Language dominance and factors that influence language lateralization were investigated in right-handed, neurologically normal subjects (n = 100) and right-handed epilepsy patients (n = 50) using functional MRI. Increases in blood oxygenation-dependent signal during a semantic language activation task relative to a non-linguistic, auditory discrimination task provided an index of language system lateralization. As expected, the majority of both groups showed left hemisphere dominance, although a continuum of activation asymmetry was evident, with nearly all subjects showing some degree of right hemisphere activation. Using a categorical dominance classification, 94% of the normal subjects were considered left hemisphere dominant and 6% had bilateral, roughly symmetric language representation. None of the normal subjects had rightward dominance. There was greater variability of language dominance in the epilepsy group, with 78% showing left hemisphere dominance, 16% showing a symmetric pattern and 6% showing right hemisphere dominance. Atypical language dominance in the epilepsy group was associated with an earlier age of brain injury and with weaker right hand dominance. Language lateralization in the normal group was weakly related to age, but was not significantly related to sex, education, task performance or familial left-handedness.

Language dominance in neurologically normal and epilepsy subjects: a functional MRI study.

Binocular disparity provides the visual system with information concerning the three-dimensional layout of the environment. Recent physiological studies in the primary visual cortex provide a successful account of the mechanisms by which single neurons are able to signal disparity. This work also reveals that additional processing is required to make explicit the types of signal required for depth perception (such as the ability to match features correctly between the two monocular images). Some of these signals, such as those encoding relative disparity, are found in extrastriate cortex. Several other lines of evidence also suggest that the link between perception and neuronal activity is stronger in extrastriate cortex (especially MT) than in the primary visual cortex.

/pdf/the-physiology-of-stereopsis-4cewmj54vp.pdf

The physiology of stereopsis.

In patients with Alzheimer's disease (AD), compared with age-matched and young healthy control subjects, visual deficits in the following functions were observed: color, stereoacuity, contrast sensitivity, and backward masking (homogeneous and pattern). Critical flicker fusion thresholds were normal, relative to age-matched healthy subjects. For color, the majority of the errors were tritanomalous (blue axis). Color and stereoacuity deficits were unrelated to severity of dementia, in accordance with models of vision that describe these functions as modular rather than diffuse for cortical localization. Although contrast sensitivity was depressed throughout the frequency range in AD, more patients were impaired at low than at high spatial frequencies, contrasting with the observed normal aging pattern of high-frequency loss. Healthy elderly subjects showed depressed critical flicker fusion thresholds and reduced contrast sensitivity at high frequencies, relative to the young group; differences between these groups were not found for the other vision tests. A subset of the AD group received detailed neuro-ophthalmological examination, and no abnormalities were found. This finding, taken together with normal thresholds for critical flicker fusion, suggests that the widespread visual dysfunction reported here is more likely to be related to known pathological changes in primary visual and association cortex in AD than to changes in the retina or optic nerve.

Visual dysfunction in Alzheimer's disease: Relation to normal aging

Fiber density asymmetry of the arcuate fasciculus in relation to functional hemispheric language lateralization in both right- and left-handed healthy subjects: a combined fMRI and DTI study.

Table of Contents Preface Acknowledgements Contributors Section I Foundations of Neuropsychology Chapter 1- Overview of Clinical Neuropsychology Arthur MacNeill Horton, Jr and Arthur MacNeill Horton III Chapter 2-Neurological Disorders Michelle Braun Chapter 3-Neuropsychology and Intelligence: An Overview Cecil R. Reynolds, Christine L. Castillo and Arthur MacNeill Horton, Jr.

The neuropsychology handbook

The hypothesis is advanced that cerebral dominance includes two elements, interhemispheric specification for language (lateralization) and intrahemispheric language, specification (localization). Consequently, each type of aphasia is determined by the degree of dominance establishment (i.e., lateralization and localization) existing at the moment of brain damage. Evidence for this concept is presented through a comparison of aphasia in left-handers and "anomalous" dextrals with aphasia in childhood.

Lateralization and language representation.

SUMMARYThe study of Carmon and Bechtoldt reporting that a significant proportion of patients with disease of the right hemisphere show impairment in stereoscopic vision while patients with left hemisphere lesions perform on a normal level was replicated with certain modifications. The results fully confirmed the findings of the Carmon-Bechtoldt study. A majority of right-handed patients with lesions of the right hemisphere performed defectively, and all patients with left hemisphere lesions, including those with aphasia, performed on a normal level. Two left-handed patients with unilateral lesions showed a reversal of this relationship. The results are interpreted as supporting the hypothesis that the right hemisphere plays a crucial role in the realization of stereoscopic vision in man.

Stereoscopic vision in patients with unilateral cerebral disease

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Lateralization and language representation.

Stereoscopic vision in patients with unilateral cerebral disease