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Steven E Petersen

Publications and source records attributed to Steven E Petersen.

At least 19 recordsLinked to original sources
PubMed2006

fMRI reveals novel functional neuroanatomy in a child with perinatal stroke.

Children who have experienced a perinatal stroke often develop normal language function, but the neurobiologic mechanisms underlying this plasticity remain unclear. In this study, we used fMRI to compare, at two ages, the functional neuroanatomy of a child with perinatal stroke with that of age-appropriate cohorts of typically developing children. Although the data for this child are similar to the control group, there are age-dependent differences.

Adolescent↗
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↗
PubMed2006

A comparison of analysis of variance and correlation methods for investigating cognitive development with functional magnetic resonance imaging.

Statistical approaches used in functional magnetic resonance imaging (fMRI) to study cognitive development are varied and evolving. Two approaches have generally been used. These are between-group end-point analysis of variance (ANOVA) and age-related regression. Differences in these 2 approaches could produce different results when applied to a single data set. Event-related fMRI data from a group of typically developing participants (n = 95; age range = 7-35 years) performing controlled lexical processing tasks were analyzed using both methods. Results from the 2 approaches showed significant overlap, but also noteworthy differences. The results suggest that for regions showing age-related changes, correlation was relatively more sensitive to more linear changes whereas ANOVA was relatively more sensitive to less-linear changes. These findings suggest that full characterization of developmental dynamics will require converging methodologies.

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

Intermanual transfer effects in sequential tactuomotor learning: evidence for effector independent coding.

Results from our earlier brain imaging studies regarding motor learning have shown different areas activated during naive and practiced performance. When right handed participants moved a pen either with the dominant or non-dominant hand continuously through a cut-out maze as quickly and accurately as possible, practice resulted in decreased brain activity in right premotor and parietal areas as well as left cerebellum, while increased activity was found in the supplementary motor area (SMA). These lateralized practiced-related changes in brain activation suggest effector-independent abstract coding of information. To test this hypothesis more extensively, intermanual transfer of learning was examined in 24 male and female participants (12 right- and 12 left-handed) using the same maze-learning task. It was hypothesized that if an abstract representation of the movement is learned and stored, intermanual transfer effects should be more pronounced when participants transferred to a same maze as opposed to a mirror image of the maze. Errors and velocity were measured during the following conditions: initial naive performance (Naive); after practice on the maze (Prac); during intermanual transfer to the same maze (Transfer Identical); and to the mirror maze (Transfer Mirror). Transfer direction was tested from the dominant to non-dominant hand and vice versa. No significant differences were found between right- and left-handed participants, males and females, and transfer directions. However, intermanual transfer of learning was significantly greater to the identical maze as opposed to the mirror maze. These results showed that learning was indeed taking place at an abstract effector independent level.

Adolescent↗
PubMed2005

Evidence for separate perceptual reactivation and search processes during remembering.

Remembering involves the coordinated recruitment of strategic search processes and processes involved in reconstructing the content of the past experience. In the present study we used a cueing paradigm based on event-related functional magnetic resonance imaging to separate activity in the initial preparation phases of retrieval from later phases during which retrieval search ensued, and detailed auditory and visual memories were reconstructed. Results suggest a dissociation among inferior temporal (IT) and parieto-occipital (PO) processing regions in how they were influenced by preparatory cues prior to remembering, and indicate a dissociation in how they were influenced by the subsequent validity of those cues during remembering. Regions in IT cortex appeared to show search-related activity during retrieval, as well as robust modality effects, but they were not influenced by preparatory cues. These findings suggest a specific role for IT regions in reconstruction of visual details during remembering. While dorsal regions in parietal and superior occipital cortex also appeared to show search-related activity as well as robust modality effects, they were also influenced by preparatory cues during the retrieval phase, and to a lesser degree during the cue phase. These findings indicate a role in integrating perceptual reactivation and search processes during remembering.

Adaptation, Physiological↗
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↗
PubMed2004

Developmental changes in human cerebral functional organization for word generation.

