Is There a Different Type of MR-Contrast in the Early Phase of Functional Activation?

Hennig, Juergen; Janz, C.; Speck, Oliver; Ernst, Thomas

doi:10.1007/978-1-4899-0056-2_4

Cited by 4 publications

(3 citation statements)

References 10 publications

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“…Because the local volume increase in the microvessels at that site occurs as early as the HbR increase (Malonek et al, 1997), the above consideration may also shed some light on the "initial dip" (i.e., a negative BOLD polarity) analyzed in some fMRI studies Hennig et al, 1997;Hu et al, 1997;Kim et al, 2000). This effect may be caused by special initial conditions in which an increase of HbR driving the BOLD signal in negative direction is stronger than a concomitant volume increase driving it into positive direction.…”

Section: Hemodynamics and The Bold Effectmentioning

confidence: 98%

New Insights into the Hemodynamic Blood Oxygenation Level-Dependent Response through Combination of Functional Magnetic Resonance Imaging and Optical Recording in Gerbil Barrel Cortex

et al. 2000

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Fast, low-angle shoot functional magnetic resonance imaging (fMRI), based on the blood oxygenation level-dependent (BOLD) effect, was combined with optical recording of intrinsic signals (ORIS) and 2-deoxyglucose labeling in gerbil barrel cortex. We observed over the activated barrel a positive BOLD signal and increased levels of deoxyhemoglobin and total hemoglobin during each period of prolonged (30 sec) D2 vibrissal stimulation. These data show that the hemodynamic basis of this fMRI signal is not necessarily a washout of deoxyhemoglobin, as generally assumed. Instead, they suggest that a positive BOLD signal can also be caused by a local increase of blood volume, even if deoxyhemoglobin levels are persistently elevated. We also show that this alternative interpretation is consistent with theoretical models of the BOLD signal. The changes in BOLD signal and blood volume, which are most tightly correlated with the periodic stimulation, peak at the site of neuronal activation. These results contribute to the understanding of the hemodynamic mechanisms underlying the BOLD signal and also suggest analysis methods, which improve the spatial localization of neuronal activation with both fMRI and ORIS.

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Section: Hemodynamics and The Bold Effectmentioning

confidence: 98%

New Insights into the Hemodynamic Blood Oxygenation Level-Dependent Response through Combination of Functional Magnetic Resonance Imaging and Optical Recording in Gerbil Barrel Cortex

et al. 2000

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“…• Observation of the pre-undershoot in fMRI (Hennig et al 1997;Hu et al 1997;Menon et al 1995) and correlation with optical imaging (Malonek and Grinvald 1996) was reported. This is still highly controversial as the effect is very subtle and the hypothesized mechanisms producing it (rapid change in blood volume or ∆CMRO 2 ) remain hotly debated.…”

Section: Advancesmentioning

confidence: 96%

Functional MRI Limitations and Aspirations

Bandettini

2009

Neural Correlates of Thinking

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PrefaceThe idea of the present book emerged on the island of Elba in the summer of 2006 during an enjoyable and very fruitful workshop on thinking with the participation of most of the contributors of the present volume.The main intention behind the book is to address thinking by surveying the contribution of various functional neuroimaging methods to our understanding of the neural underpinnings of thinking. The major focus is on the methods applicable to the neurobiological study of human thinking, since much of what we consider complex thinking has to be considered as a part of the distinctive features of human nature.Despite the fact that we are far from a full understanding of the modularity of the human brain, the use of functional imaging techniques is obviously based on the premise that brain functions are modular.We are grateful to the distinguished authors, coming from different backgrounds, for their commitment to this project, which represents a true interdisciplinary approach, as is mandatory for this fascinating and challenging topic. We are also proud to have been able to recruit an outstanding worldwide team of contributors.We also wish to thank Anette Lindqvist and Dieter Czechlik from Springer Science+Business Media for their enthusiasm and constant support. Without their optimism and tireless efforts this volume would not have been possible. Munich, GermanyEduard Abstract Most would agree that knowing precisely what was happening in the brain during the act of thinking would help in our pursuit to understand what thinking really is. This chapter describes the basics, limits, and future directions of one of the more effective tools we have to observe the human brain while it is functioningfunctional MRI. Functional MRI emerged in the early 1990s, and has since grown explosively in utility. In this chapter, an in-depth exploration is carried out of what limits functional MRI to a spatial resolution of millimeters and a temporal resolution of seconds. In addition, issues of how sensitive functional MRI is in detecting brain activity and how deeply we can interpret the signal changes are explored. Lastly, the chapter ends with a discussion on how imaging might be essential, or perhaps irrelevant, to understanding thinking.

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“…Early dip responses to activation seem to be confirmed with a number of different studies, but some questions still remain unanswered. [6][7][8][9][10] Nevertheless, the dip and post-stimulus undershoot do not seem to be there all the time and the results, therefore, remain contentious. In addition, for animal studies, the presence and absence of overshoot and undershoot seem to be also dependent on the anesthetic agents used.…”

Section: Major Research Issues and Open Ques-tionsmentioning

confidence: 99%

A current perspective of the status of understanding BOLD imaging and its use in studying brain function: a summary of the workshop at the University of North Carolina in Chapel Hill, 26–28 October, 2000

Haacke

Lin

et al. 2001

NMR in Biomedicine

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Is There a Different Type of MR-Contrast in the Early Phase of Functional Activation?

Cited by 4 publications

References 10 publications

New Insights into the Hemodynamic Blood Oxygenation Level-Dependent Response through Combination of Functional Magnetic Resonance Imaging and Optical Recording in Gerbil Barrel Cortex

New Insights into the Hemodynamic Blood Oxygenation Level-Dependent Response through Combination of Functional Magnetic Resonance Imaging and Optical Recording in Gerbil Barrel Cortex

Functional MRI Limitations and Aspirations

A current perspective of the status of understanding BOLD imaging and its use in studying brain function: a summary of the workshop at the University of North Carolina in Chapel Hill, 26–28 October, 2000

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