Showing papers by "Russell A. Poldrack published in 2000"

Disruption of the neural response to rapid acoustic stimuli in dyslexia: Evidence from functional MRI

Abstract: The biological basis for developmental dyslexia remains unknown. Research has suggested that a fundamental deficit in dyslexia is the inability to process sensory input that enters the nervous system rapidly and that deficits in processing rapid acoustic information are associated with impaired reading. Functional magnetic resonance imaging (fMRI) was used to identify the brain basis of rapid acoustic processing in normal readers and to discover the status of that response in dyslexic readers. Normal readers showed left prefrontal activity in response to rapidly changing, relative to slowly changing, nonlinguistic acoustic stimuli. Dyslexic readers showed no differential left frontal response. Two dyslexic readers participated in a remediation program and showed increased activity in left prefrontal cortex after training. These fMRI results identify left prefrontal regions as normally being sensitive to rapid relative to slow acoustic stimulation, insensitive to the difference between such stimuli in dyslexic readers, and plastic enough in adulthood to develop such differential sensitivity after intensive training.

Neural Activation During Response Competition

Abstract: The flanker task, introduced by Eriksen and Eriksen lEriksen, B. A., & Eriksen, C. W. (1974). Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics, 16, 143–149r, provides a means to selectively manipulate the presence or absence of response competition while keeping other task demands constant. We measured brain activity using functional magnetic resonance imaging (fMRI) during performance of the flanker task. In accordance with previous behavioral studies, trials in which the flanking stimuli indicated a different response than the central stimulus were performed significantly more slowly than trials in which all the stimuli indicated the same response. This reaction time effect was accompanied by increases in activity in four regions: the right ventrolateral prefrontal cortex, the supplementary motor area, the left superior parietal lobe, and the left anterior parietal cortex. The increases were not due to changes in stimulus complexity or the need to overcome previously learned associations between stimuli and responses. Correspondences between this study and other experiments manipulating response interference suggest that the frontal foci may be related to response inhibition processes whereas the posterior foci may be related to the activation of representations of the inappropriate responses.

Neural activity differs between explicit and implicit learning of artificial grammar strings: An fMRI study

Abstract: Functional magnetic resonance imaging was used to investigate the neural areas underlying retrieval of implicit and explicit knowledge about letter strings. Participants studied strings formed according to an artificial grammar, then performed implicit-learning-based judgments (judging the grammatical status of the string) or explicit-learning-based judgments (recognition) on novel grammatical strings. In comparison with a baseline task, recognition and grammatical judgments led to different patterns of neural activation: Recognition activated the right frontal cortex, whereas grammatical judgment activated the left frontal cortex. Recognition led to higher activity in the precuneus and medial occipital cortex, whereas grammatical judgments led to suppression of activity in the precuneus and activation in the lateral occipital cortex. When the surface structure of the strings was changed, grammatical judgments led to bilateral frontal activity and bilateral but left-lateralized activity in the occipital and parietal lobes. These results provide further evidence for a dissociation between the neural bases of implicit and explicit learning.

Analysis of cerebral white matter for prognosis and diagnosis of neurological disorders

Abstract: A method of detecting a neurological disorder such as dyslexia includes the steps of measuring microstructure of cerebral white matter, and correlating the microstructure to the presence of the neurological disorder. For dyslexia, the white matter is confined to temporo-parietal white matter. The microstructure is measured by determining cerebral white matter anisotropy using diffusion tensor magnetic resonance imaging (DTI).