brain

Split-Brain Patients

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The corpus callosum is the bundle of never fibers that connect the two hemispheres of the brain. It’s the largest single structure in the brain, with some two hundred million fibers. As a last resort for epilepsy, this bundle can be cut in a procedure known as a callostomy. When this happens, a split-brain patient can occur.

What is interesting is that these split-brain patients do not appear outwardly abnormal. There is not any indication that they have a severed corpus callosum if you saw them walking down the aisle at your local supermarket. They do not make weird facial expressions or odd gestures, they do not walk or speak ‘funny.’ They seem just like you or me.

But the evidence for their disorder abounds in the lab.

When the corpus callosum is severed, the two hemispheres of the brain, the left hemisphere (LH) and the right hemisphere (RH), cannot communicate well (this is why cutting the corpus callosum works in epileptic patients: the electrical discharges remain confined to one hemisphere instead of spreading between the two). Language is usually localized in the LH, while abstract thinking is the domain of the RH. (The whole thing about left brain is logic and right brain is creativity is true, but not really. The hemispheres are important for certain tasks, but overall, the whole left-brain-right-brain thing is overgeneralized and exaggerated. Our brains are far more complex than that).

One experiment involved a patient named VP. VP sat in front of a screen that played movies to the RH. The movie was a violent one, with people getting pushed off balconies and firebombed. But after watching the movie, VP could only remember this much: “a white flash, perhaps a few trees but definitely no people.” But when asked about feelings or emotions, VP said this: “I don’t really know why, but I’m kind of scared. I feel jumpy. I think maybe I don’t like this room, or maybe it’s you, you’re getting me nervous.”
The RH experienced the emotions (nervousness, fear) and processed them, but with the severed corpus callosum hindering interhemispheric communication, the left hemisphere was unable to figure out the source of the emotion.

Another experimenter flashed laugh to the RH of a split-brain patient. The patient laughed. Remember, language is a LH task. When the experimenter asked the patient what they were laughing at, the patient responded, “Oh, you guys are really something.” The LH gave a verbal explanation for the laughing. In this case, the LH was trying to interpret the laughing and trying to understand its cause, even though it actually did not. The LH, as the experimenter explained, is aware of what the person is doing and tries to interpret from there, rather than understanding the actual cause for the behavior.

Split-brain patient ‘Joe’ was tested in an experiment about visual fields. In the experiment, Joe sits in front of a computer. The computer screen has a dot in the center of it where Joe is told to stare at. When Joe focused on this central dot, everything on the right side of the screen is processed in his LH (remember, the right side of the brain controls the left side of the body, and vice versa). Since the LH is dominant for language, Joe should be able to read or say what he sees. The rest of the screen is a blank white screen. In intervals, words and images are flashed on the right side of the screen (i.e. to the right of the central dot). When Joe sees a word or an image, he reads or says it aloud to the experimenter.

For example, one of the words was tree. Joe would read car aloud. One of the images was a bundle of purple grapes. Joe told the experimenter grapes.
What’s interesting is when a word, for example, pan, is flashed to the left of the dot, Joe isn’t able to say what it is. He just says that he didn’t see anything. What gets even more interesting, though, is when he is told to draw what he says he didn’t see. He does so, drawing with his left hand, which is controlled by his RH. The result is a drawing of a pan. Then when Joe is asked what it is that he drew, he says pan.
What happened is that when the words or images were flashed to the left side of the dot, the information would go to his RH, which is not involved in language. Therefore, Joe was not able to say what an object was, because his RH from disconnected from the language-oriented LH.

Don’t worry, it gets stranger.

At one point, a picture of a saw was presented on the left side of the screen, and a hammer was shown on the right side if the computer screen. Joe says he saw a hammer.
He never says anything about the saw. But when the experimenter tells Joe to close his eyes and draw with his left hand, guess what he draws? The saw. And guess what he saws when he is asked what it is that he drew? That’s right, a saw.

Experimenter: “What did you see?”
Joe: “Hammer.”
Experimenter: “What did you draw?”
Joe: “Saw.”
Experimenter. “What did you do that for?”
Joe: “I don’t know.”

The effects are not just seen with patients staring at computer screens. Take a blindfolded non-split-brain individual and put a ball in their left hand. Their RH knows what the ball is, and this information goes to the LH, which is able to verbalize and say that a ball in is the person’s hand. But do the same thing with a split-brain patient, and they will not be able to say what the object in their hand is. They know what it is, what to do with it, can draw it, but they cannot give you its name.
Lingual description is out of their reach.

