101
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Hall CN, Howarth C, Kurth-Nelson Z, Mishra A. Interpreting BOLD: towards a dialogue between cognitive and cellular neuroscience. Philos Trans R Soc Lond B Biol Sci 2017; 371:rstb.2015.0348. [PMID: 27574302 DOI: 10.1098/rstb.2015.0348] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/11/2016] [Indexed: 12/11/2022] Open
Abstract
Cognitive neuroscience depends on the use of blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to probe brain function. Although commonly used as a surrogate measure of neuronal activity, BOLD signals actually reflect changes in brain blood oxygenation. Understanding the mechanisms linking neuronal activity to vascular perfusion is, therefore, critical in interpreting BOLD. Advances in cellular neuroscience demonstrating differences in this neurovascular relationship in different brain regions, conditions or pathologies are often not accounted for when interpreting BOLD. Meanwhile, within cognitive neuroscience, the increasing use of high magnetic field strengths and the development of model-based tasks and analyses have broadened the capability of BOLD signals to inform us about the underlying neuronal activity, but these methods are less well understood by cellular neuroscientists. In 2016, a Royal Society Theo Murphy Meeting brought scientists from the two communities together to discuss these issues. Here, we consolidate the main conclusions arising from that meeting. We discuss areas of consensus about what BOLD fMRI can tell us about underlying neuronal activity, and how advanced modelling techniques have improved our ability to use and interpret BOLD. We also highlight areas of controversy in understanding BOLD and suggest research directions required to resolve these issues.This article is part of the themed issue 'Interpreting BOLD: a dialogue between cognitive and cellular neuroscience'.
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Affiliation(s)
| | - Clare Howarth
- Department of Psychology, University of Sheffield, Sheffield, UK
| | - Zebulun Kurth-Nelson
- Max Planck UCL Centre for Computational Psychiatry and Ageing Research, University College London, London, UK
| | - Anusha Mishra
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK
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102
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Mateo C, Knutsen PM, Tsai PS, Shih AY, Kleinfeld D. Entrainment of Arteriole Vasomotor Fluctuations by Neural Activity Is a Basis of Blood-Oxygenation-Level-Dependent "Resting-State" Connectivity. Neuron 2017; 96:936-948.e3. [PMID: 29107517 PMCID: PMC5851777 DOI: 10.1016/j.neuron.2017.10.012] [Citation(s) in RCA: 183] [Impact Index Per Article: 26.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Revised: 09/04/2017] [Accepted: 10/05/2017] [Indexed: 01/12/2023]
Abstract
Resting-state signals in blood-oxygenation-level-dependent (BOLD) imaging are used to parcellate brain regions and define "functional connections" between regions. Yet a physiological link between fluctuations in blood oxygenation with those in neuronal signaling pathways is missing. We present evidence from studies on mouse cortex that modulation of vasomotion, i.e., intrinsic ultra-slow (0.1 Hz) fluctuations in arteriole diameter, provides this link. First, ultra-slow fluctuations in neuronal signaling, which occur as an envelope over γ-band activity, entrains vasomotion. Second, optogenetic manipulations confirm that entrainment is unidirectional. Third, co-fluctuations in the diameter of pairs of arterioles within the same hemisphere diminish to chance for separations >1.4 mm. Yet the diameters of arterioles in distant (>5 mm), mirrored transhemispheric sites strongly co-fluctuate; these correlations are diminished in acallosal mice. Fourth, fluctuations in arteriole diameter coherently drive fluctuations in blood oxygenation. Thus, entrainment of vasomotion links neuronal pathways to functional connections.
