to cover every possible permutation of what can happen because there are so many different cognitive inputs that go into any of these outputs that we’re talking about.

Breathing is a good example of that. I mean, you’ve got regulation of your diaphragm that comes out of some midbrain structures and some brain stem structures, but you also have conscious control over it. So, you have a variety of different inputs that go into breathing. When I’m talking, I’m actually regulating purposefully my breathing so that it doesn’t interrupt in the middle of a sentence. If you’re singing, you have to figure out when you need to take a breath so that you can get through a particular passage, or if you playing a musical instrument.

On the other hand, if you decide that you’re just going to hold your breath and turn blue, at some point, your body is going to override that conscious decision, and you’re going to start breathing because it’s also an automatic function.

While I am presenting and talking today, I don’t really have to think about breathing because it’s an automatic function. I do that without really consciously thinking about it. But, it is something that you can take control of so that if you dive into a pool, you can regulate when you take your next breath so that you don’t suck in a good lung full of water.

So, motor functioning is one that is complicated and probably one of the more linear processes and easier to study from the standpoint of physiology and neurology. Emotions are harder to directly observe. Motion is really easy to see. And so, a lot of the early brain studies that are looking at what happens when a particular part of the brain is purposefully damaged, that’s typically done in animal studies because it’s really hard to get human volunteers to step up and have part of their brain cut out. And, quite frankly, I don’t think that would get past anybody’s IRB to begin with.


This is a representation, this human figure representation shows the amount of motor strip brain tissue that is connected or allocated to a given part of the body. So the body parts are represented proportional to the amount of motor strip that is dedicated to that part of the body, it’s called a homunculus.

Now, the interesting thing about this is, we have a lot more fine motor control in certain parts of our body. Those are represented much larger in that figure. So our hands, we have a lot of fine motor control over our fingers. We have a lot of fine motor control over our lips and tongue and larynx. So those aspects of physical functioning that require a lot more fine motor control, have a lot more brain dedicated to them.

An even more interesting aspect that we have learned over the last 50 years or so is that if you damage a part of the brain, the parts adjacent to it can actually take over that function. If you lose part of your physiology, your brain can actually remap that information to other digits.

So in other words, there was a study done where an individual that had a traumatic amputation of a couple of fingers. The parts of the brain that were previously sending information to those two fingers were remapped on to the thumb and ring finger on either side of the now missing digits. And so the brain does not like to have nothing to do and doesn’t like to have information. And so what happened when the person’s middle finger and index finger were dramatically amputated, their ring finger and their thumb had more brain tissue devoted to the fine motor control, which used to go to those digits that are now missing.

The remapping is an area that’s important to take into consideration when it comes to what we do from the standpoint of rehabilitation because it shows the brain’s ability to adapt over time to changes as they occur.



The next area that we’re going to look at is language functioning, and the explanation of “it’s complicated” probably applies better to this area than almost any other because language goes many steps further than just the linear processes.

Language is a means of communication. It’s a spoken or written system that a particular country or community utilizes to get information from person to person. And, for most individuals, language is predominantly a left hemisphere function.

I would say that the majority of you are right handed. So if I was having to place a bet on whether everybody listening right now was right handed or left handed individually, if I said right handed for everybody, I would be right about 90% of the time. So, you tend to make money if you can be right at anything 90% of the time.

If you’re right handed, there is between a 95% to 98% probability that all of your language functioning from the standpoint of the basic building blocks of language, the expression of language, and the receptive ability to understand language is in the left hemisphere of your brain.

Individuals who have a left hemisphere stroke often present with right motor impairment and with language impairment because the majority of individuals have the majority of their language in the left hemisphere of the brain.

Now it’s a little bit more interesting when it comes to left handed individuals because there is a greater problem ability that the language dominant hemisphere for those individuals is going to be on the right side. The majority are still on the left, however, there is about a 19% to 20% chance that a left handed person will have the majority of their language functioning on the right side of their brain. And there’s about a 19% to 20% chance that they will have it blended across both. So in other words, their language functions are both a left and a right hemisphere function from the standpoint of what is traditionally a very lateralized process.

