FINAL BLOG ENTRY

The most fascinating thing I learned this semester was undeniably about the rare condition of synesthesia. Synesthesia is a condition in which sensory stimulation evokes an experience ordinarily not associated with that stimulation. The form of synesthesia we focused on during color perception, called color or orthographic synesthesia, is the condition in which colors are experienced when viewing black or white letters or numbers.

Individuals with synesthesia tend to be distinctive or individualistic in their experiences, but these experiences are consistent for them throughout their lifetime. Even more interestingly, new research highlights the fact that a particular commonality exists across these synesthetes, who otherwise have very unique experiences. Psychologist Daniel Smilek and his colleagues at the University of Waterloo have found that a relationship or association exists between how frequently a synesthete uses a given digit and the brightness of the synesthetic color experience. They have found that the more frequently letters or numbers are used, the more luminous the synesthetic colors are for that person.

Additionally, the team of researchers found that this relationship is not bound to synesthetic color experiences. When non-synesthetes were asked to choose colors to associate with letters or numbers, the non-synesthetes also selected more luminous colors for digits and letters used more frequently in daily activities. However, the relationship between letter and number frequency and color luminance was much weaker for non-synesthetes than the synesthete individuals. With this evidence, Smilek now believes that these color associations made naturally in synesthesia may be tied to normal cognitive processes in the brain. The full article can be found at: http://www.sciencedaily.com/releases/2007/09/070918161553.htm

But how and why do these synesthetic sensations occur? How does stimulation of one sensory pathway lead to automatic and uncontrolled experiences in a separate and distinct sensory pathway in the brain? Researchers believe that the answer may lie within the ventrolateral nucleus of the thalamus. It has been found that the ventrolateral nucleus of the thalamus, usually involved in motor functioning, plays a part in sensory processing as well and that damage to this brain region leads to functional and neural modifications.

Tony Ro and his team of researchers at Rice University conducted a series of behavioral and neuroimaging studies on a patient who had suffered a stroke affecting only the right ventrolateral nucleus. Following the stroke, the patient experienced a dramatic change in her sensory perception: when she witnessed specific sounds, she felt sensations in the left side of her body, especially in her left arm. The bodily changes she experienced also evolved over time, growing in intensity as time passed. The results of Ro’s experiments from this case study suggest that the VL lesion resulted in a significant amount of functional and neural reorganization in the brain that influenced her sensory perceptions.

These findings demonstrate that acquired forms of synesthesia may appear months or years following brain damage. According to Ro, “Regardless of the exact neural mechanisms, this phenomenon of brain-damage induced feelings of sound suggests that other forms of synesthesia, in which reportedly neurologically normal individuals feel, taste or see something qualitatively different than the actual sensory input, may be due to cross-wiring in the brain, especially subcortically.”

The results suggest that connections between the thalamus and other brain regions may be important for the capability of the nervous system to alter in terms of sensory processing following brain damage. With their findings, the researchers concluded that the disturbances within the thalamus caused changes in the connections between the auditory and somatosensory cortex leading to the patient’s synesthesia. The full article can be found at: http://www.sciencedaily.com/releases/2007/09/070924072449.htm

I believe that this psychological phenomenon of synesthesia is completely fascinating. I think it would be fabulous to live with synesthesia; that is inherited synesthesia of course, as opposed to synesthesia resulting from VL thalamic brain damage. Synesthesia can be seen as extremely adaptational and beneficial for humans. Since synesthetes have a higher level of perception they can use this advantage in cognitive tasks such memorization or searching for hidden geometric patterns. This rare but interesting condition can provide immense insights to human perception today as well as in the future. Additionally, case studies like the one presented above provide tremendous insight into the consequences of VL thalamic brain damage.