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Affiliation(s)
- Celine Mateo
- Department of Physics, University of California, San Diego, La Jolla, CA, USA
| | - Per M Knutsen
- Department of Physics, University of California, San Diego, La Jolla, CA, USA
| | - Philbert S Tsai
- Department of Physics, University of California, San Diego, La Jolla, CA, USA
| | - Andy Y Shih
- Department of Neurosciences, Medical University of South Carolina, Charleston, SC, USA
| | - David Kleinfeld
- Department of Physics, University of California, San Diego, La Jolla, CA, USA; Section of Neurobiology, University of California, San Diego, La Jolla, CA, USA.
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103
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Weak correlations between hemodynamic signals and ongoing neural activity during the resting state. Nat Neurosci 2017; 20:1761-1769. [PMID: 29184204 PMCID: PMC5816345 DOI: 10.1038/s41593-017-0007-y] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Accepted: 09/20/2017] [Indexed: 11/12/2022]
Abstract
Spontaneous fluctuations in hemodynamic signals in the absence of a task or overt stimulation are used to infer neural activity. We tested this coupling by simultaneously measuring neural activity and changes in cerebral blood volume (CBV) in the somatosensory cortex of awake, head-fixed mice during periods of true rest, and during whisker stimulation and volitional whisking. Here we show that neurovascular coupling was similar across states, and large spontaneous CBV changes in the absence of sensory input were driven by volitional whisker and body movements. Hemodynamic signals during periods of rest were weakly correlated with neural activity. Spontaneous fluctuations in CBV and vessel diameter persisted when local neural spiking and glutamatergic input was blocked, and during blockade of noradrenergic receptors, suggesting a non-neuronal origin for spontaneous CBV fluctuations. Spontaneous hemodynamic signals reflect a combination of behavior, local neural activity, and putatively non-neural processes.
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104
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Denfield GH, Fahey PG, Reimer J, Tolias AS. Investigating the Limits of Neurovascular Coupling. Neuron 2017; 91:954-956. [PMID: 27608758 DOI: 10.1016/j.neuron.2016.08.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
O'Herron et al. (2016) perform two-photon imaging of vascular and neural responses in cat and rodent primary visual cortex to investigate the limits of neurovascular coupling. Their results suggest important constraints on making inferences about neuronal responses from hemodynamic activity.
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Affiliation(s)
- George H Denfield
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Paul G Fahey
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jacob Reimer
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Andreas S Tolias
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA; Department of Computational and Applied Mathematics, Rice University, Houston, TX 77005, USA.
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105
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The Neurovascular Unit Coming of Age: A Journey through Neurovascular Coupling in Health and Disease. Neuron 2017; 96:17-42. [PMID: 28957666 DOI: 10.1016/j.neuron.2017.07.030] [Citation(s) in RCA: 1265] [Impact Index Per Article: 180.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 07/20/2017] [Accepted: 07/25/2017] [Indexed: 02/07/2023]
Abstract
The concept of the neurovascular unit (NVU), formalized at the 2001 Stroke Progress Review Group meeting of the National Institute of Neurological Disorders and Stroke, emphasizes the intimate relationship between the brain and its vessels. Since then, the NVU has attracted the interest of the neuroscience community, resulting in considerable advances in the field. Here the current state of knowledge of the NVU will be assessed, focusing on one of its most vital roles: the coupling between neural activity and blood flow. The evidence supports a conceptual shift in the mechanisms of neurovascular coupling, from a unidimensional process involving neuronal-astrocytic signaling to local blood vessels to a multidimensional one in which mediators released from multiple cells engage distinct signaling pathways and effector systems across the entire cerebrovascular network in a highly orchestrated manner. The recently appreciated NVU dysfunction in neurodegenerative diseases, although still poorly understood, supports emerging concepts that maintaining neurovascular health promotes brain health.