Now, you might ask what happens for the other 3% to 5% of right handed individuals who are not left hemisphere dominant for language? Well, those individuals are something that we call atypical lateralization, a fancy way of saying that it is not normal lateralization. So, they have most of their language functioning on the right side.

I’ve seen a couple of examples of that for individuals who have had very clear strokes. So in other words, a very certain part of the brain has been affected and other parts aren’t. They had a right hemisphere stroke, but they presented with classic aphasia. That would be indicative of someone who has an atypical organization.

So, again, to some degree, what I’m telling you is a broad generalization, and there are exceptions to every rule. And, human beings develop their own brain throughout their lifetime.


So, that for most individuals, you’re looking at the organization starting out with production of speech sounds, which would be the phonetic aspects of language, and then grammar, which is the spatial relationship of the words. So, in other words, putting words in the correct order.

Punctuation, when it comes to language, is also an aspect that has to be kept in mind. When you are reading a sentence, you naturally put in a pause when it comes to commas. That is a punctuation that within our culture, and within our language means there is a small pause at this point.

It is sometimes important for meaning as well. If you have ever seen the T-shirt that has the statement, “Let’s eat, Grandma!” If you remove the punctuation, you’re saying, “Let’s eat Grandma!”

Those two sentences, which are the same words in each case have very, very different meanings depending on whether you put a comma or an exclamation point in place. So, that is an important aspect when it comes to language as well. It’s not just the letters that you see. It’s the other pieces as well. Stop shaking your head, Tim.

All right. language functions in the left hemisphere include, again, the basic building blocks of language, in other words, recognizing the letters, being able to understand what the letters sound like, interpreting those sounds and being able to put together clusters of letters to make a particular sound or word. And then the complex functions where you add all of these basic functions together. Again, grammar being the organizational aspect.

I’ve got a question. I’m gonna pause for a second.

“How can you tell which hemisphere is your dominant side, other than waiting for a stroke?”

That is a really good question. From the standpoint of language functioning, if you want to go in and find out without having to actually open up your head, that non intrusive way of doing an fMRI and looking at what cells are lighting up when you are doing a language-based task is probably the least risky way to do that.

From a truly functional standpoint, you have programmed your brain to operate your body, including aspects of communication. And, for you, if it’s working, it really doesn’t matter whether it’s left or right. The only thing that really is critical when it comes to that is if you do have an injury on one side of the brain or the other, whether or not that particular function is is compromised.

So again, for most individuals, if someone comes in and they have had a stroke, and then the medical records report that they were unable to provide history because of an inability to produce language, then you would be pretty sure in most cases that that was a left hemisphere stroke. So, an educated guess, is allowed in that particular case.


The vocabulary that you have within your brain is the lexicon of words that you have stored, basically your warehouse of words and what they mean. And, each of us have unique associations that we connect with words as well.

So, when you hear a particular word, you not only know the meaning of that word. When you say, “I saw a whale on TV last night”, the word “whale” is going to bring different associations for different people. If you’ve ever been on a whale watching expedition, it might make you think of what whales smell like. You may not have that association, if you’ve never been around an actual whale. If you like to watch Sponge Bob, you know that Crusty Crab’s daughter is a whale. So, that association may exist. Everybody has different connections within their brain when it comes to the words themselves and what other ideas those bring up.

Verbal Abstractions

In addition to the linear process of language, we also have the ability to have abstraction. Within a culture, you will typically have unique phrases that mean something other than what the words say. So, the classic, “don’t cry over spilled milk”. You know, oftentimes, you might ask a patient, if you’re doing an evaluation, what does this particular abstract phrase mean?

So, what does it mean when people say, “don’t cry over spilled milk”? If someone has damage to a certain part of their brain that impairs or compromises their ability to engage in that abstraction, they may process that language in a very linear and concrete fashion. So, I should not cry if I spill milk, is a literal interpretation of what that means, as opposed to, you know, don’t make something bigger than it is. Don’t overreact to a situation.

Linear Language Processing

Language processing is typically linear, particularly on the left side of the brain. We often joke about scientists being very left brain type people because they do things that follow a rigid set of rules. They have to adhere to that set of rules in a research setting in order to know whether or not their results actually match what their prediction and experimental process is designed to measure.

