Biomedical subjects

E Darcy Burgund

Publications and source records attributed to E Darcy Burgund.

9 recordsLinked to original sources

PubMed2006

A core system for the implementation of task sets.

When performing tasks, humans are thought to adopt task sets that configure moment-to-moment data processing. Recently developed mixed blocked/event-related designs allow task set-related signals to be extracted in fMRI experiments, including activity related to cues that signal the beginning of a task block, "set-maintenance" activity sustained for the duration of a task block, and event-related signals for different trial types. Data were conjointly analyzed from mixed design experiments using ten different tasks and 183 subjects. Dorsal anterior cingulate cortex/medial superior frontal cortex (dACC/msFC) and bilateral anterior insula/frontal operculum (aI/fO) showed reliable start-cue and sustained activations across all or nearly all tasks. These regions also carried the most reliable error-related signals in a subset of tasks, suggesting that the regions form a "core" task-set system. Prefrontal regions commonly related to task control carried task-set signals in a smaller subset of tasks and lacked convergence across signal types.

Adolescent↗

PubMed2006

Development of letter-specific processing: the effect of reading ability.

During development, perceptual processing is tuned to inputs in the environment such that certain frequently encountered classes of stimuli are processed more effectively than similar comparison stimuli. Letters represent a class of stimuli that are encountered frequently in the environment, at least in literate cultures. Thus, the present study examined the development of letter-specific processing in children 6-19 years old by comparing the difference between performance on a letter-matching task and an unfamiliar non-letter-matching task in different subject groups. Results revealed an increase in letter-specific processing with development. Moreover, comparisons of letter-specific processing in groups of subjects matched either in age or reading ability indicate that the emergence of letter-specific processing is linked to increased reading skill, rather than increased age per se. Findings support theories of perceptual expertise, which suggest that skilled processing drives the specialization of perceptual mechanisms for certain classes of stimuli.

Adolescent↗

PubMed2005

The development of sustained and transient neural activity.

Sustained and transient signals were compared in a group of 7-8-year-old children and a group of adults performing the same cognitive task using functional magnetic resonance imaging (fMRI) in conjunction with a mixed blocked/event-related design. Results revealed several regions, including a region in the right lateral inferior frontal gyrus, that exhibited opposing developmental trajectories in sustained and transient signals--in particular, decreased sustained signals and increased transient signals with age. Re-analysis of the data assuming "blocked" and "event-related" designs, as opposed to a mixed design, produced different results. In combination, these results may help to explain contradictory findings in the literature regarding the direction of neural development in frontal cortex. Moreover, these results underscore the value of separating sustained and transient signals in fMRI studies of development.

Adolescent↗

PubMed2005

Task demands modulate sustained and transient neural activity during visual-matching tasks.

The extent to which a task demands verbal or non-verbal processing may influence which neural regions underlie performance. In the present study, sustained and transient responses were examined using functional magnetic resonance imaging (fMRI) in conjunction with a mixed blocked/event-related design during three visual-matching tasks that varied in the extent to which they relied on verbal processing. In a name-matching task, subjects decided whether two letters had the same or a different name (e.g., A a); in a physical-matching task, subjects decided whether two letters were exactly the same or different (e.g., A A); in a non-letter-matching task, subjects decided whether two non-letters were exactly the same or different. Results revealed several regions in which sustained activity differed across the three tasks as well as several regions in which sustained activity did not differ. Most notably, regions in the right inferior frontal gyrus exhibited greater sustained activity during the name-matching task than during the physical or non-letter-matching tasks, indicating that sustained activity in this region is sensitive to the amount of verbal processing required by a particular task. Moreover, transient activity in the right inferior frontal regions, as well as others, exhibited the opposite pattern of results. In combination, results suggest that sustained and transient activities interact to produce the context-appropriate response during visual-matching tasks.

Adolescent↗

PubMed2005

Initial storage of unfamiliar objects: examining memory stores with signal detection analyses.