Judging Depth with One Eye

As we discussed during Professor Boucher’s lecture, depth perception is the ability to perceive the three-dimensional locations of objects in relation to the perceiver’s position in space. Depth perception also allows a perceiver to separate objects from their backgrounds and to discern the three-dimensional shapes of objects. Although depth perception relies primarily on binocular cues, it also uses monocular cues to make judgments. After a vigorous search for how the brain judge’s depth with a single eye, a team led by Greg DeAngelis from the University of Rochester believes it has found the answer scientists have been searching for. DeAngelis and his team believe that this task is accomplished in a small region of the brain that processes both the image from one eye and the motion of our bodies.

According to DeAngelis, “It looks as though in this area of the brain, the neurons are combining visual cues and non-visual cues to come up with a unique way to determine depth.” The brain is comprised of many neurons that measure our motions and how objects move in relation to one another to create the appearance of three-dimensions. This finding in neural processing is based on the idea of motion parallax: a source of monocular depth information based on the difference in motion between images of objects located at different distances from a viewer. According to motion parallax, when looking at a stationary object, any motion we make will cause things closer than the stationary object to appear to travel in the opposite direction, and more distant objects to appear to travel in the same direction.

In addition to motion parallax, the motion of the eye ball itself helps to create this three-dimensional image. If the eye is moving while tracking or following the movement of objects, it provides neurons in the brain with information to understand that the object moving the fastest in the same direction must be the closer object and that the object moving the slowest must be further away. Hence, our own motion plays a large role in creating a three-dimensional image in our brain.

These new findings are remarkable and may be extremely important for future advancements in visions research. Children born with vision impairments may be able to recover normal binocular vision with information from these new developments. In addition, since it is now known how the brain forms three-dimensional perceptions, virtual reality games may become even more realistic in the future. The full article can be found at: http://www.sciencedaily.com/releases/2008/03/080316161128.htm

Color Vision Vs. Motion Detection?

After discussing color perception during Professor Boucher’s lecture I thought it was be interesting to further investigate the vision system used to process color.  According to findings by researchers at New York University’s Center for Developmental Genetics and in the Department of Genetics and Neurobiology at Germany’s University of Wurzburg, the color vision system has been discovered to be independent of motion detection in eye sight.  These findings are extremely important because they are in opposition to and contradict previous results that suggested motion detection and color contrast work together in association.  Since color is believed to increase the clearness of objects, these new findings seem to be incongruous.

It has been a heated debate whether motion vision uses color contrast in eye sight, and as a result has been studied in several animals and humans.  Until now, it has long been believed that color and motion operated and were processed together.  To test the controversial issue, the researchers studied the fruit fly Drosophila and its eye responsiveness to moving color.  They compared the results of normal flies to groups of mutant flies; half the mutant flies lacked photoreceptors for motion detection while the other half lacked photoreceptors for color processing.  The results reveled that flies missing the photoreceptors for detecting color displayed the same ability to detect motion as the normal flies.  From these results, the researchers concluded that the vision system used to process color is separate and does not contribute to the vision system used to detect motion.  

These findings are extremely important for the field of vision research.  Although the results revealed that color is excluded from processing motion in fruit flies, further researcher needs to be conducted to determine whether the two systems work in complete separation, or maybe even in opposition, in other species as well.  The full article can be found at:  http://www.sciencedaily.com/releases/2008/03/080319114627.htm

 

 

A Stable World

As we have been discussing over the past few lectures, eye movements can be both voluntary and involuntary aiding in acquiring, focusing, and tracking visual stimuli. These eye movements occur several times per second and when we change or relocate our eye gaze, we draw our attention to a new stimulus.

According to a new study originating from the University of Munster in Germany, this shift in our visual attention creates a temporary consolidation of our visual space. The researchers have found that before we change our eye gaze, a brief shift of attention towards the new target stimulus occurs so that visual processing at the target location improves before the eye itself witnesses it. This earlier action by our attention increases the sensitivity of visual neurons in the brain, which in turn respond more intensely to the target just before our eyes move. In essence, eye movements are used to enhance the neural representation of the stimulus positioned at the future eye location.

