Karthik’s Web Blog

Last week when studying for my philosophy final, I came upon the “Design Argument” by William Paley. Paley cites the intricacy of the eye as one of the most incredible designs that the world has ever seen. How that even within species with advanced visual systems, depending on the medium of the light source the eye has been modified. For example, a fish eye must compensate for diminished strength of light underwater, and does so by having a higher degree of convex lens. Furthermore, there is no radial contraction of the iris, as there is never too much light to fall on the retina. He goes on to describe how no human creation will be as incredible as the devices found in nature.

While I have heard or read about some of the perceptual mechanisms used by humans, until this class I had not considered the immense behavioral and practical aspects of these complicated systems. In other classes we examined the “correct” anatomy and processes that allow us to perceive our world. However, only after I learned about the countless disorders of this system did I understand how intricate and important all of these components were. From the well-understood disorders, such as myopia and hyperopia, to those that are still being researched today, such as phantom limb, these disorders prove how many connections and mechanism must be intact just for what we deem as “normal”. However, this class taught me that “normal” requires immense amount coordination within our physiological systems.
I found the chapter on nociception and pain perception very interesting, because while pain is usually the indicator of other health problems; often pain itself is a disorder that requires intervention. One perceptual disorder, Phantom Pain, was especially intriguing to me as I have a family member who experienced it for numerous months. After a very unfortunate, yet life saving procedure, my grandmother endured amputations due to widespread sepsis, or the presence of bacteria and other toxins in multiple organ tissues. She has gradually recovered from these amputations and through hours of rehabilitation and commitment, has relearned to walk and perform other “normal” activities.
Immediately following the procedure, my grandmother experienced a burning, itching, and at times even a “deep muscle pain” in her phantom hands. I never really understood this pain, and attributed her condition to the nerve endings that were severed in the operation. However, after a more thorough description of the pain, it was clear that the pain was not coming from the stump, but rather the “hand” itself.

After reading about this independently and then again revisiting the subject in our class, I have learned numerous aspects about this disorder. Some of the first descriptions of phantom limb were first observed during amputations performed on the battlefield, by Ambroise Pare. More recently, V.S. Ramachandran has investigated this disorder and has had some very interesting findings, ranging from subjects who feel the heat of a coffee cup in their phantom hand to others that feel somatosensory sensations on the phantom hand when touched on the face! This phenomenon has had numerous explanations over the years, but one that has gained most recognition is that of “Cortical Remapping”. In the somatosensory neurons of the phantom area, fMRI studies have shown cortical remapping of adjacent somatosensory connections. Thus, in the case of the patient who experiences a manual (hand) sensation while shaving his face, the cortical representation of the face has shifted to the area of the hand. Thus somatosensory signal on the face will activate residual hand areas on the somatosensory cortex.

To explain the pain that is felt, there are numerous mechanisms that are being researched. Peripheral nerve injury has been shown to lead to an imbalance of innervations from C and A fibers in the dorsal horn. This imbalance, namely a relative increase in A fiber signals, has shown to be painful as the polypeptide neurotransmitter, Substance P, leads to increased activation of Nociceptors in the spinal cord.
Treatment plans, such as Deep-Brain stimulation and massage, are largely ineffective. However, one treatment method that has always impressed me is called the “Mirror Box”. The ingenuity of this method lies in ‘fooling’ your visual system. It entails placing both the normal and amputated arms within a box separated by a mirror. The mirror faces the real hand, and, thus, the subject views “two” hands. Even though the second hand is obviously a reflection of the real hand, the symmetry of our hands and the organization of the Mirror Box is such that the patient will actually feel as if he is moving ‘both’ hands. If the real hand is rotated and stretched, the patient remarkably experiences relief in the phantom hand! Hopefully more innovative and informed solutions to this strange condition will arise.

