Functional spectroscopy of brain activation following a single light pulse: Examinations of the mechanism of the fast initial response

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

doi:10.1002/ima.1850060210

Cited by 48 publications

(34 citation statements)

References 12 publications

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“…Our results obtained from the rat somatosensory cor tex contrast with those of fMRI experiments in the hu man visual cortex (Ernst and Hennig, 1994;Menon et al, 1995;Hennig et al, 1995;Hu et al, 1997;Janz et al, 1997). This discrepancy may be due to a number of factors including different species, vessel architectures, venous oxygenation level, and oxygen consumption, namely, different anatomical and physiological param eters that could affect the BOLD signal changes elicited by neuronal stimulation in each species.…”

Section: Discussioncontrasting

confidence: 92%

Early Temporal Characteristics of Cerebral Blood Flow and Deoxyhemoglobin Changes during Somatosensory Stimulation

Silva

Lee

Iadecola

et al. 2000

J Cereb Blood Flow Metab

160

143

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Summary:The close correspondence between neural activity in the brain and cerebral blood flow (CBF) forms the basis for modern functional neuroimaging methods, Yet, the temporal characteristics of hemodynamic changes induced by neuronal activity are not well understood, Recent optical imaging obser vations of the time course of de oxyhemoglobin (HbR) and oxyhemoglobin have suggested that increases in oxygen con sumption after neuronal activation occur earlier and are more spatially localized than the delayed and more diffuse CBF re sponse, Deoxyhemoglobin can be detected by blood oxygen ation level-dependent (BOLD) functional magnetic resonance imaging (fMRI), In the present study, the temporal character istics of CBF and BOLD changes elicited by somatosensory stimulation in rat were investigated by high-field (9A T) MRLThe tight coupling between neural activity and cere bral blood flow (CBF) (Roy and Sherrington, 1890) forms the basis for modern functional neuroimaging methods (Raichle, 1998), However, despite widespread use of hemodynamic changes as a surrogate for neuronal activity, the temporal relationship between neural activ ity, tissue oxygenation, and CBF is not well understood (Iadecola, 1993), Recent optical imaging observations of the time course of deoxyhemoglobin (HbR) and oxyhemoglobin (Hb02) changes during visual stimulation in the cat stri ate cortex have provided evidence of a biphasic behavior 201With use of high-temporal-resolution fMRI, it was found that the onset time of the CBF response in the somatosensory cortex was 0,6 ± OA seconds (n = 10), The CBF changes occurred significantly earlier than changes in HbR concentration, which responded after I, I ± 0,3 seconds, Furthermore, no early in creases in HbR (early negative BOLD signal changes) were observed, These findings argue against the occurrence of an early loss of hemoglobin oxygenation that precedes the rise in CBF and suggest that CBF and oxygen consumption increases may be dynamically coupled in this animal model of neural activation, Key Words: Cerebral blood flow-Arterial spin labeling-Echo planar imaging-Functional brain mapping Forepaw stimulation, of blood oxygenation: an early «3-second) increase in HbR after the onset of neuronal activation, followed by a decrease in HbR and a more widespread increase in Hb02 (Malonek and Grinvald, 1996;Malonek et aL, 1997), Similar findings were also observed in rat somato sensory cortex (Nemoto et aL, 1999), The initial increase in HbR was interpreted to indicate that the increases in oxygen consumption after neuronal activation occur ear lier and are more spatially localized than the delayed CBF response (Malonek and Grinvald, 1996), The early decrease in blood oxygenation after activation raises the possibility that tissue hypoxia may trigger the increase in CBF Changes in HbR can be detected by functional magnetic resonance imaging (fMRI) based on the blood oxygenation level-dependent (BOLD) contrast The im plication of these results for fMRI may be that studies based on the early nega...

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Section: Discussioncontrasting

confidence: 92%

Early Temporal Characteristics of Cerebral Blood Flow and Deoxyhemoglobin Changes during Somatosensory Stimulation

Silva

Lee

Iadecola

et al. 2000

J Cereb Blood Flow Metab

160

143

View full text Add to dashboard Cite

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“…We therefore termed the effect SEEP. Others have also suggested that there may be such a contribution to fMRI signal changes (19). However, the fMRI data we obtained in the spinal cord demonstrated that the SEEP effect is 3 times larger than that observed in the brain and enabled us to confirm its existence.…”

Section: Discussionsupporting

confidence: 49%

Functional magnetic resonance imaging of the human brain and spinal cord by means of signal enhancement by extravascular protons