The researchers used a neurological model representing the visual area to study the costs of these alterations in sensitivity. In the search for how spatial location changes, they found that stimuli shown just before the eyes moved actually lied at the gaze target rather than at their actual spatial location. Hence, there was a consolidation of visual space.

This demonstrates how neurons in some of the visual brain areas seem to move their receptive fields; they change the direction in which they respond prior to the movements of the eyes. When all of these changes in each of the receptive fields are combined, the brain can now process visual information around the new target stimulus. With these changes we can now see the characteristics of the target object before actually looking at it. According to the researchers, “this increase in processing capacity makes the world appear stable while we move our eyes.”

These new findings are remarkable and may be extremely important for future advancements in visions research. The full article can be found at: http://www.sciencedaily.com/releases/2008/02/080215103316.htm

 

Ekman’s Basic Emotions

As we discussed during Professor Boucher’s lecture on Wednesday, the detection of negative facial expressions is faster, easier, and more efficient than the detection of positive facial expressions in visual search tasks involving collections of faces. We concluded that this is true because being able to perceive and detect negative faces has an adaptive value. For example, fear tells us to run away because threat is looming (the fight or flight response). In talking about the facial expression of fear, we also discussed Ekman’s six basic or primitive emotions. Besides fear, Ekman has found evidence for the universal expressions of anger, disgust, happiness, sadness, and surprise. These basic emotions serve different adaptive functions and allow rapid responses to biologically relevant stimuli. Ekman’s work provides evidence that in humans, these expressions are specifically expressed and recognized cross-culturally.

 

Ekman’s evidence for the universal expression and physiology of the six basic emotions suggests that there indeed exists a biological origin. In other words, emotions are a product of evolution. Ekman claims that all humans, across all cultures create and express the six basic emotions in the same way. Specific facial muscles are involved in expressing and conveying specific emotions. For example, the narrowing and tightening of the margins of the lips is evident only in the expression of anger. According to Ekman (1992), “only one muscle is needed to signal disgust clearly (levator labii superioris, alquae nasi, which raises the nares, pulls up the infraorbital triangle, and wrinkles the sides of the nose), and that muscle action does not occur systematically in any other emotion” (p. 3). Additionally, the zygomatic muscle that pulls the lip corners upward signals happiness but when it occurs in conjunction with other muscles it signals sadness. A table compiling the motion cues and muscles involved in the expression of each of the six basic expressions can be found at: http://www.nbb.cornell.edu/neurobio/land/OldStudentProjects/cs49095to96/hjkim/emotions.html

 

Ekman has also found emotion-specific autonomic nervous system activity for the basic emotions. So far, distinct patterns of ANS activity for sadness, anger, fear and disgust have been found. In both young and old subjects, the same emotion-specific patterns in heart rate and skin conductance were found when these specific emotions were elicited. In addition, across cultures these findings have been replicated. Ekman believes that specific ANS activity has only been found for these four so far because specific action tendencies and motor activities are associated with these emotions for survival. For example, anger informs us that we are upset and to respond forcefully, fear tells us that something is wrong and we should run away, and disgust tells us to expel something from our bodies to avoid potential harm. Regardless, Ekman is convinced that specific physiological patterns will be found for the other two basic emotions of happiness and surprise very soon.

 

Reference: Ekman P. (1992b). Are there basic emotions? Psychological Review. 99, 550-553.

 

Fixing Monocular Vision

As we have been discussing during Professor Boucher’s lectures on vision, binocular vision is vision in which both eyes are used together. This type of vision provides us with precise depth perception and enables us to accomplish intricate visual processing. Although it is exceedingly rare, some individuals do in fact see better with the use of only one eye.

In researching treatments for vision disorders in which individuals see better with only one eye, MIT scientists claim they have found the gene responsible for binocular vision. Researchers from the Picower Institute for Learning and Memory at MIT have located this gene involved in combining information and creating matched projections from the two eyes into one cohesive image in the brain. The MIT scientists have revealed that this gene, Ten_m3, plays an essential role in the early development of brain pathways for vision.