The memory source(s) underlying performance of the object decision task were examined. Application of signal detection theory with independent indices of sensitivity and bias indicated that greater object decision sensitivity (possible vs. impossible object discrimination) is observed for primed than for unprimed objects and a greater bias to respond "possible" is observed for primed than for unprimed objects. To test whether a single memory store underlies the two effects, we assessed whether the two effects would be influenced in similar ways by a particular experimental manipulation. Sensitivity did not differ between processing of 180 degrees -rotated primed objects vs. un-rotated primed objects, but bias to respond "possible" differed between those conditions in predictable ways depending on the cerebral hemisphere of direct test presentations. Results support a conciliatory resolution to the debate concerning memory in this task and help to clarify properties of memory stores underlying the initial storage of unfamiliar objects.

Adult↗

PubMed2003

Comparison of functional activation foci in children and adults using a common stereotactic space.

The development of methods allowing direct comparisons between child and adult neuroimaging data is an important prerequisite for studying the neural bases of cognitive development. Several issues arise when attempting to make such direct comparisons, including the comparability of anatomical localization of functional responses and the magnitude and time course of the hemodynamic responses themselves. Previous results suggest that, after transformation into a common stereotactic space, anatomical differences between children (ages 7 and 8) and adults are small relative to the resolution of fMRI data. Here, we investigate whether time courses (BOLD responses) and locations of functional activation foci show similarities as well. Event-related fMRI was performed on 16 children (ages 7 and 8) and 16 adults, who pressed buttons in response to a visual stimulus. After transforming images into Talairach space, the coordinates of four consistent activations in each hemisphere were determined for each subject: two foci in the sensorimotor cortex, one focus in the visual cortex, and one focus in the supplementary motor area (eight activations in total). In seven foci, time courses were similar between children and adults, and peak amplitudes of time courses were comparable in all eight foci. There were negligible between-group differences in location of all foci. Variability of activation location was statistically similar in the two groups. In voxelwise group comparison images, minimal differences were found between children and adults in visual and motor cortex regions. The small differences in time courses and locations of activation foci between child and adult brains validate the feasibility of direct statistical comparison of these groups within a common space.

Adult↗

PubMed2003

Sustained and transient activity during an object-naming task: a mixed blocked and event-related fMRI study.

Cognitive tasks often involve at least two types of processes-sustained processes potentially related to ongoing task demands and transient processes related to the processing of individual items within the task. Using functional magnetic resonance imaging, in conjunction with a mixed-blocked and event-related design, we examined sustained and transient patterns of neural activity during an object-naming task. Subjects were imaged during runs that alternated between control blocks and task blocks. During task blocks, primed and unprimed objects were intermixed and jittered in time. Regions of interest based on separate analyses of sustained and transient activities were tested independently for sustained and transient responses. Three general patterns of results were observed. (1) Some regions exhibited transient responses but little or no sustained response. These regions were widely distributed across the brain. (2) Other regions clearly exhibited both transient and sustained responses. These regions were found primarily in lateral and medial frontal lobes. (3) A few regions exhibited a sustained response but little or no transient responses. These regions were found in the basal ganglia, orbitofrontal lobe, and right lateral frontal lobe. Furthermore, two homotopic regional pairs in the right and left inferior frontal lobe (frontal operculum and inferior frontal cortex) showed a crossover of sustained and transient effects, with greater transient activity in the left and greater sustained activity in the right hemisphere. The asymmetric relationship between sustained and transient responses in prefrontal regions may be an example of task-specific biasing at work.

Adult↗

PubMed2003

Serotonin levels influence patterns of repetition priming.

Repetition priming in a word-stem completion task was examined in a group of control subjects and in a group of experimental subjects under conditions of acute tryptophan depletion (T-) and tryptophan augmentation (T+). Experimental subjects ingested amino acid compounds that depleted or loaded the body with tryptophan, and word-stem completion priming performance was measured. Results indicate differential effects of T- and T+ manipulations on word-stem completion priming. In the control group, both specific-visual and amodal priming were observed. Conversely, in the T+ condition, specific-visual priming, but no amodal priming, was observed, whereas in the T- condition, amodal priming, but no specific-visual priming, was observed. The authors conclude that serotonin (5-hydroxytryptamine) plays a critical role in repetition priming by helping to modulate which neural systems contribute to priming effects.

Adolescent↗

PubMed2002

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.

Adolescent↗