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Somatophrenia

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Look at the right side of your body. It’s yours, right? Or maybe it’s your neighbor’s…

 

Somatoparaphrenia is caused by damage to the right parietal lobe. The similarity of this disorder to BIID, coupled with the childhood onset of these disorders, suggest both may be congenital disorders, that is, present from birth. The disorder is a delusional belief concerning the contralateral lesional side of the body, meaning that the side of the body opposite the side of brain damage is affected.

 

This disorder should not be confused with asomatognosia, which is unawareness, rather than delusional disbelief, of a limb, usually the left arm.

 

Patients with somatoparaphrenia deny ownership of either a limb on one side of their body, or an entire side of their body. A sufferer might be adamant that their right arm and leg are not theirs, not part of their body.in many cases, the denial of ownership is of a paralyzed limb. Often, it is the left arm that is denied, as this disorder comes up often in right-brain-damaged patients. The denied limb may even be treated as an individual, given a name, treated as a child and taken care of. This shows how much the patients really dissociate themselves from ownership of the limb.

 

What do you think some of these sufferers ask for in terms of treatment? You guessed it: amputation. Again, the ethical issues that come up in BIID amputations apply to somatoparaphrenia as well.

 

One individual, suffering not only from somatoparaphrenia, but also schizophrenia, believed his right arm and foot did not belong to him. He said that his arm belonged to a woman he knew named Maria, and that his foot could not belong to him because it was a “big foot only suited for work.” This case is considered one of the few in which schizophrenia and somatoparaphrenia are documented in the same individual.

 

You may think, “Well, why don’t you try to ‘prove’ to the patient that their limb is theirs? Why, you can pinch their denied arm, or kick their denied foot. Or you can hold up a mirror to them and ask them to move their denied limb. And once they realize they can move that limb, voila! Problem solved.”

 

If you thought something along those lines, you were thinking like a researcher. Problem is, even if these things are done to the patient, they still deny ownership of the affected limb.

 

 However, there has been some success with a mirror experiment. This experiment was the first to describe that viewing a limb through a mirror alters limb disownership of a previously denied limb. What was done was a simple technique:

Take two groups of somatoparaphrenia patients. One group viewed their denied hand as it lay on a table. The second group also laid their denied hand on a table, but in front of them was a mirror which reflected their hand. The patient then viewed their affected limb in the mirror. There was no way for the mirror-group patient to look at their hand because a cardboard cutoff was placed around their neck to prevent them from being able to see below their neck. The results are startling: the first group, with no mirror, continued to deny their limb. But the mirror group accepted their limb as their own, so long as they viewed it through the mirror. If they stopped viewing their limb in the mirror and looked down at their hand on the table, they reverted back to denying their hand.

 

This mirror experiment is very interesting and is reminiscent in some ways of the rubber hand technique. This technique goes something like this:

 

Stick someone in a chair in front of a table. On the table is his left hand, hidden from his view by a screen. On the table is a lifelike rubber left hand and arm. The subject focuses their eyes and attention on the rubber hand and arm. A scientist stroke both the person’s hand and the rubber hand simultaneously, in the same area of the hand. Guess what happens?

 

The person feels a sense of ownership of the rubber hand. As one subject put it: “I found myself looking at the dummy hand thinking it was actually my own.”

 

The rubber hand illusion suggests that our self-awareness of our body can be manipulated and even altered through the senses. In effect, the brain uses the sensory modalities to construct and distinguish self from non-self. What do you think this mean in terms of somatoparaphrenia?

Ion Channels and Ion Pumps

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Signaling in the brain depends on the rapid response of neurons to changes in stimuli. These rapid responses are due to the presence of ion channels in the nerve cell membrane. Each ion channel is primed to respond to specific stimuli, either chemical or physical. They also have the property of heterogeneity: there are different types of channels in different parts of the nervous system, each one specific in what kind of ion they transport across the nerve cell membrane.

 

In addition to these ion channels, nerve cells also sport ion pumps/transporters. These pumps do NOT contribute to rapid signaling, but are more important for establishing and maintaining ion concentration gradients. Ion channels, on the other hand, are limited to the passive transport of ions down their concentration and electrical gradients.

Therefore, two main differences between ion channels and ion pumps are that ion pumps regulate active transport of ions, which makes sense considering they transport ion against their concentration gradients. This active transport utilizes ATP (incidentally, the brain uses about 20% of the body’s total energy; much of this 20% is due to the maintenance of the ion concentration gradients via ion pumps).

Another difference between ion pumps and ion channels is that the ion channels have a water-filled pathway through which ions flow from one side of the membrane to the other. Ion pumps, on the other hand, transport ions by undergoing conformational changes.

 

 

Myelin

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We know that neurons are encapsulated by myelin. But what makes the myelin?