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106
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Gravel N, Harvey BM, Renken RJ, Dumoulin SO, Cornelissen FW. Phase-synchronization-based parcellation of resting state fMRI signals reveals topographically organized clusters in early visual cortex. Neuroimage 2017; 170:424-433. [PMID: 28867341 DOI: 10.1016/j.neuroimage.2017.08.063] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 08/02/2017] [Accepted: 08/28/2017] [Indexed: 01/29/2023] Open
Abstract
Resting-state fMRI is widely used to study brain function and connectivity. However, interpreting patterns of resting state (RS) fMRI activity remains challenging as they may arise from different neuronal mechanisms than those triggered by exogenous events. Currently, this limits the use of RS-fMRI for understanding cortical function in health and disease. Here, we examine the phase synchronization (PS) properties of blood-oxygen level dependent (BOLD) signals obtained during visual field mapping (VFM) and RS with 7T fMRI. This data-driven approach exploits spatiotemporal covariations in the phase of BOLD recordings to establish the presence of clusters of synchronized activity. We find that, in both VFM and RS data, selecting the most synchronized neighboring recording sites identifies spatially localized PS clusters that follow the topographic organization of the visual cortex. However, in activity obtained during VFM, PS is spatially more extensive than in RS activity, likely reflecting stimulus-driven interactions between local responses. Nevertheless, the similarity of the PS clusters obtained for RS and stimulus-driven fMRI suggest that they share a common neuroanatomical origin. Our finding justifies and facilitates direct comparison of RS and stimulus-evoked activity.
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Affiliation(s)
- Nicolás Gravel
- Laboratory of Experimental Ophthalmology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
| | - Ben M Harvey
- Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht, The Netherlands; Faculty of Psychology and Education Sciences, University of Coimbra, Coimbra, Portugal
| | - Remco J Renken
- NeuroImaging Center, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
| | - Serge O Dumoulin
- Faculty of Psychology and Education Sciences, University of Coimbra, Coimbra, Portugal
| | - Frans W Cornelissen
- Laboratory of Experimental Ophthalmology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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107
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Poplawsky AJ, Fukuda M, Kang BM, Kim JH, Suh M, Kim SG. Dominance of layer-specific microvessel dilation in contrast-enhanced high-resolution fMRI: Comparison between hemodynamic spread and vascular architecture with CLARITY. Neuroimage 2017; 197:657-667. [PMID: 28822749 DOI: 10.1016/j.neuroimage.2017.08.046] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Revised: 08/04/2017] [Accepted: 08/15/2017] [Indexed: 10/19/2022] Open
Abstract
Contrast-enhanced cerebral blood volume-weighted (CBVw) fMRI response peaks are specific to the layer of evoked synaptic activity (Poplawsky et al., 2015), but the spatial resolution limit of CBVw fMRI is unknown. In this study, we measured the laminar spread of the CBVw fMRI evoked response in the external plexiform layer (EPL, 265 ± 65 μm anatomical thickness, mean ± SD, n = 30 locations from 5 rats) of the rat olfactory bulb during electrical stimulation of the lateral olfactory tract and examined its potential vascular source. First, we obtained the evoked CBVw fMRI responses with a 55 × 55 μm2 in-plane resolution and a 500-μm thickness at 9.4 T, and found that the fMRI signal peaked predominantly in the inner half of EPL (136 ± 54 μm anatomical thickness). The mean full-width at half-maximum of these fMRI peaks was 347 ± 102 μm and the functional spread was approximately 100 or 200 μm when the effects of the laminar thicknesses of EPL or inner EPL were removed, respectively. Second, we visualized the vascular architecture of EPL from a different rat using a Clear Lipid-exchanged Anatomically Rigid Imaging/immunostaining-compatible Tissue hYdrogel (CLARITY)-based tissue preparation method and confocal microscopy. Microvascular segments with an outer diameter of <11 μm accounted for 64.3% of the total vascular volume within EPL and had a mean segment length of 55 ± 40 μm (n = 472). Additionally, vessels that crossed the EPL border had a mean segment length outside of EPL equal to 73 ± 61 μm (n = 28), which is comparable to half of the functional spread (50-100 μm). Therefore, we conclude that dilation of these microvessels, including capillaries, likely dominate the CBVw fMRI response and that the biological limit of the fMRI spatial resolution is approximately the average length of 1-2 microvessel segments, which may be sufficient for examining sublaminar circuits.
