Arrow Research search

Author name cluster

Douglas C. Noll

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

22 papers
1 author row

Possible papers

22

YNIMG Journal 2006 Journal Article

Vascular dynamics and BOLD fMRI: CBF level effects and analysis considerations

  • Alberto L. Vazquez
  • Eric R. Cohen
  • Vikas Gulani
  • Luis Hernandez-Garcia
  • Ying Zheng
  • Gregory R. Lee
  • Seong-Gi Kim
  • James B. Grotberg

Changes in the cerebral blood flow (CBF) baseline produce significant changes to the hemodynamic response. This work shows that increases in the baseline blood flow level produce blood oxygenation-level dependent (BOLD) and blood flow responses that are slower and lower in amplitude, while decreases in the baseline blood flow level produce faster and higher amplitude hemodynamic responses. This effect was characterized using a vascular model of the hemodynamic response that separated arterial blood flow response from the venous blood volume response and linked the input stimulus to the vascular response. The model predicted the baseline blood flow level effects to be dominated by changes in the arterial vasculature. Specifically, it predicted changes in the arterial blood flow time constant and venous blood volume time constant parameters of +294% and −24%, respectively, for a 27% increase in the baseline blood flow. The vascular model performance was compared to an empirical model of the hemodynamic response. The vascular and empirical hemodynamic models captured most of the baseline blood flow level effects observed and can be used to correct for these effects in fMRI data. While the empirical hemodynamic model is easy to implement, it did not incorporate any explicit physiological information.

Details DOI

YNIMG Journal 2005 Journal Article

Accounting for nonlinear BOLD effects in fMRI: parameter estimates and a model for prediction in rapid event-related studies

  • Tor D. Wager
  • Alberto Vazquez
  • Luis Hernandez
  • Douglas C. Noll

Nonlinear effects in fMRI BOLD data may substantially influence estimates of task-related activations, particularly in rapid event-related designs. If the BOLD response to each stimulus is assumed to be independent of the stimulation history, nonlinear interactions create a prediction error that may reduce sensitivity. When stimulus density differs among conditions, nonlinear effects can cause artifactual differences in activation. This situation can occur in rapid event-related designs or when comparing blocks of unequal lengths. We present data showing substantial nonlinear history effects for stimuli 1 s apart and use estimates of nonlinearities in response magnitude, onset time, and time to peak to form a low-dimensional parameterization of these nonlinear effects. Our estimates of nonlinearity appear relatively consistent throughout the brain, and these estimates can be used to form adjusted linear predictors for future rapid event-related fMRI studies. Adjusting the linear model for these known nonlinear effects results in a substantially better model fit. The biggest advantages to using predictors adjusted for known nonlinear effects are (1) higher sensitivity at the individual subject level of analysis, (2) better control of confounds related to nonlinear effects, and (3) more accurate estimates of design efficiency in experimental fMRI design.

Details DOI

YNIMG Journal 2000 Journal Article

Working Memory for Letters, Shapes, and Locations: fMRI Evidence against Stimulus-Based Regional Organization in Human Prefrontal Cortex

  • Leigh E. Nystrom
  • Todd S. Braver
  • Fred W. Sabb
  • Mauricio R. Delgado
  • Douglas C. Noll
  • Jonathan D. Cohen

Investigations of working memory (WM) systems in the frontal cortex have revealed two stimulus dimensions along which frontal cortical representations may be functionally organized. One hypothesized dimension dissociates verbal from nonverbal WM processes, dividing left from right frontal regions. The second hypothesized dimension dissociates spatial from nonspatial WM, dividing dorsal from ventral frontal regions. Here we used functional magnetic resonance imaging to probe WM processes associated with three different types of stimuli: letters (verbal and nonspatial), abstract shapes (nonverbal and nonspatial), and locations (nonverbal and spatial). In a series of three experiments using the “n-back” WM paradigm, direct statistical comparisons were made between activation patterns in each pairwise combination of the three stimulus types. Across the experiments, no regions that demonstrated responses to WM manipulations were discovered to be unique to any of the three stimulus types. Therefore, no evidence was found to support either a left/right verbal/nonverbal dissociation or a dorsal/ventral spatial/nonspatial dissociation. While this could reflect a limitation of the present behavioral and imaging techniques, other factors that could account for the data are considered, including subjects' strategy selection, encoding of information into WM, and the nature of representational schemes in prefrontal cortex.