During research trials, investigators knocked out the Ten_m3 gene in mice to study the effects of the missing gene. It was found that in the mice with the missing gene, projections from their two eyes were backwards or mismatched in their brains. Since each eye’s projection stifles the other, the mice became blind. During additional trials, researchers found that when the output of one eye was blocked, the knockout mice could actually see again. This occurred because when one eye’s mismatched input was cut off, the other eye was able to function again. Since only one eye was able to function, these mice could see only with monocular vision.

Visual disorders are often found in humans when the Ten_m3 gene is affected. Finding a cure to these disorders will involve extensive genetic manipulation and research with the Ten_m3 gene. Researchers are confident a cure will be found in the future! The full article can be found at: http://web.mit.edu/newsoffice/2007/sightgene-0913.html

Saving the Retina

Researchers at the University of Washington have successfully used human stem cells to treat diseased parts of the retina in the eyes of mice. Previously, diseased parts of the retina had been treated with stem cells from mice, but this was the first time human stem cells had been used in the procedure.

After growing the embryonic cells in the lab, the scientists placed them in a combination of growth factor proteins. The most difficult part of the research was finding the right grouping of growth factors. They finally discovered a combination of growth factors in which the cells developed into retinal antecedent cells about twice as fast as they would have in the uterus. These newly developed cells then replaced damaged cells in the retina.

Successfully manufacturing cells that develop into retinal cells is a major step in treating eye diseases. The scientists anticipate that this might lead to a healing for human retinal diseases, including macular degeneration. In the future they hope to transplant stem cells into blind animals and see if the blindness can be cured. Discovering treatments for the eye with the use of stem cells is also extremely important because it may provide essential knowledge about how to treat the degeneration of other neural tissues. Since the retina is an extension of the nerves in the brain, what is successful for the retina might possibly be successful for brain or spinal degeneration as well. The full article can be found at http://seattletimes.nwsource.com/html/health/2003199363_retina15m.html

 

 

The Eyes and Diagnosing Disease?

After discussing eye movements during Professor Boucher’s lecture, I was curious to investigate the connection between eye movements and psychiatric illness, specifically schizophrenia. Do developmental changes in the brain affect eye movement controls, and if so, what happens in individuals suffering from disease? Researchers are currently investigating how irregularities in eye movements may be used in the future to diagnose psychiatric diseases. They have found that abnormalities in how the eyes track a moving object is caused by problems with neurons and their connections in the brain. Specifically, researchers have found that schizophrenics have trouble keeping their eyes focused on slow-moving objects.

Researchers claim that new technology for eye movement tests will better investigate abnormalities in the brain that are causing eye movement disturbances. Although a noninvasive and safe procedure is still underway, it is hoped irregular eye movements can be measured and compared with people who have normal pattern eye movements. John Sweeney, director of the Center for Cognitive Medicine in UIC’s department of psychiatry, and colleagues have been testing eye movement patterns in patients with Schizophrenia and hope to prove that eye movement abnormalities are factors for diagnosing brain diseases. During their studies, test subjects participate in 90 minute series of visual tests designed to test the function of different parts of the brain controlling cognitive processes and eye movements. Additional tests are also completed in MRI scanners, allowing experimenters to observe spatial and temporal brain activity.

Attempting to link irregular eye movements and cognitive problems with genes, Sweeney and his team look forward to identifying high-risk individuals and in effect, prevent the onset schizophrenia and other serious brain disorders that can be avoided. The full article can be found at: http://www.schizophrenia.com/New/Oct2003/eyemove.htm

Damaging Your Own Brain?

As Professor Boucher discussed during lecture, Wernicke’s area is important for language comprehension while Broca’s area is essential for speech production. We also learned that these two brain areas are connected by a bundle of fibers known as the arcuate fasiculusus and that damage to this pathway can cause conduction aphasia. In conduction aphasia auditory comprehension is preserved, but it is difficult to repeat heard speech and meaningless fluent speech is usually conveyed. With this is mind, I was curious to investigate the connection between Schizophrenic patients, characterized by disorganized speech, and damage to these brain regions.

