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Das A, Murphy K, Drew PJ. Rude mechanicals in brain haemodynamics: non-neural actors that influence blood flow. Philos Trans R Soc Lond B Biol Sci 2021; 376:20190635. [PMID: 33190603 PMCID: PMC7741032 DOI: 10.1098/rstb.2019.0635] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/15/2020] [Indexed: 01/10/2023] Open
Abstract
Fluctuations in blood oxygenation and flow are widely used to infer brain activity during resting-state functional magnetic resonance imaging (fMRI). However, there are strong systemic and vascular contributions to resting-state signals that are unrelated to ongoing neural activity. Importantly, these non-neural contributions to haemodynamic signals (or 'rude mechanicals') can be as large as or larger than the neurally evoked components. Here, we review the two broad classes of drivers of these signals. One is systemic and is tied to fluctuations in external drivers such as heart rate and breathing, and the robust autoregulatory mechanisms that try to maintain a constant milieu in the brain. The other class comprises local, active fluctuations that appear to be intrinsic to vascular tissue and are likely similar to active local fluctuations seen in vasculature all over the body. In this review, we describe these non-neural fluctuations and some of the tools developed to correct for them when interpreting fMRI recordings. However, we also emphasize the links between these vascular fluctuations and brain physiology and point to ways in which fMRI measurements can be used to exploit such links to gain valuable information about neurovascular health and about internal brain states. This article is part of the theme issue 'Key relationships between non-invasive functional neuroimaging and the underlying neuronal activity'.
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Affiliation(s)
- Aniruddha Das
- Department of Neuroscience, Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA
| | - Kevin Murphy
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Physics and Astronomy, Cardiff University, Cardiff CF24 4HQ, UK
| | - Patrick J. Drew
- Departments of Engineering Science and Mechanics, Neurosurgery, and Biomedical Engineering, The Pennsylvania State University, University Park, PA 16802, USA
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Drew PJ, Mateo C, Turner KL, Yu X, Kleinfeld D. Ultra-slow Oscillations in fMRI and Resting-State Connectivity: Neuronal and Vascular Contributions and Technical Confounds. Neuron 2020; 107:782-804. [PMID: 32791040 PMCID: PMC7886622 DOI: 10.1016/j.neuron.2020.07.020] [Citation(s) in RCA: 76] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 06/09/2020] [Accepted: 07/15/2020] [Indexed: 12/27/2022]
Abstract
Ultra-slow, ∼0.1-Hz variations in the oxygenation level of brain blood are widely used as an fMRI-based surrogate of "resting-state" neuronal activity. The temporal correlations among these fluctuations across the brain are interpreted as "functional connections" for maps and neurological diagnostics. Ultra-slow variations in oxygenation follow a cascade. First, they closely track changes in arteriole diameter. Second, interpretable functional connections arise when the ultra-slow changes in amplitude of γ-band neuronal oscillations, which are shared across even far-flung but synaptically connected brain regions, entrain the ∼0.1-Hz vasomotor oscillation in diameter of local arterioles. Significant confounds to estimates of functional connectivity arise from residual vasomotor activity as well as arteriole dynamics driven by self-generated movements and subcortical common modulatory inputs. Last, methodological limitations of fMRI can lead to spurious functional connections. The neuronal generator of ultra-slow variations in γ-band amplitude, including that associated with self-generated movements, remains an open issue.
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Affiliation(s)
- Patrick J Drew
- Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA 16802, USA; Department of Biomedical Engineering, Pennsylvania State University, University Park, PA 16802, USA; Department of Neurosurgery, Pennsylvania State University, University Park, PA 16802, USA
| | - Celine Mateo
- Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA
| | - Kevin L Turner
- Department of Biomedical Engineering, Pennsylvania State University, University Park, PA 16802, USA
| | - Xin Yu
- High-Field Magnetic Resonance Department, Max Planck Institute for Biological Cybernetics, 72076 Tübingen, Germany; MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Charlestown, MA 02114, USA
| | - David Kleinfeld
- Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA; Section of Neurobiology, University of California, San Diego, La Jolla, CA 92093, USA.