That linear processing lends itself from a language standpoint to a rather poor ability to understand the intent of language, rather than just the words themselves. The left side of the brain, when it comes to communication is probably best represented by email or text messaging because all you get is the words themselves. You don’t get typically a sense of context. Unless you know the person very well, you don’t typically get things like sarcasm or humor because, again, those rely on other aspects of context and situation that may not exist in just the words. So, you have to be cautious sometimes in attempting to use sarcasm in an email or in a message unless the person knows you very well because it may come across as very condescending or insulting, when in fact, that’s not what you meant.

Internal Dialogue

Internal dialogue we’re going to talk about a bit more later in this presentation when we talk about emotion. But, basically it is the ongoing language code that is constantly running in your head. When we talk about mindfulness, one thing that people often think of with mindfulness is mindlessness. I need to make just all of this noise in my head go away. I need to make my mind stop thinking.

Well, your mind is designed to think, and nothing that you can do is going to make it stop thinking. You cannot clear your head of all thoughts, because your mind is a thought engine. That internal dialogue, that constant chattering monkey that we all have in our head that never shuts up. Again, we’ll talk about this with emotion. But, sometimes that can be very negative experience as well, when our internal dialogue is producing for us negative perceptions that we attribute to other people.

Motor Speech

Our motor speech comes out of the left hemisphere of the brain and really is, from the standpoint of like we talked about with motor functioning, a function of being able to produce language.

As I said early on, Broca had a patient who couldn’t produce motor speech fluently. He found later that an area of the brain was damaged. To this day, we call that piece of the brain, Broca’s area. And, Broca’s area is attributed to the ability to produce fluent, expressive language, which is motor speech.

Receptive Language

A little bit further back on the temporal lobe, the posterior aspects of the temporal lobe, there’s actually an area called Wernicke‘s area. And, as you might expect, it’s because a fella named Wernicke figured this one out. That is the receptive language part of our brain, and damage to that part of our brain makes it very, very difficult, if not impossible, to understand what other people are saying to us. So, a stroke in that area of the brain or damage to that area of the brain can result in a lack of function that compromises our ability to understand what other people are saying.

Language function in the left hemisphere also includes what you consider to be those symbolic arrangements. And so if you look at a clock, if you look at the numbers of a clock, what does that mean in terms of time? That is a representative aspect of communication. It is a written language from the standpoint of being able to know what the face of the clock says.

However, you have to learn that it is representative of something. In this particular case, what time of day is it? You also have to learn spatial arrangements and functions. You have something called a relational frame of language within your head that allows you to look at things arranged on a desk, things arranged on a page, things arranged in the natural world, and your brain automatically categorizes things that are to the left, things that are to the right, things that are above, things that are below, things that are on, things that are under, things that are near, things that are far. These are all spatial concepts that assign a word to an aspect of something within our visual field or even within our auditory field. Being able to hear a sound with your eyes closed and know does that come from the left side or the right side. That’s a spatial abstract function that is largely a left hemisphere because it follows a set rule. It follows a very sequential organized process, and that tends to be a more concrete and a more linear process.

So again, if you look now, back to the temporal lobe and the occipital lobe, you’re looking at language aspects of being able to recognize the sound of language. If you look at that flowchart, from your ear, you recognize both the frequencies now, the phonemes associated with certain words. You’re putting those words together and recognizing that as a word sound. You’re putting words together to make sentences. And it’s a progressive process of increasing complexity that gets filtered up to the parietal lobe, which allows you to be consciously aware of the information that’s being provided and what that information means to you in the sense of the context that you’re in.

So, very simple things get added together to make very complex things, which then have even further meaning depending on the environment or the context of the situation in which you’re located.

From the standpoint of language functioning, again, our vision and reading our ability to get information in on the basis of letters and combination of letters that we call words, and that eventually becomes an automatic function.

All of that is something that occurs in the left hemisphere of our brain, and so damage to that part of our brain can result in a loss of any of those functions. So damage to the more anterior or frontal aspects of your left hemisphere tend to result in expressive language deficits or difficulties organizing or putting together words correctly.