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Affiliation(s)
| | - Mitsuhiro Fukuda
- Neuroimaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, PA, USA.
| | - Bok-Man Kang
- Center for Neuroscience Imaging Research, Institute of Basic Science, Suwon, 440-746, Republic of Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon, 440-746, Republic of Korea
| | - Jae Hwan Kim
- Center for Neuroscience Imaging Research, Institute of Basic Science, Suwon, 440-746, Republic of Korea
| | - Minah Suh
- Center for Neuroscience Imaging Research, Institute of Basic Science, Suwon, 440-746, Republic of Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon, 440-746, Republic of Korea
| | - Seong-Gi Kim
- Center for Neuroscience Imaging Research, Institute of Basic Science, Suwon, 440-746, Republic of Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon, 440-746, Republic of Korea.
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108
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Effector-Invariant Movement Encoding in the Human Motor System. J Neurosci 2017; 37:9054-9063. [PMID: 28821649 DOI: 10.1523/jneurosci.1663-17.2017] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Revised: 07/12/2017] [Accepted: 07/24/2017] [Indexed: 01/28/2023] Open
Abstract
Ipsilateral motor areas of cerebral cortex are active during arm movements and even reliably predict movement direction. Is coding similar during ipsilateral and contralateral movements? If so, is it in extrinsic (world-centered) or intrinsic (joint-configuration) coordinates? We addressed these questions by examining the similarity of multivoxel fMRI patterns in visuomotor cortical regions during unilateral reaching movements with both arms. The results of three complementary analyses revealed that fMRI response patterns were similar across right and left arm movements to identical targets (extrinsic coordinates) in visual cortices, and across movements with equivalent joint-angles (intrinsic coordinates) in motor cortices. We interpret this as evidence for the existence of distributed neural populations in multiple motor system areas that encode ipsilateral and contralateral movements in a similar manner: according to their intrinsic/joint coordinates.SIGNIFICANCE STATEMENT Cortical motor control exhibits clear lateralization: each hemisphere controls the motor output of the contralateral body. Nevertheless, neural populations in ipsilateral areas across the visuomotor hierarchy are active during unilateral movements. We show that fMRI response patterns in the motor cortices are similar for both arms if the movement direction is mirror-reversed across the midline. This suggests that in both ipsilateral and contralateral motor cortices, neural populations have effector-invariant coding of movements in intrinsic coordinates. This not only affects our understanding of motor control, it may serve in the development of brain machine interfaces that also use ipsilateral neural activity.
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109
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Abe Y, Van Nguyen K, Tsurugizawa T, Ciobanu L, Le Bihan D. Modulation of water diffusion by activation-induced neural cell swelling in Aplysia Californica. Sci Rep 2017; 7:6178. [PMID: 28733682 PMCID: PMC5522485 DOI: 10.1038/s41598-017-05586-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Accepted: 05/31/2017] [Indexed: 01/26/2023] Open
Abstract
Diffusion functional magnetic resonance imaging (DfMRI) has been proposed as a method for functional neuroimaging studies, as an alternative to blood oxygenation level dependent (BOLD)-fMRI. DfMRI is thought to more directly reflect neural activation, but its exact mechanism remains unclear. It has been hypothesized that the water apparent diffusion coefficient (ADC) decrease observed upon neural activation results from swelling of neurons or neuron parts. To elucidate the origin of the DfMRI response at cellular level we performed diffusion MR microscopy at 17.2 T in Aplysia californica buccal ganglia and compared the water ADCs at cellular and ganglia levels before and after neuronal activation induced by perfusion with a solution containing dopamine. Neural cell swelling, evidenced from optical microscopy imaging, resulted in an intracellular ADC increase and an ADC decrease at ganglia level. Furthermore, the intracellular ADC increase was found to have a significant positive correlation with the increase in cell size. Our results strongly support the hypothesis that the ADC decrease observed with DfMRI upon neuronal activation at tissue level reflects activation-induced neural cell swelling.
