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Biology 202, Spring 2005
Second Web Papers
You are at the park, and a child comes running up to you. You have never met her before, but she displays a familiar friendliness as if she's known you all her life. She's only three years old, but she has an amazing way with words that adds to her remarkable sociability skills and engaging personality. It's not obvious at first, but when you take a closer look at her, you notice distinctive physical traits. When you look into her eyes, she has a star-shaped iris with full periorbital surroundings. Aside from her eyes, she has a full nasal tip and flattened nasal bridge, a wide mouth with full lips and cheeks, a long indentation in the midline of her upper lip, and a small jaw. This child has Williams Syndrome.
People with Williams Syndrome function in the mild range of mental retardation, and they possess IQs averaging about 60.(1) They have a distinctive neuropsychological profile that includes strengths in face perception, affective attunement, short-term auditory memory and select aspects of language, along with weaknesses in visuospatial, motor, visuomotor integration, and arithmetic skills.(1) It is hypothesized that the diverse brain regions and its variations account for different functions within larger networks provide the physiological bases for the specific strengths and weaknesses found in Williams Syndrome. Their display of strengths and weaknesses of uneven cognitive profile and atypical parts of specific areas of the brain is one of the reasons that make the study of Williams Syndrome so interesting for me.
Williams Syndrome is caused by a small genetic deletion on the long arm of chromosome 7, encompassing approximately 25 genes.(2) This deletion codes for four genes that are highly expressed in the brain, FZD9, STXIA, LIMK1, and CYLN2. In addition, the whole brain volume is about fifteen percent smaller than normal, but the superior temporal gyrus, an area that encompasses primary auditory cortex, is of approximately normal volume.(1) Preliminary structural MRI evidence suggests an exaggerated leftward asymmetry of the planum temporal gyrus.(1)
As mentioned briefly before, people with Williams Syndrome possess a heightened interest in music and preserved language abilities. The language of individuals with Williams Syndrome sometimes seems precocious in their use of unusual words and conversational flourishes. (3) These strengths may be due to their neurological traits of the brain structure. Although it is smaller as a whole, a small study using auditory event-related potential found increased amplitude of early endogenous components suggesting hyperexcitability of the primary auditory cortex.(1) And it might be their alterations of the function in this area of the brain that may explain the rate of hyperacusis and language/music perceptual processes. Also, the planum temporale has been linked to hemispheric dominance for language. In musicians with perfect pitch, there appears to be even more pronounced leftward asymmetry of this region, like that of a person with Williams Syndrome.(1)
Despite these strengths, they also have profound visuospatial weaknesses. They have difficulties visualizing the spatial relationships between objects, their distances and overall configuration. They have particular weaknesses in dealing with numerical concepts, spatial cognition and in abstract reasoning.(3) In the mid-1990's, these deficits of visuospatial abilities was linked to the deletion of L1MK1, one of the four brain-expressed genes. However, further studies have shown that deletions involving this gene still displayed an intact spatial ability.(1) This goes to show that there may not be one easy answer to explain a certain deficit or even a strength. It might just be specific combinations.
The functional segregation of visual processes in the brain is split by visual domain into a dorsal stream that connects the occipital cortices and the parietal love and a ventral stream of information flow from the occipital to the temporal cortices.(1) Although this disorder causes spatial deficits, it seems to play a positive role in face perception and recognition. The fusiform gyrus, a region on the underside of the temporal lobes, seems to have a specific role in face perception. Specifically, the presence of the anatomical connection between the fusiform gyrus and limbic areas of the brain may be responsible for many emotional processes that function for face perception.(1)
There may also be a connection with high face perception and social-cognitive skills. It is believed that being able to have keen face perception and understanding the emotional states of others through facial cues may be closely tied to social-cognitive skills and the ability to form and maintain social relationships.(1) This hypothesis is supported by a study with autistic people, who display a lack of interest in social relationships, seem to fail to engage the fusiform gyrus during face perception tasks.(1) While there is no activation of this region for autistic people, individuals with Williams Syndrome seem to have normal use of the fusiform gyrus for face perception. In other words, levels of fusiform gyrus activation can be related to levels of social relatedness. If this is true, in normal brains, can we account for personality differences in sociability to the way our brains, specifically the fusiform gyrus, reacts? And can we say generalize this hypothesis to say that people who are keen at face perception and recognition have higher sociability skills?
This concept of connecting the fusiform gyrus to social relatedness may not work for normal brains and personality traits. In terms of brain studies, it was found that face recognition in healthy adults was associated with scalp voltage waveforms are predominantly localized to the right hemisphere. In contrast, ERP's in adolescents and adults with Williams Syndrome were found to be distributed across both hemispheres and did not distinguish between human faces, monkey faces, and cars.(3) In normal brains, the cortical specialization for face processing observed in normal adults is achieved through gradual experience-driven specialization of an initially more general-purpose visuo-spatial processing system. However, in Williams Syndrome patients, genetic effects during brain development generate initial cortical structures with different neurocomputational biases which yield an overall processing that is poorer but have circuits with greater potential to process isolated features than configurations.(3)
There have been numerous tests to better understand the ways in which individuals with Williams Syndrome display certain weaknesses and strengths, especially in recognizing faces. There seems to be increasing evidence, however, that the ways in which people with this disorder process incoming stimuli may be atypical compared to that of a healthy adult. Then does that mean that it is possible to be good at certain tasks when using abnormal processing mechanisms? This first peek through the window of the mind and brain progression of an individual with Williams Syndrome has revealed that nothing is simple or direct.
1)Journal of the American Academy of Child &Adolescent Psychiatry
2)Stanford Psychiatry:Neuroimaging Laboratory
3)Williams Syndrome: Fractionations all the way down?
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