 

The brain contains two major classes of cells: neurons and glia. Glia are responsible for creating the myelin sheath, as well as having many other functions.

There are different kinds of glia, including Schwann cells, oligodendrocytes, astroctytes, microglia, and more. The Schwann cells and the oligodendrocytes are responsible for the myelin sheath. Schwann cells do so in the peripheral nervous system (PNS;part of nervous system that isn’t the brain or spinal cord, so, effectually, the nerves), while the oligodendrocytes are responsible for myelin in the central nervous system (CNS;brain and spinal cord).

 

Both Schwann cells and oligodendrocytes produce thin sheets of myelin that wrap many times around an axon. The myelin in the PNS vs the CNS are similar, but still have differences.

 

 

How the Neural Tube Develops

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The formation of the nervous system during embryonic development is a fascinating topic. The embryo begins as a flat disk with three layers, one of which is the ectoderm from which the skin and nervous system arise.

A part of the ectoderm gives rise to the neural plate. In the neural plate, a groove, called the neural groove forms, whose walls are called the neural folds. These folds fuse and form the neural tube. This is called neurulation.

The entire central nervous system develops from this neural tube.

Neural tube formation is a crucial piece in the development of the nervous system and it occurs only three weeks after conception. Failure of the neural tube to close correctly is a common birth defect, but can be prevented through proper maternal nutrition. The birth defect is linked to something that many women know about: folic acid.

Dietary folic acid supplementation can reduce the incidence of neural tube defects by 90%.

Failure of the anterior, or front, part of the neural tube to close results in anencephaly, which is characterized by a degeneration of the skull and forebrain and is always fatal.

Failure of the posterior, or end, part of the neural tube to close results in spina bifida. Though not fatal, spina bifida requires surgery and expensive medical care.

Good dietary sources of folic acid are spinach, liver, beans, eggs, and oranges.

The neural tube goes through a process of differentiation, or development of specialized parts. The first step in braindifferentiation is at the rostral end of the neural tube: three swellins called the primary vesicles.

The entire brain is derived from these three primary vesicles of the neural tube.

One of the vesicles is called the prosencephalon, also called the forebrain. Behind it is the mesencephalon, or the midbrain. The third vesicle is the rhombencephalon, or the hindbrain. The rhombencephalon connects with the neural tube at the caudal end to form the spinal cord.

It is easy to see how preventing problems with the neural tube is crucial for proper brain and nervous system development in a fetus.

 

My original article can be found here. 

Intro Neuroscience

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Inside our craniums is an organ so spectacular, so inconceivably fascinating. This organ weighs approximately three pounds and allows us to perceive our world and understand it. Your brain allows you to predict the future and consequences of actions, engage in empathy towards fellow human beings and even animals not of your own species, and allows you to think lofty thoughts and experience a gamut of emotions.

If not for your brain, you would cease to be human.

The human brain is composed of billions of neurons. It was once thought that the number of neurons one is born with is the limiting factor to the number of neurons one will ever have. Neuroscience has disproved this theory. Your brain engages in neurogenesis, which is the birth of new neurons. But here’s the catch: these immature neurons have to connect with other neurons in a short time frame, or else they die.

Use it or lose it.

Neurons makes up only about 10 percent of your brain mass, though. Ninety-percent of your brain is glial cells, which support neurons by protecting and nourishing them. There is a shift in neuroscience research that is beginning to focus on these mysterious glial cells to the point some researches have begun to call these cells “the other brain.”

There is a book by R. Douglas Fields (Simon & Schuster, 2009) entitled, “The Other Brain,” that describes the role damaged or otherwise dysfunctional glial cells play in the development of mental diseases, including Schizophrenia.

There is much excitement on what unraveling the secrets of glial cells will hold for the future of neuroscience and the development of cures and treatments for various brain disorders.

It is your brain that makes you unlike any other organism. No other animals can plan and coordinate events like a human can. It is our cortex, or the top layer of the brain, the most evolutionarily advanced region of the human brain, that allows you to make decisions, plan, utilize logic and rationalize through things, and even control emotions, such as anger or fear. Without the cortex, humans would have no cognitive advantage over other animals.

However, humans are not the only animals to be able to plan or think ahead. Gorillas have been found to use long sticks as a way of testing the depths of a river before attempting to cross it. Chimpanzees have been seen to use sticks to fish out ants from logs.

However, the human cortex is more developed than other animals, including other primates. It is this advanced development that allows humans to engage in higher level thinking that merely utilizing tools.

Without the advanced development of the cortex, humans would not be the complex creatures we are today. Evolution is progressing and the human brain will continue to progress as well. Only time will tell where the evolution of the human brain will lead our species.

 

I wrote this originally here.