Damage to the more posterior or rear aspects of your left hemisphere tend to be more compromising from the standpoint of visual input of words and letters or even understanding from auditory standpoint, the information that is coming in.


Now, I found a brief little video that always seemed to me to be very fascinating that I’m going to run now. It’s about three minutes long or so. And this originally came off of NPR, and it is a discussion about an individual who is a writer who had a stroke that affected his ability to read.

The writer who couldn’t read. Have you ever thought, even for a moment, that the part of your brain that controls writing could be different than the part that controls reading? Consider the case of Mr. Howard Engel, the celebrated author of numerous detective novels. The year was 2001. The place was Toronto, Canada.

“When I woke up in the morning, I wasn’t aware that it was any different from any other morning. All the normal things looked in their normal fashion. I went out and picked up the morning paper and found that it seemed to be written in Serbo Croatian or something strange and surprising.”

He continued to look through the paper and while the layout and pictures all look familiar, all of the words were wildly distorted.

“The conclusion that hit me next was I’ve had a stroke.”

Mr. Engel recovered quickly in the hospital, although he was left with alexia, also called word blindness. His eyesight was normal, save for the fact that he was unable to differentiate the shapes that make up letters and words.

“I think it would now look like gibberish with an English origin. It was quixotic in that a P would become a B or an S become an R.”

Amazingly, however, he found that when taking a pencil in hand, he was still able to draw the shapes of those letters. He was still able to write.

“Yes, and I found that I could write with rather refreshing ease. And then of course, what I had written after an interval would become the same sort of gibberish found in the newspaper.”

All of this sounds utterly illogical and baffling until you start to look at it this way. Your eyes only see the shapes that make up text, but it’s your brain that identifies the shapes as words and letters and assigns the meaning. If the brain can’t process signals from the eye, but it can process signals from the hand just fine, there’s no reason why you can’t still draw the shapes that you know to be letters and words.

With that in mind, Mr. Engel began using motion when he took the painful steps towards starting to read again, every time he reads now he will identify words by tracing each individual letter on the page with his finger, or in the air.

“I’ve also tried writing on the roof of my mouth with my tongue, or now I’ve moved it to my lower teeth. I just sort of traced the word in my mind with actually moving my tongue to form the letters.”

Amazingly, Mr. Engel has been able to pin two books since the stroke,

“I was surprised that the ability to read and the ability to write, while similar, are not identical.”

Any final thoughts, Mr. Engel?

“One of the first things they told me with alexia, that my spelling would go to hell, and it certainly did, but it didn’t have far to go.”


Very interesting. All right now. So, from the standpoint of the separation of language and aspects of those physical versus things that would be more visual, that’s just an interesting discussion there from an individual. And, interesting as well, from the standpoint of recovery of that function. From exactly how Mr. Engel was able to utilize a separate physical way he converted vision into a physical motion, which allowed him to regain that ability. So just a striking type of discussion there.

Sensory Function


Next, we’re going to talk about sensory functioning. The left hemisphere, similar to the motor strip, also has a sensory strip. So, represented in green by the little brain up in the top right corner, that sensory strip is a map similar to the motor strip of the different parts of our body that is laid out again, according to the amount of brain tissue that is devoted to that particular area of sensory input.

So, that is information that is coming in that allows us to know if something is rough or smooth, is it hot or cold, we have pain receptors within the body. So when you get up in the middle of the night, and you bang your little toe into the coffee table leg, if it is your right toe, that information is going to the sensory strip on the left side of your brain, which is lighting up like a Christmas tree and telling you how much that hurts. So that information gets passed across.

The brain has the capability of running that pain signal, even in the absence of input, which is what we have talked about previously from the standpoint of chronic pain. Even if you are missing a particular limb, you can still have pain in that limb something we call phantom limb syndrome. I’ve had a traumatic amputation of my left arm, but I still have the right part of my brain that processes what used to come in from my left arm, and so I can have pain in an limb that doesn’t even exist anymore.

So it is retraining. The brain has the capability of changing that after an injury or when that network has been impacted by the experiences that we have. So you’ve got all of these perceptive including things like something we call proprioception. If you close your eyes and you move your limbs around, you can tell where your hand is on the basis of motor information coming in from your joints and muscles.

