scholarly journals Cortical Depth-Dependent Temporal Dynamics of the BOLD Response in the Human Brain

2011 ◽  
Vol 31 (10) ◽  
pp. 1999-2008 ◽  
Author(s):  
Jeroen CW Siero ◽  
Natalia Petridou ◽  
Hans Hoogduin ◽  
Peter R Luijten ◽  
Nick F Ramsey
Keyword(s):  
Human Brain ◽  
Gray Matter ◽  
Animal Studies ◽  
Temporal Dynamics ◽  
Onset Time ◽  
Neurovascular Coupling ◽  
Blood Oxygen Level Dependent ◽  
Peak Time ◽  
Blood Oxygen Level ◽  
Coupling Mechanisms

Recent animal studies at high field have shown that blood oxygen level-dependent (BOLD) contrast can be specific to the laminar vascular architecture of the cortex, by differences in its temporal dynamics in reference to cortical depth. In this study, we characterize the temporal dynamics of the hemodynamic response (HDR) across cortical depth in the human primary motor and visual cortex, at 7T and using very short stimuli and with high spatial and temporal resolution. We find that the shape and temporal dynamics of the HDR changed in an orderly manner across cortical depth. Compared with the pial vasculature, HDRs in deeper gray matter are significantly faster in onset time (by ∼ 0.5 second) and peak time (∼2 seconds), and are narrower (by ∼1 second) and with smaller amplitude, in line with the known vascular organization across cortical depth and the transit of deoxygenated blood through the vasculature. The width of the HDR in deeper gray matter was as short as 2.1 seconds, indicating that neurovascular coupling takes place at a shorter timescale than previously reported in the human brain. These findings open the possibility to probe layer-specific hemodynamics and neurovascular coupling mechanisms in human gray matter.

No evidence for the involvement of serotonin or the 5-HTTLPR genotype in intertemporal choice in a larger community sample

2019 ◽  
Vol 33 (11) ◽  
pp. 1377-1387
Author(s):  
Philipp T Neukam ◽  
Yacila I Deza-Araujo ◽  
Michael Marxen ◽  
Shakoor Pooseh ◽  
Marcella Rietschel ◽  
...  
Keyword(s):  
Animal Studies ◽  
Intertemporal Choice ◽  
Community Sample ◽  
Temporal Discounting ◽  
Blood Oxygen Level Dependent ◽  
Choice Task ◽  
Blood Oxygen Level ◽  
Double Blind ◽  
Theoretical Approaches ◽  
S Allele

Background: Serotonin has been implicated in impulsive behaviours such as temporal discounting. While animal studies and theoretical approaches suggest that reduced tonic serotonin levels increase temporal discounting rates and vice versa, evidence from human studies is scarce and inconclusive. Furthermore, an important modulator of serotonin signalling, a genetic variation in the promoter region of the serotonin transporter gene ( 5-HTTLPR), has not been investigated for temporal discounting so far. Objective: First, the purpose of this study was to test for a significant association between 5-HTTLPR and temporal discounting. Second, we wished to investigate the effect of high/low tonic serotonin levels on intertemporal choice and blood oxygen-level-dependent response, controlling for 5-HTTLPR. Methods: We tested the association of 5-HTTLPR with temporal discounting rates using an intertemporal choice task in 611 individuals. We then manipulated tonic serotonin levels with acute tryptophan interventions (depletion, loading, balanced) in a subsample of 45 short (S)-allele and 45 long (L)/L-allele carriers in a randomised double-blind crossover design using functional magnetic resonance imaging and an intertemporal choice task. Results: Overall, we did not find any effect of serotonin and 5-HTTLPR on temporal discounting rates or the brain networks associated with valuation and cognitive control. Conclusion: Our findings indicate that serotonin may not be directly involved in choices including delays on longer timescales such as days, weeks or months. We speculate that serotonin plays a stronger role in dynamic intertemporal choice tasks where the delays are on a timescale of seconds and hence are therefore directly experienced during the experiment.

scholarly journals Similarities and Differences in Arterial Responses to Hypercapnia and Visual Stimulation

2010 ◽  
Vol 31 (2) ◽  
pp. 560-571 ◽  
Author(s):  
Yi-Ching Lynn Ho ◽  
Esben Thade Petersen ◽  
Ivan Zimine ◽  
Xavier Golay
Keyword(s):  
Blood Volume ◽  
Transit Time ◽  
Gray Matter ◽  
Visual Stimulation ◽  
Vascular System ◽  
Blood Oxygen Level Dependent ◽  
Blood Oxygen Level ◽  
Functional Studies ◽  
Arterial Blood ◽  
Arterial Blood Volume

