The cerebellum has an established role in low level cognitive functions such as attention, balance, timing, coordination, and motor abilities. Recent functional imaging and lesion studies suggest that the structure may also modulate higher cognitive operations such as language, affect, memory and spatial abilities. This dissertation examines the size of the cerebellum relative to performance on high and low level cognitive tasks in Williams syndrome (WS), a rare genetic disorder involving mental retardation and a distinct neuropsychological profile. The disorder is used as a model to better understand the role the cerebellum plays in cognition.;Three studies were conducted. Study 1. Twenty-two adults with WS (mean age 27 years) participated in magnetic resonance brain imaging (MRI) and a series of neuropsychological tests. Principal component analysis was used to reduce the number of cognitive variables; the resulting composite variables were examined relative to midsaggital surface area measurements of cerebellar, parietal, occipital, cingulate, and callosal brain areas. Surface area of the neocerebellum was moderately correlated with behavioral performance on syntax (r2 = -.45)and object recognition (r 2 = -.41) tasks, but there was no relation between the size of neocerebellar regions and other aspects of cognition. Neocerebellar regions uniquely accounted for 16% of variance in syntax scores (p = .07) and 17% of variance in object recognition scores (p = .07) above and beyond the contributions of total cerebral surface area, age or gender. There was no relation between syntax and object recognition variables and other measured brain regions.;Study 2. Performance on a visual-attention paradigm was examined in twenty-four adults with WS (mean age 28 years) relative to four control groups. Subjects with WS showed deficits on all indices relative to same-aged normal controls. They also showed deficits on orienting and validity effects relative to mental-age matched controls, but showed relative strengths on other task indices. Occipital surface areas as measured from MRI showed a mild negative correlation with the orienting effect (r2 = -.34) and accounted for 23% of unique variance in orienting scores above and beyond total cerebrum surface area, age and gender. Cerebellar and other region surface areas did not account for unique variance in orienting or validity scores.;Study 3. Clinical MRI scans of nine toddlers with WS (ages 7 to 43 months) were examined relative to nine age and gender-matched normal controls. Two neuroradiologists blinded to subject diagnosis and brain regions of interest sorted the scans based on six neuroanatomical criteria. The WS subjects were consistently sorted into the abnormal category only when the raters attended to features of the cerebellum, suggesting the cerebellum is abnormally large beginning early in development.;The results of these studies demonstrate a general role for the cerebellum in higher cognition that can be detected using WS as a model.
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