I apologize if this blog was a little more graphic than expected. Please do not confuse my openness with this subject with insensitivity to her condition. My family has had years to come to terms with the operation, and I understand if my introduction of the subject was a little abrupt. Phantom limb and the pain that can occur are very interesting and important problems in modern research. And, like other neurological disorders, such as the emotional transitions of Phineas Gage, it has actually lent information to the structure and function of our cerebral cortex.
References:

Randolph Blake & Robert Sekuler, Perception, Fifth Edition

<http://www-personal.umich.edu/~emcurley/paley.htm> April 27th, 2008

<http://www.mayoclinic.com/health/phantom-pain/DS00444> April 27th, 2008

<http://hubel.sfasu.edu/courseinfo/SL98/phantom4.html> April 27th, 2008

Since we talked about synesthesia in class, I have been really interested in the various permutations and causes of this phenomenon. While the concept of coupling many, if not every, perceptual stimuli with another of completely different modality seems complicated, it is used subconsciously everyday. I know that when I was learning math in grade school, I associated positive numbers with good and negative numbers as bad. For some reason I thought it was easier to attach an emotion to the impersonal numbers to make it more interesting. Furthermore, there are many colors in our commercial society that evoke certain emotional and even physiological responses. The following link lists out how colors can be used to effectively advertise your product click here.  Ones that really surprised me were Red and Orange as colors that promote hunger, which may account for many fast food logos containing red and orange click here. Another interesting color was Yellow which increases concentration, which is why it is used for legal pads and sticky notes.

But now this becomes a “chicken or the egg” dilemma. Have we imprinted red and orange to be associated with food and yellow with taking notes? Or does yellow actually make me pay more attention?  Surely, if the professor walked into class with a yellow rain poncho students have a tough time looking away.  But what is the origin this effect. A simple explanation to this phenomenon, would be that it is imprinted very early on. And we can imagine a person who associates the number 2 with the color green, may have had a poster in their kindergarten classroom that has the numbers 1-10 arranged with different colors, with the two being a nice bright blue, click here.  Furthermore, many example of synesthesia could potentially follow this model.  In the case of auditory cues evoking a particular emotion or image, it is very plausible for the brain to store even a small three-note melody and associate the sound with the emotion felt at that time.  We often make mnemonics and acronyms to help us condense and remember information, so it makes sense that we do that subconsciously with all stimuli.

While blindness and the many forms of visual deficits have been researched and well documented, there are many neurological deficits that also impair perception. One of the most fascinating disorders is called ‘Hemispatial Neglect’. In essence, a person ignores everything within one hemisphere of their visual field. Even though these patients have the visual processes and can see and recognize objects on the effected side, in practical life they cannot interact with anything on that side.
The first time I was introduced to this concept I could not understand how someone could see something but not acknowledge it. The “Phantoms of the Brain” video hosted by Dr. Ramachandran at UC San Diego discusses this phenomenon and gives good examples to explicate this disease. http://www.youtube.com/watch?v=_1RPkp7rdnw

Even when asked to draw something from memory, in object that they have viewed in both visual fields, patients with neglect will draw only the right side. In the video, a woman draws only the right side of a flower, and immediately recognizes her flaw after it is pointed out by the doctor.
One example that Ramachandran gave really shows how oblivious these patients are to their condition. He offers a paradigm to two different patients, one with an amputated left arm and one with left Hemispatial neglect. He lays in front of them a coffee mug and a long tray both filled to the brim with water. He tells them that they will receive $5 to pick up the mug and $10 to pick up the tray. The patient with the amputated arm, cursing the malicious doctor under his breath, picks up the mug as he has come to terms with the fact that he cannot use both hands to pick up the tray. The patient with neglect innocently takes the $10 dollar bet and bends over to pick up the tray. Ironically, even though the neglect patient has both arms intact, he only uses his right arm to pick up the tray and the water immediately spills off the left side of the tray.
While the exact cerebral areas have not been isolated, the most common case is right parietal lobe damage causing left-sided neglect (because of contralateral visual perception). This is thought to be so because the left parietal covers the right visual hemisphere, while the right parietal lobe partially covers both hemispheres. Thus damage isolated to the left side of the parietal lobe can be compensated by the right, but not vice versa.
So far, this bizarre and fascinating disorder has few pharmacological treatments. However, behavioral treatments such as putting the “good” arm in a sling or putting a patch over the unaffected side is used to encourage use of the neglected limb.
I found this chapter in “Crazy Neuroscience” (not a real book) very interesting because it showed yet again how crucial and intricate our brain is. While it seems like a bleak outcome for these patients, one optimistic view to look at disorders such as neglect is to realize that is behavioral as well as neurological. Therefore, these patients with just will power and commitment can slowly remediate their condition, unlike liver failure and other purely physiological disorders.
Sorry for the long post, hopefully now you will make sure to look both ways before crossing the road… even if you think there’s nothing there.