On the side of the road, if you have ever had to go through one of these tests where they are looking to see if you’ve had too much to drink, they will have you tilt your head back and close your eyes and touch the tip of your nose with your index finger. And the way you do that is through proprioception. If you try it right now, when you are hopefully not terribly intoxicated, it should be relatively easy to get your finger to the tip of your nose because your brain knows where your finger is, even if you can’t see it. So that information is constantly coming in to our brain and being processed 24/7. And so it receives that information and allows us to be able to help regulate as well our motor as well as preserve our bodies by not ignoring injuries. It makes us pay attention.


From the standpoint of emotional functioning, the left hemisphere of the brain has traditionally been believed to be very different than the right side of the brain. And there’s certainly evidence for that within individuals who have had injuries that globally affect one hemisphere, in the absence of any effect to the other. So in other words, I’m typically talking about strokes here are seizure disorders that are limited to a single hemisphere of the brain.

So, if you look at in the same way Broca did, if a person has a unique type of presentation, and then you look at the part of the brain that has been impacted by an injury or a disease process, that allows you to make some inferences, that that part of the brain must be responsible for that particular function.

The way that this information is known as traditionally individuals that have had strokes, typically a middle cerebral artery stroke that affects the greater portion of one hemisphere of the brain. If that hemisphere stroke occurs on the right side, you tend to get an individual who has a relative lack of emotional response. In other words, they may have a very limited range of affect. And again, think of the scientist in the lab, who is just the facts, just the rules, very concrete and very linear, not a great deal of woo hoo and emotion.

When the latest scientific discovery comes down, the right side of the brain tends to be much more emotional, much more reactive. And if you have a stroke, that basically impairs or shuts down the left hemisphere aspects of your brain, then you tend to be more dominated or ruled by the right side from the standpoint of emotions.

So individuals who have had a stroke that shuts down the left side of the brain, the right side becomes more dominant. And so you tend at that point to have someone who tends to be more emotional or has more difficulty regulating emotions.

The right hemisphere is also more indicated in the perception of emotions in others than the left hemisphere is. So the left hemisphere itself doesn’t appear to be very good at recognizing what other people are feeling, as opposed to the right hemisphere, which is that seems to be a much more dominant ability.

The emotions as well. From the standpoint of the left hemisphere, as I said, tend to be much more dominated with a more regulated, a more linear process and less reactive.

There have been some laboratory tests that have shown that, for example, in mice, when the left cerebral hemisphere was temporarily deactivated by the use of chemicals, similar to the Wada procedure, even the production of T lymphocytes are reduced. That’s important from the standpoint of our immune system.

So deactivation of the right hemisphere didn’t have the same effect and the mice remained healthy. So damage to the left hemisphere of the brain, not only means that you tend to be more ruled by emotion, which is more of a right hemisphere function, you also tend to lose a little bit of your immune system functioning. You’re more susceptible to illness as shown within animal studies.

This physiological predisposition toward illness may also be related to our left hemisphere function and emotional regulation. If you think of the left side as being a more even keeled logical side of the brain, then there’s less emotional swings and it doesn’t tend to go as far in the extremes. Things are a little bit more clear cut from a motor standpoint, but from an emotional standpoint, we see those differences as well.

Our emotions are also tied to that internal dialogue. You remember I talked earlier about that internal dialogue being the language code that we run in our brain that is constantly evaluating things and judging things and determining whether things are over under beside left right behind in front of bigger or smaller, any aspect that you can assign to given object, including colo, or whether that person is friendly or not, those are all internal dialogue aspects that go along with that relational frame of being able to put things in some sense of order.

So when you are thinking about a previous conversation that you had with somebody, that’s internal dialogue. When you are making comments to yourself that you don’t necessarily say to someone else, that is your frontal lobe consciously shutting down the expression that would otherwise come out. Some individuals don’t have very good frontal lobe function, and they’ve never had a thought that they haven’t expressed, but that tends to be a little socially inappropriate because most of the time, when somebody says, “Do these pants make me look fat?”, they’re not really asking for you to give them an affirmative answer, even if that’s the correct response. So, being able to regulate that yourself, also under your control is important.