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Affiliation(s)
- Yoshifumi Abe
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France
| | - Khieu Van Nguyen
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France.,University Paris-Saclay, 15 rue Georges Clemenceau, 91400, Orsay, France
| | - Tomokazu Tsurugizawa
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France
| | - Luisa Ciobanu
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France
| | - Denis Le Bihan
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France.
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110
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Walton LR, Boustead NG, Carroll S, Wightman RM. Effects of Glutamate Receptor Activation on Local Oxygen Changes. ACS Chem Neurosci 2017; 8:1598-1608. [PMID: 28425701 PMCID: PMC5685152 DOI: 10.1021/acschemneuro.7b00088] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
![]()
Glutamate is ubiquitous
throughout the brain and serves as the
primary excitatory neurotransmitter. Neurons require energy to fire,
and energetic substrates (i.e., O2, glucose) are renewed
via cerebral blood flow (CBF) to maintain metabolic homeostasis. Magnetic
resonance brain functionality studies rely on the assumption that
CBF and neuronal activity are coupled consistently throughout the
brain; however, the origin of neuronal activity does not always coincide
with signals indicative of energy consumption (e.g., O2 decreases) at high spatial resolutions. Therefore, relationships
between excitatory neurotransmission and energy use must be evaluated
at higher resolutions. In this study, we showed that both endogenously
released and exogenously ejected glutamate decrease local tissue O2 concentrations, but whether hyperemic O2 restoration
followed depended on the stimulus method. Electrically stimulating
the glutamatergic corticostriatal pathway evoked biphasic O2 responses at striatal terminals: first O2 decreased,
then concentrations increased above baseline. Using iontophoresis
to locally eject ionotropic glutamate receptor antagonists revealed
that these receptors only influenced the O2 decrease. We
compared electrical stimulation to iontophoretic glutamate stimulation,
and measured concurrent single-unit activity and O2 to
limit both stimulation and recordings to <50 μm radius from
our sensor. Similarly, iontophoretic glutamate delivery elicited monophasic
O2 decreases without subsequent increases.
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Affiliation(s)
- Lindsay R. Walton
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Nick G. Boustead
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Susan Carroll
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - R. Mark Wightman
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
- Neuroscience Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
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111
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Schmid F, Barrett MJP, Jenny P, Weber B. Vascular density and distribution in neocortex. Neuroimage 2017; 197:792-805. [PMID: 28669910 DOI: 10.1016/j.neuroimage.2017.06.046] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Revised: 06/09/2017] [Accepted: 06/20/2017] [Indexed: 12/22/2022] Open
Abstract
An amazingly wide range of complex behavior emerges from the cerebral cortex. Much of the information processing that leads to these behaviors is performed in neocortical circuits that span throughout the six layers of the cortex. Maintaining this circuit activity requires substantial quantities of oxygen and energy substrates, which are delivered by the complex yet well-organized and tightly-regulated vascular system. In this review, we provide a detailed characterization of the most relevant anatomical and functional features of the cortical vasculature. This includes a compilation of the available data on laminar variation of vascular density and the topological aspects of the microvascular system. We also review the spatio-temporal dynamics of cortical blood flow regulation and oxygenation, many aspects of which remain poorly understood. Finally, we discuss some of the important implications of vascular density, distribution, oxygenation and blood flow regulation for (laminar) fMRI.