This year, for the first time in my life, I thought to myself “I’m getting old”.

I don’t understand how to use an iPhone, Fresh-Prince of Bel Air has a spot on Nick-At-Nite, and I’m increasingly impressed with the amount of fiber in Corn Flakes.

The other day, while I was perusing through the Hustler for coupons, I realized that I was having a hard time reading the newspaper. The vestigial “whipper-snapper” in me denied any visual deficit and refused to put on my glasses.   However, I have finally faced the fact that I need to wear glasses more often, and now carry them around all the time.  I first noticed visual issues during classes in high school that had a blackboard far from where I sat.  I was diagnosed with Astigmatism, a condition where the cornea is misshapen and light is distorted at at the retina.  I wore my glasses during class and take them off right after.  I was convinced that my vision was not horrible and that I would only need them to see far distances.  Furthermore, I was worried if I wore my glasses all the time, I would become dependent on them and my vision would get worse.

This year, however, I have noticed that I have kept my glasses on for most of the day.  I believe this is not because glasses have made my astigmatism worse, but rather that it has made the muscles that control my lenses weaker.  Analogous to a patient who wears a sling for a broken collar bone, the body part that is being assisted atrophies due to lack of activity.   The muscles around the lens flatten and thicken the lens, in the process of accommodation, to focus light onto the surface of retina.

Additionally, because the muscles around my lens are getting weaker, it actually is more strenuous to read without glasses.  I notice while I study late at night, that I actually have more energy when using glasses then when I am “eyeballing” it.  Thus, while I squint to see objects far away, when objects are close, my intra-ocular muscles are working overtime, and the strain is less noticeable.  Maybe, my astigmatism has always given me problems reading objects that are close, but, in my youth, my muscles were able to compensate.  In classrooms, I noticed immediately that my vision was poor because I would squint (using facial muscles) to read the board.  Squinting is much more apparent than overworking your ciliary muscles.  Only now, as I start receiving my AARP periodicals, are my muscles becoming stiffened with protein accumulation, making lens accommodation more fatiguing.

This past week within the heap of subservient undergraduate tasks that I perform in my research lab, I had the chance to explore an interesting component of the visual system. I work under Dr. Wallace, who is an authority on the subject of multisensory integration within the visual and auditory systems. The project that I am assigned to is trying to discover the differences in multisensory binding within varying stages of development. The general findings show that at younger ages humans will perceive a ’simultaneous’ event when auditory and visual information are separated over a larger temporal window than in adults. That is a ball can have a sound played after it hits the floor, and because infants have slower neurological processes (less myelin) and less visual experience, a baby will perceive that the sound was generated by the ball hitting the floor.

Look back at the three sentences of ramble that I just wrote, I realize that this seems like a verbose description of a very basic feature of our visual and auditory integration. However, deficiencies within this ability can seriously impair normal interactions and are associated with disorders such as Dyslexia and Autism.

My task was to help design a multisensory experiment to optimize attention among infant subjects by using certain stimuli. Previous studies show that children are more receptive to circles, the color red, and faces. An interesting study done by Teresa Farroni at Duke University, found that among faces, babies specifically prefer dark regions under the eyebrows and nose. During this experiment they tested the infant’s response to normal faces, a face with inverted colors, upside down faces, and crude smiley faces with normal or inverted coloring.