Dr. Hubl and colleagues at the University Hospital of Clinical Psychiatry in Bern, Switzerland have found that changes in the white matter fiber tracts of the arcuate fasciculus may cause the auditory hallucinations that Schizophrenic patients experience. During inner speech, these alterations in white matter lead to abnormal activation in brain regions related to speech perception and hearing, making it difficult for patients to distinguish internal thoughts from external events. Since there is a disturbance in information between brain regions associated with hearing and language, a disturbance in the stream of speech occurs. These abnormal connections lead to abnormal activation causing internally generated speech to be perceived as external. Hence, hallucinations occur. The full article can be found at: http://www.neuropsychiatryreviews.com/aug04/npr_aug04_auditory.html

On that note, it has been found that people can actually harm their own arcuate fasciculi. Researchers have discovered that adolescents who continually smoke marijuana put themselves at risk for damaging the arcuate fasiculusus. The damage to the brain caused by smoking marijuana is the same damage that appears in the brains of Schizophrenic patients. Dr. Ashtari and colleagues from New York Albert Einstein School of Medicine used a technique called diffusion tensor imaging to look into the brains of adolescent marijuana smokers, adolescent schizophrenic patients, and healthy non-drug using adolescents. The investigators found that recurring exposure to marijuana was related to abnormalities in the development of the arcuate fasciculus associated with higher aspects of language and auditory functions. Additional experiments comparing developmental outcomes for healthy adolescents, schizophrenic patients, and marijuana users have revealed that no abnormal development changes were seen in the language pathways of healthy adolescents, but that abnormalities were seen in both the marijuana users and schizophrenic patients. According to Dr. Sanjiv Kumra, “These findings suggest that in addition to interfering with normal brain development, heavy marijuana use in adolescents may also lead to an earlier onset of schizophrenia in individuals who are genetically predisposed to the disorder.” The full article can be found at: http://www.schizophrenia.com/sznews/archives/002708.html.

If Bats Can Do It…

I thought it was particularly interesting when we discussed bat sonar during Professor Boucher’s lecture on the auditory system. I was always curious as to how bats, usually living in dark areas or caves, are able to fly in complete darkness and swoop down and snatch their prey without warning. As we discussed in class, by emitting high-pitched sounds and listening to the echoes known as sonar, bats are able to locate their prey and other nearby objects. During this process of echolocation, the bat’s head is continually moving, searching for things around it and sensing the time and direction of the returning sound waves. When the waves return to them they are able to map out the target object’s location. If an echo comes in faster in a particular area then they know that the object is near.

 

So why can we humans not hear the pulses of a bat’s sonar? Dr. Donald R. Griffin, who coined the term “echolocation” in 1944, stated that the sounds bats use to navigate are ultrasonic, too high pitched for our human hears to distinguish. To study this phenomenon, Dr. Griffin assembled a special microphone and attached it to a cathoderary oscillograph. Each pulse emitted by the bat made a measurable pattern of light on the screen. Hence, although we cannot hear them, the pulses of a bat’s sonar are tremendously loud. If human ears were tuned to bat frequencies, a bat flying near one’s head would sound as loud as a “fighter airplane” claims Dr. Griffin. (http://www.time.com/time/magazine/article/0,9171,812332,00.html?promoid=googlep)

 

According to ScienceDaily, the Office of Naval Research hopes its team of researchers will be able to do echolocation as bats can do. Just as bats use sonar to locate their prey and steer clear of obstacles, the military would like to find and detect submarines and mines in the same fashion. Neuroscientist Jim Simmons claims, “We want to know what the neurons in the bat’s auditory system are doing to process the echoes that allow their brains to ‘see’ an image.” Hence, getting naval sonars to become more bat-like would be extremely advantageous for anti-submarine warfare. The full article can be found at http://www.sciencedaily.com/releases/2002/04/020429073532.htm.