Biomedical subjects

Kristina M Visscher

Publications and source records attributed to Kristina M Visscher.

4 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↗

PubMed2004

Comparison of sustained and transient activity in children and adults using a mixed blocked/event-related fMRI design.

The ability to make direct comparisons between adult and child neuroimaging data is important to the study of the neural basis of cognitive development. Recent fMRI studies in adults have used mixed blocked/event-related designs to extract activity consistent with separable sustained, task-related processes and transient, trial-related processes. Because brain regions with different time courses of activity may have different roles in cognitive processing, the ability to distinguish between sustained and transient signals would contribute to understanding the functional roles of regions involved in cognitive processing. The developmental profile of such activity would give insight into how cognitive processing develops over time. The purpose of this study was to assess the utility of the mixed design to detect and dissociate sustained and transient activity in children, and to determine if the time courses or magnitudes of the extracted signals differ from those extracted from adults. An fMRI experiment was performed on 10 adults and 10 children (ages 7-8) using counterphase flickering checkerboard stimuli that produced sustained, transient, and a combination of sustained and transient responses in visual cortex. Analyses were performed using the general linear model (GLM) assuming a shape for sustained effects, but not for transient effects. In visual cortex, neither transient nor sustained effects showed significant between-group differences. For both groups, flickering checkerboard stimuli produced robust responses in visual cortex contralateral but not ipsilateral to the stimulus. Results extend the feasibility of direct statistical comparison of adults and children; mixed designs provide a means to examine neural activity in both adults and children related to sustained, task-level processes, likely related to task-level control.

Adult↗

PubMed2003

Mixed blocked/event-related designs separate transient and sustained activity in fMRI.

Recent functional magnetic resonance imaging (fMRI) studies using mixed blocked/event-related designs have shown activity consistent with separable sustained task-related processes and transient trial-related processes. In the mixed design, control blocks are intermixed with task blocks, during which trials are presented at varying intervals. Two studies were conducted to assess the ability of this design to detect and dissociate sustained task-related from transient trial-related activity. Analyses on both simulated and empirical data were performed by using the general linear model with a shape assumed for sustained effects, but not transient effects. In the first study, simulated data were produced with sustained time courses, transient time courses, and the sum of both together. Analyses of these data showed appropriate parsing of sustained and transient activity in all three cases. For the empirical fMRI experiment, counterphase-flickering checkerboard stimuli were constructed to produce sustained, transient, and combined sustained and transient responses in visual cortex. As with the simulation, appropriate parsing of sustained and transient activity was seen in all three cases; i.e., sustained stimuli produced sustained time courses and transient stimuli produced transient time courses. Combined stimuli produced both transient and sustained time courses. Critically, transient stimuli alone did not produce spurious positive sustained responses; sustained stimuli alone produced negligible spurious transient time courses. The results of these two studies along with supplemental simulations provide strong evidence that mixed designs are an effective tool for separating transient, trial-related activity from sustained activity in fMRI experiments. Mixed designs can allow researchers a means to examine brain activity associated with sustained processes, potentially related to task-level control signals.

Attention↗

PubMed2002

Functional neuroanatomical differences between adults and school-age children in the processing of single words.

A critical issue in developmental cognitive neuroscience is the extent to which the functional neuroanatomy underlying task performance differs in adults and children. Direct comparisons of brain activation in the left frontal and extrastriate cortex were made in adults and children (aged 7 to 10 years) performing single-word processing tasks with visual presentation; differences were found in circumscribed frontal and extrastriate regions. Conceivably, these differences could be attributable exclusively to performance discrepancies; alternatively, maturational differences in functional neuroanatomy could exist despite similar performance. Some of the brain regions examined showed differences attributable to age independent of performance, suggesting that maturation of the pattern of regional activations for these tasks is incomplete at age 10.

Adolescent↗