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Steven E Petersen

Publications and source records attributed to Steven E Petersen.

21 records · Page 2Linked to original sources

The feasibility of a common stereotactic space for children and adults in fMRI studies of development.

The question of whether pediatric and adult neuroimaging data can be analyzed in a common stereotactic space is a critical issue for developmental neuroscience. Two studies were performed to address this question. In Study 1, high-resolution structural MR brain images of 20 children (7-8 years of age) and 20 young adults (18-30 years of age) were transformed to a common space. Overall brain shape was assessed by tracing the outer boundaries of the brains in three orientations, and more local anatomy was assessed by analysis of portions of 10 selected sulci. Small, but consistent, differences in location and variability were observed in specific locations of the sulcal tracings and outer-boundary sections. In Study 2, a computer simulation was used to assess the extent to which the small anatomical differences observed in Study 1 would produce spurious effects in functional imaging data. Results indicate that, assuming a functional resolution of 5 mm in images averaged across subjects, anatomical differences in either variability or location between children and adults of the magnitude obperved in Study 1 would not negatively affect functional image comparisons. We conclude that atlas-transformed brain morphology is relatively consistent between 7- and 8-year-old children and adults at a resolution appropriate to current functional imaging and that the small anatomical differences present do not limit the usefulness of comparing child and adult functional images within a common stereotactic space.

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Reactivation of networks involved in preparatory states.

We report an endogenous signal that has a widespread cortical distribution and is time-locked to the termination of a sustained state of task-readiness. In three event-related functional magnetic resonance imaging (fMRI) experiments, subjects saw an arrow cue that predicted either the direction of motion or the location of a subsequent test stimulus. A reactivation of the BOLD (blood oxygenation level-dependent) signal occurred at the termination of the state of readiness in occipital regions that were transiently activated by the cue and in frontal-parietal regions that maintained an attentional set over the trial. Moreover, a delayed activation occurred in prefrontal and temporo-parietal regions that did not initially respond to the cue and that have been implicated in re-orienting attention to novel sensory events. These latter regions may have generated control signals that ended the state of readiness in regions active during the cue period. These results indicate that terminating a state of readiness produces a widely distributed cortical signal and suggest that areas involved in a preparatory state may be maintained as a network which can be modulated as a whole.

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Role of the posterolateral cerebellum in language.

Historically, scientists have believed that the cerebellum controls only movement. However, recent evidence from neuroimaging and human lesion studies suggests that the right posterolateral cerebellar hemisphere is involved, independently of movement, in helping an individual to generate verbs for given nouns. We sought to elucidate the key factors contributing to the verb generation deficits of subjects with right posterolateral cerebellar damage and thus to better understand the specific contributions of the postero-lateral cerebellum to language. We compared the performance of subjects with focal left-sided posterolateral cerebellar lesions, those with focal right-sided posterolateral cerebellar lesions, and neurologically normal pilot control subjects on an antonym generation task, noun (category member) generation task, verb selection task, and lexical decision task. Preliminary results show that subjects with right cerebellar lesions are impaired relative to other subjects only on the antonym generation task. The results provide evidence that the right cerebellar language deficit is not due solely to deficits in "mental movement" coupled to a verb and that internal generation of a word seems to be a key factor in eliciting a deficit. In addition, a semantic processing demand may be necessary but insufficient to elicit a right cerebellar language deficit. The results support the theory that the right posterolateral cerebellar hemisphere assists the left cerebral hemisphere in helping an individual learn to generate specific types of spoken, two-word associations. The full nature of this process awaits further investigation.

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