Biomedical subjects

Graeme Jackson

Publications and source records attributed to Graeme Jackson.

5 recordsLinked to original sources

PubMed2003

Head position modulates activity in the human parietal eye fields.

For us to interact with our environment we need to know where objects are around us, relative to our body. In monkeys, a body-centered map of visual space is known to exist within the parietal eye fields. This map is formed by the modulation of retinal responses by gain fields to gaze position. In humans, no map of body-centered space has yet been discovered but clinical data suggest that the right parietal lobe is predominantly responsible for visuospatial function. Using functional MRI, we have been able to demonstrate that an area in the intraparietal sulcus of humans has properties very similar to the parietal eye fields of monkeys. This area demonstrates BOLD signal changes related to the visual, saccadic, and memory components of saccade tasks that are analogous to the visual, saccadic, and memory responses of neurons within the parietal eye fields of monkeys. More importantly, the amount of signal change seen in this region is modulated by head position relative to the body, suggesting that a gain field dependent body-centered representation of space exists bilaterally within the parietal lobes in humans.

Adult↗

PubMed2003

Evaluating subject specific preprocessing choices in multisubject fMRI data sets using data-driven performance metrics.

This study investigated the possible benefit of subject specific optimization of preprocessing strategies in functional magnetic resonance imaging (fMRI) experiments. The optimization was performed using the data-driven performance metrics developed recently [Neuroimage 15 (2002), 747]. We applied numerous preprocessing strategies and a multivariate statistical analysis to each of the 20 subjects in our two example fMRI data sets. We found that the optimal preprocessing strategy varied, in general, from subject to subject. For example, in one data set, optimum smoothing levels varied from 16 mm (4 subjects), 10 mm (5 subjects), to no smoothing at all (1 subject). This strongly suggests that group-specific preprocessing schemes may not give optimum results. For both studies, optimizing the preprocessing for each subject resulted in an increased number of suprathresholded voxels in within-subject analyses. Furthermore, we demonstrated that we were able to aggregate the optimized data with a random effects group analysis, resulting in improved sensitivity in one study and the detection of interesting, previously undetected results in the other.

Adult↗

PubMed2002

Quality assurance and radiofrequency heating.

This paper proposes an inexpensive means of assessing radiofrequency (RF) power deposition in a magnet. This is particularly important at 3T where sequences approach Food and Drug Administration approved RF limits. It will also be of interest to operators at 1.5 T as part of their ongoing quality assurance programs. At 3T, we found that the RF power deposited in the magnet was less than that read by the MR power monitor.

Electromagnetic Phenomena↗

PubMed2002

Mixed lateralization of phonological assembly in developmental dyslexia.

Developmental phonological dyslexia has been characterized as a deficit in phonological assembly. At a neural level, it is possible that this deficit is represented by weak connectivity between anterior and posterior language systems in the left hemisphere. This study used 3-Tesla functional magnetic resonance imaging to investigate phonological assembly in a developmental phonological dyslexic. The phonological dyslexic showed increased activation in the left hemisphere of the inferior frontal gyrus (BA 44/6) and increased activation in the right hemisphere of the parietal cortex (BA 7), occipital cortex (BA 18), and in the cerebellum, as phonological demands were systematically increased. Converging evidence suggests that the core dysfunction in phonological dyslexia resides in and around the angular gyrus of the left hemisphere. This study supports the compensatory role of posterior regions in the right hemisphere together with the left inferior frontal gyrus.

Adult↗

PubMed2002

Differential functional magnetic resonance imaging language activation in twins discordant for a left frontal tumor.

Eight-year-old twins, one with a left frontal tumor and aphasic seizures, the other neurologically normal, underwent serial assessment of expressive language with functional magnetic resonance imaging and neuropsychology. The affected twin showed a significant amount of right hemisphere activation coincident with behavioral deterioration in expressive language and late growth in the tumor. This pattern of language dysfunction and the left language dominance of her co-twin suggested that the affected twin was also left dominant for language, and the significance of her right activation is discussed. We postulate that the right hemisphere activation represents a stabilizing mechanism in the context of a developmental and progressive lesion in language cortex rather than language transfer per se.

Brain Neoplasms↗