Details DOI

YNIMG Journal 1999 Journal Article

A Developmental Functional MRI Study of Spatial Working Memory

  • Kathleen M. Thomas
  • Steven W. King
  • Peter L. Franzen
  • Tomihisa F. Welsh
  • Aaron L. Berkowitz
  • Douglas C. Noll
  • Vered Birmaher
  • B.J. Casey

Functional magnetic resonance imaging (fMRI) was used to examine patterns of cortical activity in children during performance of a spatial working memory task. Six children (8–10 years) and six adults (19–26 years) searched a linear array of four boxes for the appearance of a dot. In the visual blocks, participants made no response. In the motor blocks, participants were instructed to indicate the location of the dot on each trial using a button-press response. In the working memory blocks, participants were instructed to indicate at which location the dot had appeared 1 or 2 trials previously. Both children and adults showed activity in the left precentral and postcentral gyri, as well as the right cerebellum for the motor condition as compared to the visual condition. Comparison of the memory and motor conditions revealed reliable activity in the right superior frontal gyrus (BA 8), right dorsolateral prefrontal cortex (BA 10/46), right superior parietal cortex, and bilateral inferior parietal cortex for both adults and children. These results suggest that spatial working memory tasks activate very similar cortical regions for school-age children and adults. The findings differ from previous imaging studies of nonspatial working memory tasks in that the prefrontal activations observed in the current work tend to be more dorsal. Results are discussed in light of the significant behavioral performance differences observed between child and adult participants.

Details DOI

YNIMG Journal 1999 Journal Article

A Direct Comparison between Whole-Brain PET and BOLD fMRI Measurements of Single-Subject Activation Response

  • Paul E. Kinahan
  • Douglas C. Noll

We present the results of a direct comparison of single-subject activation using identical tasks for both functional PET and fMRI whole-brain studies. We examined the most commonly employed methods for each modality. For fMRI this is the blood oxygenation level-dependent (BOLD) contrast method with echo-planar imaging. In PET single-subject activation studies are based on the development of high sensitivity 3D imaging of regional cerebral blood flow from multiple [15O]water injections. The identical activation paradigm of a visually cued sequential finger opposition was used for PET and fMRI. For both modalities the entire brain volume difference images were smoothed to the same final resolution and the peaktvalue within the primary sensory/motor (PSM) area was then identified. All contiguous voxels in the PSM above a predetermined threshold of statistical significance were determined. Finally, the difference-weighted centroid location was calculated for the PSM region for each modality. These studies showed a very similar pattern of activation, with the volume of activation greater in fMRI and higher levels of statistical significance. The centroids of activation, however, differed by 9 ± 3 mm between the modalities, with the fMRI centroid location dorsal to that for PET. These results were stable across all processing options including differing levels of image smoothing and thresholds of statistical significance. These results are consistent with the hypothesis that draining veins contribute a substantial signal for fMRI activation studies and indicate caution for the interpretation of BOLD fMRI images with activation sites near draining veins.

Details DOI

YNIMG Journal 1999 Journal Article

Overt Verbal Responding during fMRI Scanning: Empirical Investigations of Problems and Potential Solutions

  • Deanna M. Barch
  • Fred W. Sabb
  • Cameron S. Carter
  • Todd S. Braver
  • Douglas C. Noll
  • Jonathan D. Cohen

This paper presents a pair of studies designed to empirically explore the severity of potential artifacts associated with overt verbal responding during fMRI scanning and to examine several different solutions to these artifacts. In Study One, we compared susceptibility artifacts, signal-to-noise ratios, and activation patterns when overt versus covert verbal responses were elicited during fMRI scanning, using both individual and group analyses. The results indicated that different patterns of brain activation were elicited during covert as compared to overt verbal responses. This suggests that covert responses cannot be used as a simple substitute for overt verbal responses. Further, the results suggested that the use of overt verbal responses during fMRI scanning can produce interpretable results if: (1) the primary comparison is between two conditions that both use overt verbal responses, and (2) analyses are conducted on pooled group data rather than individual participant data. In Study Two, we evaluated the feasibility and validity of a method for acquiring participants' overt responses during fMRI scanning. The results indicated that our method was very accurate in acquiring the content of participant's responses. Further, inspection of the responses demonstrated that participants do not always comply with task instructions and highlighted the importance of obtaining behavioral performance measures during fMRI scanning.

Details DOI

YNIMG Journal 1998 Journal Article

Nonlinear Aspects of the BOLD Response in Functional MRI

  • Alberto L. Vazquez
  • Douglas C. Noll

Functional magnetic resonance imaging (fMRI) using blood oxygenation level-dependent (BOLD) contrast has progressed rapidly and is commonly used to study function in many regions of the human brain. This paper introduces a method for characterizing the linear or nonlinear properties of the hemodynamic response. Such characterization is essential for accurate prediction of time-course behavior. Linearity of the BOLD response was examined in the primary visual cortex for manipulations of the stimulus amplitude and duration. Stimuli of 1, 2, 4, and 8 s duration (80% contrast) and 10, 20, 40, and 80% contrast (4 s duration) were used to test the hemodynamic response. Superposition of the obtained responses was performed to determine if the BOLD response is nonlinear. The nonlinear characteristics of the BOLD response were assessed using a Laplacian linear system model cascaded with a broadening function. Discrepancies between the model and the observed response provide an indirect measure of the nonlinearity of the response. The Laplacian linear system remained constant within subjects so the broadening function can be used to absorb nonlinearities in the response. The results show that visual stimulation under 4 s in duration and less than 40% contrast yield strong nonlinear responses.