I found this very interesting because this is one way the brain compensates for the visual deficiencies of babies. Because they have slower conductions and less experience in terms of social/ inter-personal interaction, infants inherit a disposition/preference for this basic outline of the human face. This simple shading pattern (essentially a smiley face) represents the two eyes and the mouth.  This pattern is recognized by our visual system before our brain is fully developed and before we have socially learned the shape of the face.

The visual system has always intrigued me especially in the context of predator-prey evolution. From varying visual acuities within predators and prey to the anatomical position of eyes, the system is highly evolved in order to meet the needs of the organism. One visual component, the retinal ganglion cells, is present in both predators and prey as it allows for contrast and object border information.
This interesting system entails two distinct receptive fields: the center and the surround. Within these receptive fields, two different bipolar cells, on-center and off-center cells, exist. On-center ganglion cells are stimulated maximally when light is shown on the center portion of the receptive field. The on-center cell signal is weakened if light is also shown on the surround (a ring around the center field). If both sets of photoreceptors (center and surround) are not exposed to light or only the surround is stimulated, the On-center cells will be inhibited entirely. The Off-center cell response is exactly opposite, firing only when stimulated in the surround and weakened when a light stimulus is present in the center of the receptive field. In addition to a qualitative signal (fire or not fire), the Off-cells relay high and low frequency firing depending on exposure to light in the surround (high) or the surround and center (low). Thus a gradient of responses are given from these cells, depending on whether the segment each cell is responsible for is exposed to light. The Off-center cells are linked to the surrounding ring of the receptive field and thus will fire rapidly when light is shown on the surround, minimally when light is shown on both surround and center, but will not fire if only the center is exposed. The On-center cells fire in a similar fashion.
While this system seems convoluted, these cells serve an immensely important purpose. The center-surround arrangement allows the human eye to perceive distinct borders around objects and, more importantly to detect contrast or quick movements within the visual environment. Because each receptive field is small and is coded to a minute fraction of our entire scope of vision, the retinal ganglion cells are able to make excitatory or inhibitory decisions about each “pixel” of our visual input. Using an example of a bird flying across a bright background of sky; when the light signal from the bird crosses from surround to center, the cell firing will change from firing in the off-center to firing minimally in both on and off-center and finally to firing only in the on-center cells. Thus, within just one receptive field, of the many present in our system, we have a pattern of cell firing that codes to a certain movement. This benefits prey species who need to detect the slightest movements in their visual field (which is increased by placing eyes on the sides of their head), and also predators who need to have supreme acuity in identifying and measuring the distance of objects (prey).

    At the risk of admitting the extent to which I devour pop culture, the first time I was introduced to the concept of aphasia was during an episode of House.  The patient on the episode spoke rambled nonsense and was diagnosed with Wernicke’s Aphasia (speaking illogical sentences) and Agraphia (the inability to write rationally).  Being the omnipotent doctor that House is, he was able to replace the illogical words for what the patient meant to say and found a way to communicate.  While I am ignorant enough to believe a lot of the show (and the consequent hundreds of thousands of dollars in MRI’s) as plausible, I needed to investigate this peculiar neurological disorder for myself.

After reading about Wernicke’s (or ‘receptive’) Aphasia, I found that many of the references in the episode were accurate.  The disorder is often caused by a lesion or damage in Wernicke’s Area (Brodman Area 22) and has a profound effect if presented in the dominant hemisphere.  If it the lesion is in the non-dominant hemisphere the aphasia only effects the ability to perceive pitch, rhythm, and emotion in speech.   Thus, Wernicke’s Aphasia is characterized by the inability to understand words.  Unlike Broca’s Aphasia, where the patient has difficulty producing speech, patients with Wernicke’s Aphasia can not understand speech/language but speak fluently and as if they are making sense.