Despite the different origins of cerebrovascular activity induced by neurogenic and nonneurogenic conditions, a standard assumption in functional studies is that the consequence on the vascular system will be mechanically similar. Using a recently developed arterial spin labeling method, we examined arterial blood volume, arterial-microvascular transit time, and cerebral blood flow (CBF) in the gray matter and in areas with large arterial vessels under hypercapnia, visual stimulation, and a combination of the two. Spatial heterogeneity in arterial reactivity was observed between conditions. During hypercapnia, large arterial volume changes contributed to CBF increase and further downstream, there were reductions in the gray matter transit time. These changes were not significant during visual stimulation, and during the combined condition they were moderated. These findings suggest distinct vascular mechanisms for large and small arterial segments that may be condition specific. However, the power relationships between gray matter arterial blood volume and CBF in hypercapnia (α = 0.69 ± 0.24) and visual stimulation (α = 0.68 ± 0.20) were similar. Assuming consistent capillary and venous volume responses across these conditions, these results offer support for a consistent total CBV–flow relationship typically assumed in blood oxygen-level dependent calibration techniques.

scholarly journals The Significance of Echo Time in fMRI BOLD Contrast: A Clinical Study during Motor and Visual Activation Tasks at 1.5 T

Tomography ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 333-343
Author(s):  
Themistoklis Boursianis ◽  
Georgios Kalaitzakis ◽  
Katerina Nikiforaki ◽  
Emmanouela Kosteletou ◽  
Despina Antypa ◽  
...  
Keyword(s):  
Gray Matter ◽  
Brain Function ◽  
Blood Oxygen Level Dependent ◽  
Small Scale ◽  
Blood Oxygen Level ◽  
Specific Sequence ◽  
Visual Cortices ◽  
Echo Time ◽  
Sequence Parameters ◽  
Larger Sample

Blood Oxygen Level Dependent (BOLD) is a commonly-used MR imaging technique in studying brain function. The BOLD signal can be strongly affected by specific sequence parameters, especially in small field strengths. Previous small-scale studies have investigated the effect of TE on BOLD contrast. This study evaluates the dependence of fMRI results on echo time (TE) during concurrent activation of the visual and motor cortex at 1.5 T in a larger sample of 21 healthy volunteers. The experiment was repeated using two different TE values (50 and 70 ms) in counterbalanced order. Furthermore, T2* measurements of the gray matter were performed. Results indicated that both peak beta value and number of voxels were significantly higher using TE = 70 than TE = 50 ms in primary motor, primary somatosensory and supplementary motor cortices (p < 0.007). In addition, the amplitude of activation in visual cortices and the dorsal premotor area was also higher using TE = 70 ms (p < 0.001). Gray matter T2* of the corresponding areas did not vary significantly. In conclusion, the optimal TE value (among the two studied) for visual and motor activity is 70 ms affecting both the amplitude and extent of regional hemodynamic activation.

scholarly journals A Model of the Dynamic Relationship between Blood Flow and Volume Changes during Brain Activation

2004 ◽  
Vol 24 (12) ◽  
pp. 1382-1392 ◽  
Author(s):  
Yazhuo Kong ◽  
Ying Zheng ◽  
David Johnston ◽  
John Martindale ◽  
Myles Jones ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Volume ◽  
Temporal Dynamics ◽  
Blood Oxygen Level Dependent ◽  
Extended Model ◽  
Biophysical Modeling ◽  
Blood Oxygen Level ◽  
Windkessel Model ◽  
Dynamic Relationship ◽  
Dependent Signal

The temporal relationship between changes in cerebral blood flow (CBF) and cerebral blood volume (CBV) is important in the biophysical modeling and interpretation of the hemodynamic response to activation, particularly in the context of magnetic resonance imaging and the blood oxygen level–dependent signal. Grubb et al. (1974) measured the steady state relationship between changes in CBV and CBF after hypercapnic challenge. The relationship CBVαCBFΦ has been used extensively in the literature. Two similar models, the Balloon ( Buxton et al., 1998 ) and the Windkessel ( Mandeville et al., 1999 ), have been proposed to describe the temporal dynamics of changes in CBV with respect to changes in CBF. In this study, a dynamic model extending the Windkessel model by incorporating delayed compliance is presented. The extended model is better able to capture the dynamics of CBV changes after changes in CBF, particularly in the return-to-baseline stages of the response.