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Bright MG, Whittaker JR, Driver ID, Murphy K. Vascular physiology drives functional brain networks. Neuroimage 2020; 217:116907. [PMID: 32387624 PMCID: PMC7339138 DOI: 10.1016/j.neuroimage.2020.116907] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 04/27/2020] [Accepted: 05/03/2020] [Indexed: 12/12/2022] Open
Abstract
We present the first evidence for vascular regulation driving fMRI signals in specific functional brain networks. Using concurrent neuronal and vascular stimuli, we collected 30 BOLD fMRI datasets in 10 healthy individuals: a working memory task, flashing checkerboard stimulus, and CO2 inhalation challenge were delivered in concurrent but orthogonal paradigms. The resulting imaging data were averaged together and decomposed using independent component analysis, and three "neuronal networks" were identified as demonstrating maximum temporal correlation with the neuronal stimulus paradigms: Default Mode Network, Task Positive Network, and Visual Network. For each of these, we observed a second network component with high spatial overlap. Using dual regression in the original 30 datasets, we extracted the time-series associated with these network pairs and calculated the percent of variance explained by the neuronal or vascular stimuli using a normalized R2 parameter. In each pairing, one network was dominated by the appropriate neuronal stimulus, and the other was dominated by the vascular stimulus as represented by the end-tidal CO2 time-series recorded in each scan. We acquired a second dataset in 8 of the original participants, where no CO2 challenge was delivered and CO2 levels fluctuated naturally with breathing variations. Although splitting of functional networks was not robust in these data, performing dual regression with the network maps from the original analysis in this new dataset successfully replicated our observations. Thus, in addition to responding to localized metabolic changes, the brain's vasculature may be regulated in a coordinated manner that mimics (and potentially supports) specific functional brain networks. Multi-modal imaging and advances in fMRI acquisition and analysis could facilitate further study of the dual nature of functional brain networks. It will be critical to understand network-specific vascular function, and the behavior of a coupled vascular-neural network, in future studies of brain pathology.
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Affiliation(s)
- Molly G Bright
- Department of Physical Therapy and Human Movement Science, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA; Department of Biomedical Engineering, McCormick School of Engineering and Applied Sciences, Northwestern University, Evanston, IL, 60201, USA.
| | - Joseph R Whittaker
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, United Kingdom
| | - Ian D Driver
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff, CF10 3AT, United Kingdom
| | - Kevin Murphy
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, United Kingdom
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Lee RH, Couto E Silva A, Lerner FM, Wilkins CS, Valido SE, Klein DD, Wu CY, Neumann JT, Della-Morte D, Koslow SH, Minagar A, Lin HW. Interruption of perivascular sympathetic nerves of cerebral arteries offers neuroprotection against ischemia. Am J Physiol Heart Circ Physiol 2016; 312:H182-H188. [PMID: 27864234 DOI: 10.1152/ajpheart.00482.2016] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Revised: 11/11/2016] [Accepted: 11/16/2016] [Indexed: 11/22/2022]
Abstract
Sympathetic nervous system activity is increased after cardiopulmonary arrest, resulting in vasoconstrictor release from the perivascular sympathetic nerves of cerebral arteries. However, the pathophysiological function of the perivascular sympathetic nerves in the ischemic brain remains unclear. A rat model of global cerebral ischemia (asphyxial cardiac arrest, ACA) was used to investigate perivascular sympathetic nerves of cerebral arteries via bilateral decentralization (preganglionic lesion) of the superior cervical ganglion (SCG). Decentralization of the SCG 5 days before ACA alleviated hypoperfusion and afforded hippocampal neuroprotection and improved functional outcomes. These studies can provide further insights into the functional mechanism(s) of the sympathetic nervous system during ischemia. NEW & NOTEWORTHY Interruption of the perivascular sympathetic nerves can alleviate CA-induced hypoperfusion and neuronal cell death in the CA1 region of the hippocampus to enhance functional learning and memory.
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Affiliation(s)
- Reggie H Lee
- Cerebral Vascular Disease Laboratories, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, Louisiana State University Health Sciences Center, Shreveport, Louisiana
| | - Alexandre Couto E Silva
- Cerebral Vascular Disease Laboratories, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, Louisiana State University Health Sciences Center, Shreveport, Louisiana
| | - Francesca M Lerner
- Cerebral Vascular Disease Laboratories, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida
| | - Carl S Wilkins
- Florida International University Herbert Wertheim College of Medicine, Miami, Florida
| | - Stephen E Valido
- Cerebral Vascular Disease Laboratories, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida
| | - Daniel D Klein
- Cerebral Vascular Disease Laboratories, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida
| | - Celeste Y Wu
- Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, Louisiana State University Health Sciences Center, Shreveport, Louisiana
| | - Jake T Neumann
- Department of Biomedical Sciences, West Virginia School of Osteopathic Medicine, Lewisburg, West Virginia
| | - David Della-Morte
- Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida.,Department of Systems Medicine, University of Rome Tor Vergata; and.,IRCCS San Raffaele Pisana, Rome, Italy
| | - Stephen H Koslow
- Department of Psychiatry and Behavioral Sciences, University of Miami Miller School of Medicine, Miami, Florida
| | - Alireza Minagar
- Department of Neurology, Louisiana State University Health Sciences Center, Shreveport, Louisiana
| | - Hung Wen Lin
- Cerebral Vascular Disease Laboratories, University of Miami Miller School of Medicine, Miami, Florida; .,Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida.,Department of Neurology, Louisiana State University Health Sciences Center, Shreveport, Louisiana
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