Patients with Wernicke’s demonstrate how crucial the process of auditory feedback is communication.  Similar to the case of deaf people, where they can not hear what they are saying and correct the phonetics of their speech, Wernicke’s patients cannot correct the actual words they use.  One example used when describing this disease is the inability to perceive the difference between words such as “bed” and “bad”.  Using this example it is easy to see how much of their vocabulary could be skewed, resulting in their ‘word salad’.   In the episode House interprets what the patient is saying and translates it into correct speech (one example was the word “bear” to “polar bear” to “bi-polar disorder”).  While the words are somewhat logically connected, the word “bear” and “bi-polar disorder” are not phonetically similar, which is believed to be the basis of Wernicke’s.  Thus, this scenario is a little absurd, and not exactly how a patient with Wernicke’s would replace words, but who am I to argue with House?

This past Friday, I witnessed something that shook my already feeble understanding of perception. A hypnotist at Dance Marathon proved in front of hundreds of people that your perceptions can be altered and that your body has little authority over your mind. Usually I am skeptical of the ‘volunteers’ that go up on stage and remarkably act exactly as the hypnotist commands. This time, however, I watched numerous Vanderbilt students (some of whom I knew personally and clearly not paid actors) engage in activities that their threshold for safety and or embarrassment would not allow. While the hypnotist admits that only certain people are susceptible to hypnotism, about 6 of the 25 or so volunteers that went on stage was significantly impacted by the hypnosis. One boy fell asleep while shaking the hypnotist’s hand, causing him to crash violently on his knees and side. The hypnosis had literally stripped him of his haptic senses and he allowed his body to a) lose balance and b) experience pain that is otherwise avoided by his reflexes. Later, a belt borrowed from the audience and the hypnotist told the volunteers before and after the prank that it was merely a belt. However, when he made hissing noises and shook the belt erratically, the volunteers apparently thought this belt was a snake and were terrified. One even went as far as shoving another volunteer in front of her to avoid being bitten by the obviously venomous italian leather belt. One of the most astounding ‘tricks’ was when the hypnotist told a boy to jump out of his chair and howl towards the moon. Without any hesitation, shame, or smirk on his face, the boy jumped onto his chair and howled like a genuine werewolf. Afterwards his episode, he immediately looked around and looked perplexed. When the hypnotist questioned him, the boy asked “Where did that howling noise come from?” This was one of the most intriguing aspects of the show, because it was concrete proof that the hypnotist had induced a top-down information processing and that the boy’s natural perceptual mechanics were rendered useless.

Immediately after I got back from Dance Marathon (and slept for an inordinate amount of time) I researched this phenomenon and found that this was no ‘magic trick’. Hypnosis is a certified by the American Medical Association and is found to affect 1 in 10 people! Later, when I recounted the events, it dawned on me that the only common factor was that all the stimuli were given orally. Whether it was the command to ’sleep’ or an innate association with hissing noises and snakes, these volunteers were shunning all of their normal perceptions in order to replace them with the hypnotists suggestions. While this seems like a neurological flaw, it is said that susceptibility to hypnosis is related to one’s ability to imagine and not their intellect. For me it clarified a seemingly obvious point in neuroscience; the brain could not only receive perceptions and create movement in body parts, it could effectively create perceptions and actually abide to them more closely than actual external stimuli.

This related exactly to the way songs get ’stuck in my head’ or how if a song is stopped I can ‘hear’ the next seconds or even minutes of the song just through memory. Essentially all of the incredibly advanced physiological mechanisms of perception (i.e. the auditory, visual, and somatosensory systems), are merely suggestions for what you perceive. Ultimately, your mind controls you, not the other way around.

    This past week, I finally got a chance to use the plastic reinforcement rings I bought in middle school.  The taste bud experiment answered some long-unanswered questions and was fairly simple, even though my friends were not too excited about me inspecting their mouth like a judge at a dog show.

Among my friends I have a reputation for applying preposterous amounts of hot sauce on just about everything I eat. Furthermore, I’ve noticed that I never eat as much as my friends during an average meal. After performing the experiment, I found that I have fewer taste buds than most of my friends; 13 vs an averaged 20. While that does not seem like a very large difference, if the count from small area contained within the sticker were to be extrapolated to the entire tongue, it would be a very large difference in total fungiform papillae.