Details DOI

YNIMG Journal 1998 Journal Article

Reproducibility of fMRI Results across Four Institutions Using a Spatial Working Memory Task

  • B.J. Casey
  • Jonathan D. Cohen
  • Kathy O'Craven
  • Richard J. Davidson
  • William Irwin
  • Charles A. Nelson
  • Douglas C. Noll
  • Xiaoping Hu

Four U. S. sites formed a consortium to conduct a multisite study of fMRI methods. The primary purpose of this consortium was to examine the reliability and reproducibility of fMRI results. FMRI data were collected on healthy adults during performance of a spatial working memory task at four different institutions. Two sets of data from each institution were made available. First, data from two subjects were made available from each site and were processed and analyzed as a pooled data set. Second, statistical maps from five to eight subjects per site were made available. These images were aligned in stereotactic space and common regions of activation were examined to address the reproducibility of fMRI results when both image acquisition and analysis vary as a function of site. Our grouped and individual data analyses showed reliable patterns of activation in dorsolateral prefrontal cortex and posterior parietal cortex during performance of the working memory task across all four sites. This multisite study, the first of its kind using fMRI data, demonstrates highly consistent findings across sites.

Details DOI

YNIMG Journal 1998 Journal Article

Suppression of Vascular Artifacts in Functional Magnetic Resonance Images Using MR Angiograms

  • Petr Hluštı́k
  • Douglas C. Noll
  • Steven L. Small

This paper describes a method for processing functional magnetic resonance images that suppresses signal changes originating from macroscopic veins visible in acquired magnetic resonance angiograms. Finger tapping experiments were performed on a 1. 5-T scanner and the response was evaluated with voxel-by-voxel cross-correlation of the time course with a sinusoid at the paradigm frequency. After applying a vascular mask to suppress signal changes under macroscopic vessels, the vascular and nonvascular subpopulations of the data were compared. By visual inspection, the method was found to remove extracortical activation while preserving activation in the parenchyma. The observed higher signal amplitudes and temporal phase lags of the vascular population agree with theoretical models and previous studies. A significant portion of negatively correlated voxels occurs adjacent to through-plane vessels. Finally, comparing the centers of mass of the activated area before and after vascular suppression showed significant shifts in some subjects.

Details DOI

YNIMG Journal 1997 Journal Article

A Parametric Study of Prefrontal Cortex Involvement in Human Working Memory

  • Todd S. Braver
  • Jonathan D. Cohen
  • Leigh E. Nystrom
  • John Jonides
  • Edward E. Smith
  • Douglas C. Noll

Although recent neuroimaging studies suggest that prefrontal cortex (PFC) is involved in working memory (WM), the relationship between PFC activity and memory load has not yet been well-described in humans. Here we use functional magnetic resonance imaging (fMRI) to probe PFC activity during a sequential letter task in which memory load was varied in an incremental fashion. In all nine subjects studied, dorsolateral and left inferior regions of PFC were identified that exhibited a linear relationship between activity and WM load. Furthermore, these same regions were independently identified through direct correlations of the fMRI signal with a behavioral measure that indexes WM function during task performance. A second experiment, using whole-brain imaging techniques, both replicated these findings and identified additional brain regions showing a linear relationship with load, suggesting a distributed circuit that participates with PFC in subserving WM. Taken together, these results provide a “dose–response curve” describing the involvement of both PFC and related brain regions in WM function, and highlight the benefits of using graded, parametric designs in neuroimaging research.

Details DOI

YNIMG Journal 1995 Journal Article

Activation of Prefrontal Cortex in Children during a Nonspatial Working Memory Task with Functional MRI

  • B.J. Casey
  • Jonathan D. Cohen
  • Peter Jezzard
  • Robert Turner
  • Douglas C. Noll
  • Rolf J. Trainor
  • Jay Giedd
  • Debra Kaysen

Functional magnetic resonance imaging (fMR1) was used to examine the pattern of activity of prefrontal cortex in prepubertal children during performance of a nonspatial working memory task. The children observed sequences of letters and responded whenever a letter repeated with exactly one nonidentical letter intervening. In a comparison task, subjects monitored similar sequences of letters for any occurrence of a single, prespecified target letter. Location of activation closely approximated that observed in a recent fMRI study with adults using exactly the same task. Activation of the inferior and middle frontal gyri was reliably observed within individual subjects during performance of the working memory task relative to the comparison task. Activation increased and decreased with a time course that was highly consistent with the task manipulations and correlated with behavioral performance. To our knowledge, this study is one of the first to demonstrate the applicability of fMRI to a normative developmental population. Issues of age dependence of the hemodynamic responses of fMRI are discussed.

Details DOI
v2026.09.13