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Affiliation(s)
- Franca Schmid
- Institute of Fluid Dynamics, ETH Zurich, Sonneggstrasse 3, 8092, Zurich, Switzerland.
| | - Matthew J P Barrett
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland; Neuroscience Center, University and ETH Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
| | - Patrick Jenny
- Institute of Fluid Dynamics, ETH Zurich, Sonneggstrasse 3, 8092, Zurich, Switzerland
| | - Bruno Weber
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland; Neuroscience Center, University and ETH Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
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112
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Park HD, Bernasconi F, Salomon R, Tallon-Baudry C, Spinelli L, Seeck M, Schaller K, Blanke O. Neural Sources and Underlying Mechanisms of Neural Responses to Heartbeats, and their Role in Bodily Self-consciousness: An Intracranial EEG Study. Cereb Cortex 2017; 28:2351-2364. [DOI: 10.1093/cercor/bhx136] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 05/16/2017] [Indexed: 01/18/2023] Open
Affiliation(s)
- Hyeong-Dong Park
- Laboratory of Cognitive Neuroscience, Center for Neuroprosthetics and Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 9 Chemin des Mines, Geneva, Switzerland
| | - Fosco Bernasconi
- Laboratory of Cognitive Neuroscience, Center for Neuroprosthetics and Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 9 Chemin des Mines, Geneva, Switzerland
| | - Roy Salomon
- Gonda Multidisciplinary Brain Research Center, Bar Ilan University, Ramat Gan, Israel
| | - Catherine Tallon-Baudry
- Laboratoire de Neurosciences Cognitives (ENS – INSERM U960), Départment d’Etudes Cognitives, Ecole Normale Supérieure – PSL Research University, Paris, France
| | - Laurent Spinelli
- Presurgical Epilepsy Evaluation Unit, Department of Neurology, Geneva University Hospital (HUG), 4 Rue Gabrielle-Perret-Gentil, Geneva, Switzerland
| | - Margitta Seeck
- Presurgical Epilepsy Evaluation Unit, Department of Neurology, Geneva University Hospital (HUG), 4 Rue Gabrielle-Perret-Gentil, Geneva, Switzerland
| | - Karl Schaller
- Department of Neurosurgery, Geneva University Hospital (HUG), 4 Rue Gabrielle-Perret-Gentil, Geneva, Switzerland
| | - Olaf Blanke
- Laboratory of Cognitive Neuroscience, Center for Neuroprosthetics and Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), 9 Chemin des Mines, Geneva, Switzerland
- Department of Neurology, University of Geneva, 24 rue Micheli-du-Crest, Geneva, Switzerland
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113
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A proof-of-concept study for developing integrated two-photon microscopic and magnetic resonance imaging modality at ultrahigh field of 16.4 tesla. Sci Rep 2017; 7:2733. [PMID: 28578390 PMCID: PMC5457450 DOI: 10.1038/s41598-017-02864-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 04/19/2017] [Indexed: 11/09/2022] Open
Abstract
Functional magnetic resonance imaging (fMRI) based on the blood oxygen level dependent (BOLD) contrast has gained a prominent position in neuroscience for imaging neuronal activity and studying effective brain connectivity under working state and functional connectivity at resting state. However, the fundamental questions in regards to fMRI technology: how the BOLD signal inferences the underlying microscopic neuronal activity and physiological changes and what is the ultimate specificity of fMRI for functional mapping of microcircuits, remain unanswered. The capability of simultaneous fMRI measurement and functional microscopic imaging in a live brain thus holds the key to link the microscopic and mesoscopic neural dynamics to the macroscopic brain activity at the central nervous system level. Here we report the first demonstration to integrate high-resolution two-photon fluorescence microscopy (TPM) with a 16.4 tesla MRI system, which proves the concept and feasibility for performing simultaneous high-resolution fMRI and TPM imaging at ultrahigh magnetic field.