A fundamental issue in cognitive neuroscience is the nature of developmental changes in human cerebral functional organization for higher cognitive functions. Event-related functional magnetic resonance imaging was used to measure developmental changes in the functional neuroanatomy subserving controlled lexical association. First, brain regions showing significant differences in activity between school-age children and young adults, despite equivalent task performance, were identified. Then, activity in these regions was more fully characterized in individuals spanning the ages of 7-32 years old. Cross-sectional and regression analyses showed systematic increases and decreases in levels of activity over age, by region. Age-related increases in activity were primarily newly recruited, later-stage processing regions, such as in left frontal and left parietal cortex. Decreases, on the other hand, were all positive activations that attenuated with age and were found across a wider neuroanatomical range, including earlier processing regions such as bilateral extrastriate cortex. The hemodynamic magnitude, neuroanatomical location and maturational timecourse of these progressive and regressive changes have implications for models of the developing specialization in human cerebral functional organization.

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↗
PubMed2004

Functional changes in brain activity during acquisition and practice of movement sequences.

In the present study, brain activations were measured using positron emission tomography (PET) over the course of practice. Fourteen right-handed participants were scanned during six 1-min periods of practice tracing a cut-out maze design with their eyes closed. Practice-related decreases were found in the right premotor and posterior parietal cortex and left cerebellum, increases in the supplementary motor area (SMA) and primary motor cortex. The decrease in right premotor activity and the increase in SMA was significantly correlated with a decrease in the number of stops, implying involvement in learning and storing the movement sequence. The significant correlation between decreases in errors and left cerebellar and right posterior parietal activity suggests a role in accuracy. Involvement of the primary motor cortex in motor execution is suggested by the correlation of increased activation and movement speed. These results suggest that different neural structures (involving a premotor-parietal-cerebellar circuit) play a role in a sequential maze learning task.

Adult↗
PubMed2003

A procedure for identifying regions preferentially activated by attention to semantic and phonological relations using functional magnetic resonance imaging.

A procedure is introduced for using functional magnetic resonance imaging (fMRI) techniques to identify neural regions associated with attention to semantic and phonological aspects of written words within a single group of subjects. Short lists (16 words/list), consisting of visually-presented semantically-related words (bed, rest) or rhyming words (weep, beep) were presented rapidly to subjects, who were asked to attend to the relations among the words. Regions preferentially involved in attention to semantic relations appeared within left anterior/ventral inferior frontal gyrus (IFG, approximate Brodmann Area, BA47), left posterior/dorsal IFG (BA44/45), left superior/middle temporal cortex (BA22/21), left fusiform gyrus (BA37), and right cerebellum. Regions preferentially involved in attention to phonological relations appeared within left inferior frontal cortex (near BA6/44, posterior to the semantic regions within IFG described above) and within bilateral inferior parietal cortex (BA40) and precuneus (BA7). This method is notable in that a comparison of the two tasks within some of the individual subjects revealed activation patterns similar to the group average, especially within left inferior frontal and left superior/middle parietal cortices. This fact combined with the efficiency with which the data can be obtained (here, in about an hour of functional scanning) and the adaptability of the task for many different subject populations suggests a wide range of possibilities for this technique: it could be used to track language development (e.g. in children), compare language organization across subject populations (e.g. for dyslexic or blind subjects), and identify language regions within individuals (e.g. potentially to aid in surgical planning).

Adolescent↗
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

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

Word retrieval learning modulates right frontal cortex in patients with left frontal damage.

Previous studies have suggested that recovery or compensation of language function after a lesion in the left hemisphere may depend on mechanisms in the right hemisphere. However, a direct relationship between performance and right hemisphere activity has not been established. Here, we show that patients with left frontal lesions and partially recovered aphasia learn, at a normal rate, a novel word retrieval task that requires the damaged cortex. Verbal learning is accompanied by specific response decrements in right frontal and right occipital cortex, strongly supporting the compensatory role of the right hemisphere. Furthermore, responses in left occipital cortex are abnormal and not modulated by practice. These findings indicate that frontal cortex is a source of top-down signals during learning.

Aphasia, Broca↗
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↗