Author: Jared Tanner

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The Corticospinal Tract

The corticospinal tract is a descending motor pathway originating in the Primary Motor Cortex (Brodmann’s area 4) and terminating at various levels in the ventral horn of the spinal cord. The corticospinal tract descends through the posterior limb of the internal capsule then down through the cerebral peduncles into the brainstem. In the brainstem the corticospinal tract remains in the ventral portion, passing through the pyramids on its way down. In the caudal brainstem (just above where the spinal cord starts) 90% of the the corticospinal tract decussates (crosses) to the contralateral (opposite) side and continues down through the dorsolateral spinal cord. This portion controls limb movements. The remaining 10% remains in the ventral spinal cord and is largely responsible for bilateral axial (trunk) movement. From the dorsolateral spinal cord, the axon (that started in the cortex) enters the ventral horn of the spinal cord at the appropriate level (e.g., cervical for arms or lumbar for legs) then exits through the ventral root to terminate on the appropriate muscles.

Through this tract, the cortex controls much of the movement of the body; as such, it’s vitally important for our functioning. Damage to the tract results in an upper motor neuron disorder, with paresis (weakness instead of complete paralysis) and the Babinski reflex fairly common symptoms. Soon after damage, a patient might have flaccid paralysis though with little to no movement of the affected limb(s). As the body starts to recover slightly, spastic paralysis usually sets in with jerky, often uncontrolled limb movements. The corticospinal tract is one of the largest pathways in the central nervous system; it’s one of the most important for motor functioning as well.

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The Philosophy of Science

I wrote this response to someone who questioned the assertion I made (on a different website) that science is not impartial. Let me know what you think.

I don’t really have room or time to get into a philosophical discussion; this is a discussion that takes months to talk about. As a note, I’m not just making things up, I’ve studied epistemology in college. One of the philosophical foundations of science (science is all based on philosophy, which is one reason in the U.S. all science doctorates are PhDs – Doctor of Philosophy) is empiricism. I’ll quote from Wikipedia because in this case it is accurate.

“Empiricism is one of several competing views about how we know things, part of the branch of philosophy called epistemology, or “theory of knowledge”. Empiricism emphasizes the role of experience and evidence, especially sensory perception, in the formation of ideas, while discounting the notion of innate ideas.”

“In the philosophy of science, empiricism emphasizes those aspects of scientific knowledge that are closely related to evidence, especially as discovered in experiments. It is a fundamental part of the scientific method that all hypotheses and theories must be tested against observations of the natural world, rather than resting solely on a priori reasoning, intuition, or revelation. Hence, science is considered to be methodologically empirical in nature.”

There are other competing philosophies to empiricism. Rationalism is one of those; although in our day some ideas of rationalism are combined with empiricism. Materialism (all entities are matter and reducible to smaller entities, e.g., atoms) is another foundation for most science.

Because modern science is based on specific philosophies with specific assumptions (e.g., that all is matter) it cannot be completely impartial because science (forgive the anthropomorphism) inherently disregards anything that is not based on its same assumptions and philosophies (e.g., religion). Science has one particular view of the world and states that everything else is false, or at least unknowable. That’s not impartial – that’s bias. That’s like Americans saying “Our world view is the only correct world view.” Now, maybe it is true but that does not make it less biased. Everything and everyone have biases, even the philosophies that form the foundation for science.

As I said, this is some pretty deep philosophy. People have been arguing over this for thousands of years and will be for thousands more.

One last example. We tend to believe that mathematics is perfect and unbiased. Kurt Godel showed that it isn’t. Now, not everyone agrees with his ideas but he convincingly showed that most math is flawed, or at least incomplete. Math does not equal science but most science is founded on mathematical principles.

I answered your question, hopefully without coming across as a troll. As I said in my original post, I’m not trying to discredit science (science is my job) but blindly accepting that science is perfect and completely unbiased and the only way to knowledge is demonstrating as much faith in science as many do in religion.”

After a reply back that expressed complete disbelief (that also insulted my intelligence) 🙂 here’s my final response:

“I did not say that philosophy and science are the same, I just said that science is based on specific philosophies. As I said, it’s some pretty heavy stuff that most people (rightly) don’t care about. Again, I didn’t say philosophy and science are the same. The relationship (and this isn’t a perfect example) is more like philosophy:science::arithmetic:calculus.”

Am I completely off base here? I haven’t had extensive epistemology but I’ve had a fair amount. I remember in one of my classes that some people just didn’t get it. They were very bright people, it’s just that philosophy requires a different way of thinking (not better, just different). It takes practice; I just happened to start having serious philosophical discussions with friends pretty early on in school.

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Neuroscience: Psychotherapy’s Executioner?

I wrote another post called Neuroscience: Psychotherapy’s Executioner? for BrainBlogger.com. You can read it here.

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Sen. Kennedy’s Brain Tumor

Sen. Ted Kennedy, one of the last of the siblings of JFK and Bobby who is alive recently was diagnosed with a malignant brain tumor in his left parietal lobe. His first symptom was a seizure. As soon as I heard that he had had a seizure I started wondering about a tumor. There aren’t too many reasons someone would have a seizure out of the blue at the age Sen. Kennedy is. Too much stress possibly could cause a seizure as could an adverse reaction to certain medications but those are not likely. Children often can have a seizure at random with no other symptoms or no specific underlying problems but it’s very rare for older adults to experience seizures without very specific reasons, such as a brain tumor (it’s very common to have seizures if you have a brain tumor).