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114
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Lin L, Yao J, Zhang R, Chen CC, Huang CH, Li Y, Wang L, Chapman W, Zou J, Wang LV. High-speed photoacoustic microscopy of mouse cortical microhemodynamics. JOURNAL OF BIOPHOTONICS 2017; 10:792-798. [PMID: 28009098 PMCID: PMC5576888 DOI: 10.1002/jbio.201600236] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Revised: 11/28/2016] [Accepted: 12/07/2016] [Indexed: 05/03/2023]
Abstract
We applied high-speed photoacoustic microscopy (PAM) for both cortical microenvironment studies and dynamic brain studies, with micrometer-level optical resolution and a millisecond-level cross-sectional imaging speed over a millimeter-level field of view. We monitored blood flow redistribution in mini-stroke mouse models and cerebral autoregulation induced by a vasoactive agent. Our results collectively suggest that high-speed PAM is a promising tool for understanding dynamic neurophysiological phenomena, complementing conventional imaging modalities.
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Affiliation(s)
- Li Lin
- Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Junjie Yao
- Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Ruiying Zhang
- Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Chun-Cheng Chen
- Department of Surgery, Washington University School of Medicine, St. Louis, MO, USA
| | - Chih-Hsien Huang
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
| | - Yang Li
- Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Lidai Wang
- Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - William Chapman
- Department of Surgery, Washington University School of Medicine, St. Louis, MO, USA
| | - Jun Zou
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
- Correspondence: ,
| | - Lihong V. Wang
- Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
- Correspondence: ,
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115
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Liang XG, Chen B, Shao LX, Cheng J, Huang MZ, Chen Y, Hu YZ, Han YF, Han F, Li X. A Fluorogenic Probe for Ultrafast and Reversible Detection of Formaldehyde in Neurovascular Tissues. Am J Cancer Res 2017; 7:2305-2313. [PMID: 28740553 PMCID: PMC5505062 DOI: 10.7150/thno.19554] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 03/16/2017] [Indexed: 12/19/2022] Open
Abstract
Formaldehyde (FA) is endogenously produced in live systems and has been implicated in a diverse array of pathophysiological processes. To disentangle the detailed molecular mechanisms of FA biology, a reliable method for monitoring FA changes in live cells would be indispensable. Although there have been several fluorescent probes reported to detect FA, most are limited by the slow detection kinetics and the intrinsic disadvantage of detecting FA in an irreversible manner which may disturb endogenous FA homeostasis. Herein we developed a coumarin-hydrazonate based fluorogenic probe (PFM) based on a finely-tailored stereoelectronic effect. PFM could respond to FA swiftly and reversibly. This, together with its desirable specificity and sensitivity, endows us to track endogenous FA in live neurovascular cells with excellent temporal and spatial resolution. Further study in the brain tissue imaging showed the first direct observation of aberrant FA accumulation in cortex and hippocampus of Alzheimer's mouse model, indicating the potential of PFM as a diagnostic tool.
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Boussida S, Traoré AS, Durif F. Mapping of the brain hemodynamic responses to sensorimotor stimulation in a rodent model: A BOLD fMRI study. PLoS One 2017; 12:e0176512. [PMID: 28441420 PMCID: PMC5404844 DOI: 10.1371/journal.pone.0176512] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Accepted: 04/12/2017] [Indexed: 12/02/2022] Open
Abstract
Blood Oxygenation Level Dependent functional MRI (BOLD fMRI) during electrical paw stimulation has been widely used in studies aimed at the understanding of the somatosensory network in rats. However, despite the well-established anatomical connections between cortical and subcortical structures of the sensorimotor system, most of these functional studies have been concentrated on the cortical effects of sensory electrical stimulation. BOLD fMRI study of the integration of a sensorimotor input across the sensorimotor network requires an appropriate methodology to elicit functional activation in cortical and subcortical areas owing to the regional differences in both neuronal and vascular architectures between these brain regions. Here, using a combination of low level anesthesia, long pulse duration of the electrical stimulation along with improved spatial and temporal signal to noise ratios, we provide a functional description of the main cortical and subcortical structures of the sensorimotor rat brain. With this calibrated fMRI protocol, unilateral non-noxious sensorimotor electrical hindpaw stimulation resulted in robust positive activations in the contralateral sensorimotor cortex and bilaterally in the sensorimotor thalamus nuclei, whereas negative activations were observed bilaterally in the dorsolateral caudate-putamen. These results demonstrate that, once the experimental setup allowing necessary spatial and temporal signal to noise ratios is reached, hemodynamic changes related to neuronal activity, as preserved by the combination of a soft anesthesia with a soft muscle relaxation, can be measured within the sensorimotor network. Moreover, the observed responses suggest that increasing pulse duration of the electrical stimulus adds a proprioceptive component to the sensory input that activates sensorimotor network in the brain, and that these activation patterns are similar to those induced by digits paw’s movements. These findings may find application in fMRI studies of sensorimotor disorders within cortico-basal network in rodents.