scholarly journals Neurovascular Coupling in Development and Disease: Focus on Astrocytes

2021 ◽  
Vol 9 ◽  
Author(s):  
Teresa L. Stackhouse ◽  
Anusha Mishra
Keyword(s):  
Blood Flow ◽  
Energy Demand ◽  
Neurovascular Unit ◽  
Neurovascular Coupling ◽  
Time Frame ◽  
Blood Oxygen Level Dependent ◽  
High Energy ◽  
Neural Activation ◽  
Blood Oxygen Level ◽  
Similar Time

Neurovascular coupling is a crucial mechanism that matches the high energy demand of the brain with a supply of energy substrates from the blood. Signaling within the neurovascular unit is responsible for activity-dependent changes in cerebral blood flow. The strength and reliability of neurovascular coupling form the basis of non-invasive human neuroimaging techniques, including blood oxygen level dependent (BOLD) functional magnetic resonance imaging. Interestingly, BOLD signals are negative in infants, indicating a mismatch between metabolism and blood flow upon neural activation; this response is the opposite of that observed in healthy adults where activity evokes a large oversupply of blood flow. Negative neurovascular coupling has also been observed in rodents at early postnatal stages, further implying that this is a process that matures during development. This rationale is consistent with the morphological maturation of the neurovascular unit, which occurs over a similar time frame. While neurons differentiate before birth, astrocytes differentiate postnatally in rodents and the maturation of their complex morphology during the first few weeks of life links them with synapses and the vasculature. The vascular network is also incomplete in neonates and matures in parallel with astrocytes. Here, we review the timeline of the structural maturation of the neurovascular unit with special emphasis on astrocytes and the vascular tree and what it implies for functional maturation of neurovascular coupling. We also discuss similarities between immature astrocytes during development and reactive astrocytes in disease, which are relevant to neurovascular coupling. Finally, we close by pointing out current gaps in knowledge that must be addressed to fully elucidate the mechanisms underlying neurovascular coupling maturation, with the expectation that this may also clarify astrocyte-dependent mechanisms of cerebrovascular impairment in neurodegenerative conditions in which reduced or negative neurovascular coupling is noted, such as stroke and Alzheimer’s disease.

scholarly journals Non-linear frequency-dependence of neurovascular coupling in the cerebellar cortex implies vasodilation-vasoconstriction competition

2021 ◽  
Author(s):  
Giuseppe Gagliano ◽  
Anita Monteverdi ◽  
Stefano Casali ◽  
Umberto Laforenza ◽  
Claudia A.M. Gandini Wheeler-Kingshott ◽  
...  
Keyword(s):  
Frequency Dependence ◽  
Time Course ◽  
Mossy Fiber ◽  
Neurovascular Coupling ◽  
Blood Oxygen Level Dependent ◽  
Electrode Arrays ◽  
Blood Oxygen Level ◽  
Linear Frequency ◽  
Non Linear ◽  
Capillary Dynamics

Neurovascular coupling (NVC) is the process associating local cerebral blood flow (CBF) to neuronal activity (NA). Although NVC provides the basis for the blood-oxygen-level-dependent (BOLD) effect used in functional MRI (fMRI), the relationship between NVC and NA is still unclear. Since recent studies reported cerebellar non-linearities in BOLD signals during motor tasks execution, we investigated the NVC/NA relationship using a range of input frequencies in acute mouse cerebellar slices of vermis and hemisphere. The capillary diameter increased in response to mossy fiber activation in the 6-300Hz range, with a marked inflection around 50Hz (vermis) and 100Hz (hemisphere). The corresponding NA was recorded using high-density multi-electrode arrays and correlated to capillary dynamics through a computational model dissecting the main components of granular layer activity. Here, NVC is known to involve a balance between the NMDAR-NO pathway driving vasodilation and the mGluRs-20HETE pathway driving vasoconstriction. Simulations showed that the NMDAR-mediated component of NA was sufficient to explain the time-course of the capillary dilation but not its non-linear frequency-dependence, suggesting that the mGluRs-20HETE pathway plays a role at intermediate frequencies. These parallel control pathways imply a vasodilation-vasoconstriction competition hypothesis that could adapt local hemodynamics at the microscale bearing implications for fMRI signals interpretation.