Stroman

Tomanek

Malisza

2003

Concepts Magnetic Resonance

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ABSTRACT:A review of functional magnetic resonance imaging (fMRI) signal changes in spin-echo image data is presented. Spin-echo fMRI data from the human brain and spinal cord show a consistent departure from that expected with blood oxygen level dependent (BOLD) contrast. Studies to investigate this finding demonstrate fMRI signal changes of 2.5% in the spinal cord and 0.7% in the brain at 1.5 T, which is extrapolated to an echo time of zero. Consistent evidence of a non-BOLD contrast mechanism arising from a proton-density change at sites of neuronal activation is demonstrated. A mathematical model and physiological explanation for signal enhancement by extravascular protons is also presented.

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“…2), concordant with optical spectroscopic measurements in animals (33,34), which show highly localized relative deoxygenation in active columns beginning within hundreds of milliseconds. This early deoxygenation has been implicated as a mechanism of an early dip in BOLD signal that precedes the hemodynamic alterations in the first 2 sec of stimulation (35).…”

Section: Discussionmentioning

confidence: 99%

Calibrated functional MRI: Mapping the dynamics of oxidative metabolism

Davis

Kwong

Weisskoff

et al. 1998

Proc. Natl. Acad. Sci. U.S.A.

977

1,305

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MRI was extended to the measurement of changes in oxidative metabolism in the normal human during functionally induced changes in cellular activity. A noninvasive MRI method that is model-independent calibrates the blood oxygen level dependent (BOLD) signal of functional MRI (fMRI) against perfusion-sensitive MRI, using carbon dioxide breathing as a physiological reference standard. This calibration procedure provides a regional measurement of the expected sensitivity of the fMRI BOLD signal to changes in the cellular activity of the brain. Maps of the BOLD signal calibration factor showed regional heterogeneity, indicating that the magnitude of functionally induced changes in the BOLD signal will be dependent on both the local change in blood f low and the local baseline physiology of the cerebral cortex. BOLD signal magnitude is shown to be reduced by 32% from its expected level by the action of oxygen metabolism. The calibrated fMRI technique was applied to stimulation of the human visual cortex with an alternating radial checkerboard pattern. With this stimulus oxygen consumption increased 16% whereas blood f low increased 45%. Although this result is consistent with previous findings of a significant difference between the increase in blood f low and oxygen consumption, it does indicate clearly that oxidative metabolism is a significant component of the metabolic response of the brain to functionally induced changes in cellular activity.Functionally related changes in neuronal activity in the normal brain are reliably accompanied by changes in local cerebral blood flow (CBF) (1). The degree to which the cerebral metabolic rate for oxygen (CMR O2 ) also changes with activityrelated increases and decreases in neuronal activity remains controversial. Although some reports show little or no taskinduced increase in CMR O2 (2-4), others have shown varying degrees of coupling of oxidative metabolism to glucose consumption and blood flow (5-7), both of which increase dramatically with task activation (3,4,8). Some have suggested that the reason CBF changes more than CMR O2 during functionally related increases in neuronal activity (decreases have not been addressed) is to enhance the diffusion-limited delivery of oxygen to the tissue (9-11).Current functional MRI (fMRI) methods rely on the fact that CBF changes more than CMR O2 , producing localized changes in tissue oxygen content. These localized changes in tissue oxygen content change magnetic fields in a manner that can be detected with MRI. This signal has been termed the blood oxygen level dependent (BOLD) signal of fMRI (12, 13). The fMRI BOLD signal has been viewed as a reasonable marker of functionally related changes in neuronal activity. The magnitude of the BOLD signal, of course, is dependent on the relationship between changes, if any, in CMR O2 and the changes in CBF. The greater the increase in CMR O2 for any increase in CBF, the smaller the BOLD signal becomes and vice versa.In this paper we examine the degree to which the relationship betw...

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Functional spectroscopy of brain activation following a single light pulse: Examinations of the mechanism of the fast initial response

Cited by 48 publications

References 12 publications

Early Temporal Characteristics of Cerebral Blood Flow and Deoxyhemoglobin Changes during Somatosensory Stimulation

Early Temporal Characteristics of Cerebral Blood Flow and Deoxyhemoglobin Changes during Somatosensory Stimulation

Functional magnetic resonance imaging of the human brain and spinal cord by means of signal enhancement by extravascular protons

Calibrated functional MRI: Mapping the dynamics of oxidative metabolism

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