After collecting this data, I hypothesized that the reason I can tolerate, and therefore, enjoy such spicy foods is because I have less papillae than others. However, after reading the chapter I learned that the ‘hot’ component of spicy foods is capsaicin (and capsaicinoids) which activate pain receptors, not taste buds (papillae).  Pain receptors (free-nerve endings) may have some positive correlation with the number of fungiform papillae, but this wasn’t reason for my dousing every meal with Cholula.  I think my propensity to eat hot foods is environmental, if not genetic.  I have grown up eating spicy foods with my family, and my senses have adapted and accustomed to this unique perception of pain.  Furthermore, my dad has always jokingly hinted at the fact that I couldn’t eat the spicy foods he ate until I was as much of a ‘man’ as he was.  For much of my life, I have respected and sought the approval of  my father. This may just be a very minute, and admittedly bizarre, testament of my respect for him. Furthermore, this emotional association may also be connected my (previously) subconscious desire and appetite for hot foods.   Its funny that while I write this, I am now questioning how many subconscious impulses I have that adhere with my desire to be like my father.

Aside from my more psychological realization, I also learned through various sources that spicy foods are somewhat of an appetite suppressant and metabolism-booster.  While the suppressive aspect could be explained simply by dulling the taste sense or the physical pain, the increased metabolism is more thoroughly researched.  The ‘hot’ sensation of spicy foods actually causes your body to increase the body’s temperature and, thus, expend more energy.   While I am sure my lean physique is more complicated than just these two aspects, it is interesting that my love of spicy foods could be the reason that i a) do not eat much at a given meal and b) have a slightly higher metabolism.

Before thinking about this blog, I would have never thought the taste sense could have such a profound impact.   While I can’t prove this quantitatively, it is remarkably plausible for this strange perception to be connected with my recreational, emotional, and even physiological characteristics.

Over the last week as I practiced my guitar, my body encountered a familiar wrist pain that has fluctuated in severity since 9th grade.   A couple of years ago a doctor explained to me that this was called “tendonitis” and that it is essentially swollen tendons within my left wrist.  Caused probably by some combination of football, wrestling, and overzealous high-fives, I have managed the pain using Motrin, Tylenol, and in times of severe pain, a cortisone injection.  The cortisone injection indirectly ameliorates the pain by reducing the swelling of the tendons. This is a very common problem, and admittedly one of the more mundane procedures of an orthopedist’s repertoire.

I experience some sensation of pain everyday, and in most cases the physical/mental aspect of pain is overshadowed by my considering the alternative.  Pain helps me avoid harmful circumstances, alerts me when something in my body is awry, and, when I exercise, gives confirmation that my muscles are going through the natural process of tearing and restoration that results in muscle gain.

However one aspect of pain that I have only recently questioned is the internal pain.  While external, or cutaneous, pain received by free nerve endings signifies a harmful stimulation (fire, sharp objects, electricity etc.), internal pain can not effect an alleviating action by the person experiencing the pain.  If one steps on a tack with their left foot, the person can avert their weight to their other foot before the tack causes serious damage.  However if a deep visceral pain is felt, how is one expected to respond? From an evolutionary perspective (considering a time when one can not call an ambulance) what is the physiological necessity for free-nerve endings surrounding the heart? Stomach? Or spleen? While today if these sensations should occur, the person would seek medical assistance and treatments to isolate and reduce the pain.  In the days of early humans, what was the evolutionary reason for this horribly inconvenient perception?  While we will never know what our mad-scientist of a god is up to, I can only imagine that pain before the advent of doctors and medicine was used a societal tool.  That is, the person receiving pain was made an example of to the rest of his community: The unfortunate hunter-gatherer who first ate raw meat and got sepsis, the curious child who ate poisonous berries, and the swimmer who became a host to the neighborhood tape-worm; all merely martyrs in the advancement of human knowledge. How else would we have learned to cook our meat, avoid poisonous foods, and stay out of certain bodies of water?  Definitely a morbid thought, but it made me appreciate the fact that when I have pain, people around me can take action, instead of just scratching their heads and grunting.