scholarly journals Mesoscopic Mapping of Ictal Neurovascular Coupling in Awake Behaving Mice Using Optical Spectroscopy and Genetically Encoded Calcium Indicators

2021 ◽  
Vol 15 ◽  
Author(s):  
Fan Yang ◽  
Jing Li ◽  
Yan Song ◽  
Mingrui Zhao ◽  
James E. Niemeyer ◽  
...  
Keyword(s):  
Cerebral Blood Volume ◽  
Imaging Techniques ◽  
Neurovascular Coupling ◽  
Blood Oxygen Level Dependent ◽  
Epileptic Focus ◽  
Wide Field ◽  
Blood Oxygen Level ◽  
Optical Signals ◽  
Hemoglobin Oxygenation ◽  
Mapping Techniques

Unambiguously identifying an epileptic focus with high spatial resolution is a challenge, especially when no anatomic abnormality can be detected. Neurovascular coupling (NVC)-based brain mapping techniques are often applied in the clinic despite a poor understanding of ictal NVC mechanisms, derived primarily from recordings in anesthetized animals with limited spatial sampling of the ictal core. In this study, we used simultaneous wide-field mesoscopic imaging of GCamp6f and intrinsic optical signals (IOS) to record the neuronal and hemodynamic changes during acute ictal events in awake, behaving mice. Similar signals in isoflurane-anesthetized mice were compared to highlight the unique characteristics of the awake condition. In awake animals, seizures were more focal at the onset but more likely to propagate to the contralateral hemisphere. The HbT signal, derived from an increase in cerebral blood volume (CBV), was more intense in awake mice. As a result, the “epileptic dip” in hemoglobin oxygenation became inconsistent and unreliable as a mapping signal. Our data indicate that CBV-based imaging techniques should be more accurate than blood oxygen level dependent (BOLD)-based imaging techniques for seizure mapping in awake behaving animals.

scholarly journals Relationship Between Changes in the Temporal Dynamics of the Blood-Oxygen-Level-Dependent Signal and Hypoperfusion in Acute Ischemic Stroke

Stroke ◽  
2017 ◽  
Vol 48 (4) ◽  
pp. 925-931 ◽  
Author(s):  
Ahmed A. Khalil ◽  
Ann-Christin Ostwaldt ◽  
Till Nierhaus ◽  
Ramanan Ganeshan ◽  
Heinrich J. Audebert ◽  
...  
Keyword(s):  
Ischemic Stroke ◽  
Acute Ischemic Stroke ◽  
Temporal Dynamics ◽  
Blood Oxygen Level Dependent ◽  
Blood Oxygen ◽  
Oxygen Level ◽  
Blood Oxygen Level ◽  
Dependent Signal

scholarly journals Faster than thought: Detecting sub-second activation sequences with sequential fMRI pattern analysis

2020 ◽  
Author(s):  
Lennart Wittkuhn ◽  
Nicolas W. Schuck
Keyword(s):  
Human Brain ◽  
Time Scales ◽  
Temporal Cortex ◽  
Blood Oxygen Level Dependent ◽  
Blood Oxygen Level ◽  
Activation Patterns ◽  
Neural Computations ◽  
Time Courses ◽  
Human Participants ◽  
Ventral Temporal Cortex

AbstractNeural computations are often anatomically localized and executed on sub-second time scales. Understanding the brain therefore requires methods that offer sufficient spatial and temporal resolution. This poses a particular challenge for the study of the human brain because non-invasive methods have either high temporal or spatial resolution, but not both. Here, we introduce a novel multivariate analysis method for conventional blood-oxygen-level dependent functional magnetic resonance imaging (BOLD fMRI) that allows to study sequentially activated neural patterns separated by less than 100 ms with anatomical precision. Human participants underwent fMRI and were presented with sequences of visual stimuli separated by 32 to 2048 ms. Probabilistic pattern classifiers were trained on fMRI data to detect the presence of image-specific activation patterns in early visual and ventral temporal cortex. The classifiers were then applied to data recorded during sequences of the same images presented at increasing speeds. Our results show that probabilistic classifier time courses allowed to detect neural representations and their order, even when images were separated by only 32 ms. Moreover, the frequency spectrum of the statistical sequentiality metric distinguished between sequence speeds on sub-second versus supra-second time scales. These results survived when data with high levels of noise and rare sequence events at unknown times were analyzed. Our method promises to lay the groundwork for novel investigations of fast neural computations in the human brain, such as hippocampal replay.

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