Sen. Kennedy’s tumor, as stated earlier, is in his left parietal lobe. Depending on its specific location and size, the tumor could disrupt his ability to comprehend language (if it disrupts Wernicke’s Area). It could also affect his ability to integrate visual and motor information as well as affect his motor or sensory functioning on his right half of his body. All of those symptoms are speculative without neurological testing, of course, but the parietal lobes are involved in a number of functions, including sensory and cognitive integrative functions.

The good news is that this form of cancer – a glioma – does not spread to other parts of the body (although it could continue to grow in the brain). It is also treatable by resection and chemotherapy. Chemotherapy is far from an enjoyable process (it’s a treatment that practically kills people) but it can be very successful. While Sen. Kennedy’s prognosis is uncertain he could survive the cancer with relatively few lasting effects. I don’t think anyone can survive brain surgery and chemotherapy without at least some lasting cognitive deficits (although the deficits might be very hard to detect) but the outcome of gliomas is not always grim.

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On Vacation

I will be on vacation for the next 1.5 weeks and will not be updating the blog. Please visit any of the other websites in my blogroll or feel free to read some of my old posts.

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Finals

I’m in the midst of finals and will post when I’m able. Thanks for visiting the site. Please visit one of the other blogs in my blogroll. They are all excellent. I’ve also started writing some posts for BrainBlogger so I’ll have some articles appear over there.

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Frontotemporal Dementias

The New York Times has a very nice article about Frontotemporal demetia (FTD). This type of dementia is interesting, affecting personality, inhibition, attention, and language. It is similar to Alzheimer’s Disease but has a different progression and manifestation. Anyway, the article provides a nice picture of the disease.

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Frontal Lobes and Memory

I’ve been developing an interest in the role that the frontal lobes play in memory. We traditionally think of memory as heavily based in the medial temporal lobes. At least, the medial temporal lobes are larely responsible for the creation of new memories. Without the hippocampus and the surrounding area people have anterograde amnesia, which is the inability to form new memories. The classic and most well known example of this is the patient H.M. Researchers recognize the role that other areas of the brain have in memory but most memory research has focused on the medial temporal lobes – at least until recently (with recently being the last 20 years or so). New ideas take a while to develop and gain acceptance so some of these ideas about the role of other brain areas in memory creation are still developing.Man's Brain

For example, we now know that when information needs to be organized, such as in something like the Rey-Osterrieth Complex Figure (read here for a short description of the test) or with a list learning task with words from specific semantic categories, the frontal lobes are involved.

If the frontal lobes are heavily involved in the organization of information it follows that memory tests that require more organization of material should be affected by dysfunctioning of the frontal lobes. Some researchers are now trying to place certain functions with greater specificity within the frontal lobes. This isn’t really phrenology because the methods of phrenology were entirely suspect. Phrenologists extrapolated personality and cognitive characteristics of people based of measurements of their skulls. Many researchers who are interested in localizing brain functions do so by testing people with specific brain

lesions (injuries). If enough patients have damage to X part of the brain and subsequently have Y deficits, then we can assume that X is necessary for Y to occur (but is not necessarily sufficient for Y to occur). Phrenologists never looked at the brain or the head in this manner. Paul Broca was one of the first, with his patient Tan, to systematically look at the relationship between brain injury and behavior.

For a long time many people believed (and many still do) that certain areas of the frontal lobes, specifically the most anterior areas of the frontal lobes, are essentially superfluous. They base this idea on cases where

people have had damage to this area of the brain but apparently suffered no ill effects. Research has consistently not supported that view. We don’t have any non-necessary brain. What we do have are tests and measures that are not sufficiently sensitive nor specific. The brain is also very complex and most functions rely on networks of brain structures. We are also learning that the white matter in the brain is very involved in behavior and cognition (this is my own area of research). The more we learn, the more we realize our ignorance about the brain. There are layers upon layers to be unwrapped and understood about the brain.

Image by Debbi in California.

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Encephalon #42

I know I’m a few days late but Of Two Minds hosted the latest Encephalon. It’s a well-written collection of hot neuroscience geek writing. Although, I don’t understand how somehow the contributors all managed to miss the Douglas Adams connection with this Encephalon. The Paris Hilton thing was quite funny but this could have been THE ULTIMATE Encephalon, providing the answers to life, the universe, and everything. I, unfortunately, have not participated in an Encephalon yet but I’ll get around to it one of these days.

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UK Scientists Create Hybrid Embryos

Hybrid embryos were created in the UK. Scientists used bovine eggs that had the DNA removed and injected human DNA (from skin) into the eggs. The eggs grew for as long as 3 days. The researchers plan on working towards a 14 day lifespan, at which time the embryos would be destroyed. No, they aren’t trying to create a Minotaur or something of that sort; they are seeking for new ways to create stem cells. The researchers see this hybridization as one of the most promising ways. While the researchers on the team state that their research is completely ethical, a broader debate is occurring in the UK. If the research is completely ethical then there wouldn’t really be a debate. What’s ethical to one person is not necessarily ethical to another. Parliament will debate the issue in about a month. The Catholic Church, of course, has condemned the research.

It seems though that there are better ways to get stem cells that aren’t as controversial. I’ll admit that I am ignorant about this type of research but scientists already successfully can get stem cells from other sources, such as skin. There are very few people who believe that it is unethical to derive stem cells from such sources. I’m not saying whether or not I think that they should be doing this research I just think that those of us who are researchers think very carefully about the ethical and moral implications of our research. We can’t just seek consensus among fellow researchers either; we need to be willing to listen to people outside of science.

Read more about the issue here.

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