Now, an interesting thing is with your internal dialogue, you can actually change the accent as well. So if you want to think in a French accent, you have the capability of doing that without actually making any noise whatsoever. Most people don’t do that very often, but you do have the capability of doing it. So if you want to make a snarky comment in French about something somebody just said, but not say it out loud, you can do that. Your brain has that capability.

And again, it’s all of these discrete pieces that are funneling information in and allowing the “so what” part of your brain, the parietal lobe to make sense out of what’s going on.

Visual Systems

Lastly, a brief discussion of a very complex function that we all completely take for granted, and that is our visual systems.

The occipital lobe at the very back of the brain is the part of our brain that interprets information coming in from our eyes, the retinas send information from our right visual field to our left hemisphere. So you see there, you’ve got little blue lines that are feeding back to the visual cortex. Those blue lines are coming out of the retinas are receiving information from the right visual field, and then part of that crosses over from the right eye to the left, and then the left eye. It stays on the same side.

The visual area of the thalamus that all that information passes through allows coordination so that when we’re looking at something, both of our eyes can point at the same place at the same time. That also integrates with our understanding of a three dimensional world. If you hear a loud sound off to your left, your eyes get pulled to where that sound came from because all of that information is coordinated.

There is a question. Here’s the question. “Is there a particular area of the brain that cognitive behavioral therapy focuses on or works on, especially in regard to chronic pain?”

From the standpoint of chronic pain, part of it is getting an individual to be physically active at a level that would be commensurate with their baseline and at least doing that in a graduated and stepped process so that their brain can re acclimate the number of receptors and the amount of information and not overreact to the information that’s coming in.

I’ve got a whole chronic pain presentation that we could go into that it’s going to cover a lot more time. But basically, if you protect an area of the body, you’re not sending the same amount of sensory information to the brain, and the brain will begin to run its own program if you’re not giving it information.

And so, restoring the normal amount of information going back in is one of the processes involved with that. And then chronic pain also responds well to Acceptance and Commitment Therapy, which is a particular branch of cognitive therapy. Then I would encourage you to look into that as well.

There’s a lot of information available out there on the web when it comes to that particular mode of treatment for chronic pain. So back to vision, when it comes to information, our brain processes what our eyes are seeing. A couple of neurologists that also have a computer science background have basically said that our eyes are transmitting via the optic nerve, around 80 gigabytes of information per second to our visual cortex. In terms of computer processing, that is a tremendous amount of information that is being sent constantly, and we don’t have to be consciously controlling that process. Our brain simply presents that to us and makes us “so what” of it.

So again, back to the occipital lobe and that progression of complexity, your brain starts out with simple field and background and then eventually makes its way up to making sense out of what occurred. So there are several different levels of processing involved with any type of visual stimulus. You’re looking at edges, you’re looking at contrast, you’re looking at colors and then making sense out of what it is that you’re seeing. You relate that to other aspects within your left hemisphere, which allows you to name those objects or to decode what is written.

When it comes to memory, you have more verbal language on the left side of your brain. Our vision memory tends to be much more efficient than our verbal memory, so you can recognize a lot more faces than you can name people because those are two different types of memory, visual memory versus verbal memory. And so those two different aspects come from two different areas and have two different levels of necessary practice and repetition that are needed.

Question here, “Can injury to the cervical spine, specifically the C1 C2, affect vision and accommodation?”

The answer to that is yes. Through inflammatory processes, you can see some brain stem and even some cortical changes as a result of a very high spinal cord injury. The nerves, the cranial nerves, that control the eyes, and as I said earlier, the thalamic projections from our eyes that allow us to coordinate our vision are all kind of midbrain, just above the brainstem type structures. And if you have inflammation as a result of a high spinal cord injury, you can have a dysfunction within those tissues and within those structures and neuronal pathways within the brain that are necessary for the functional ability that you asked about. So the short answer to your question is, yes, the longer answer is, and it’s complicated.

All right, I’m going to bring that one to a halt so that we got a couple more minutes and I will turn it back over to Tim I do thank you all for sticking with us through this presentation.

Categories: Brain Function