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Abe Y, Tsurugizawa T, Le Bihan D. Water diffusion closely reveals neural activity status in rat brain loci affected by anesthesia. PLoS Biol 2017; 15:e2001494. [PMID: 28406906 PMCID: PMC5390968 DOI: 10.1371/journal.pbio.2001494] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Accepted: 03/16/2017] [Indexed: 11/18/2022] Open
Abstract
Diffusion functional MRI (DfMRI) reveals neuronal activation even when neurovascular coupling is abolished, contrary to blood oxygenation level—dependent (BOLD) functional MRI (fMRI). Here, we show that the water apparent diffusion coefficient (ADC) derived from DfMRI increased in specific rat brain regions under anesthetic conditions, reflecting the decreased neuronal activity observed with local field potentials (LFPs), especially in regions involved in wakefulness. In contrast, BOLD signals showed nonspecific changes, reflecting systemic effects of the anesthesia on overall brain hemodynamics status. Electrical stimulation of the central medial thalamus nucleus (CM) exhibiting this anesthesia-induced ADC increase led the animals to transiently wake up. Infusion in the CM of furosemide, a specific neuronal swelling blocker, led the ADC to increase further locally, although LFP activity remained unchanged, and increased the current threshold awakening the animals under CM electrical stimulation. Oppositely, induction of cell swelling in the CM through infusion of a hypotonic solution (−80 milliosmole [mOsm] artificial cerebrospinal fluid [aCSF]) led to a local ADC decrease and a lower current threshold to wake up the animals. Strikingly, the local ADC changes produced by blocking or enhancing cell swelling in the CM were also mirrored remotely in areas functionally connected to the CM, such as the cingulate and somatosensory cortex. Together, those results strongly suggest that neuronal swelling is a significant mechanism underlying DfMRI. It has been reported that neuronal activation results in a decrease of water diffusion in activated neural tissue. This new approach, known as diffusion functional MRI (DfMRI), has high potential for functional imaging of the brain, as the currently widespread blood oxygenation level—dependent (BOLD)-functional MRI (fMRI) method, which is based on neurovascular coupling, remains an indirect marker of neuronal activation. Here, we show that the water apparent diffusion coefficient (ADC) derived from DfMRI increased in specific rat brain regions under anesthetic conditions, reflecting the decreased neuronal activity, especially in regions involved in wakefulness. Electrical stimulation of the central medial (CM) thalamic nucleus exhibiting this anesthesia-induced ADC increase led the animals to transiently wake up. Infusion of the CM with furosemide—a specific blocker of neuronal swelling—led the ADC to increase further locally and increased the current threshold for waking the animals. Conversely, induction of cell swelling in the CM through infusion of a hypotonic solution led to a local ADC decrease and a lower current threshold to wake the animals. Strikingly, the local ADC changes produced by blocking or enhancing cell swelling in the CM were also mirrored remotely in areas functionally connected to the CM, such as the cingulate and somatosensory cortex. Those results strongly suggest that neuronal swelling is a significant mechanism underlying DfMRI.
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Affiliation(s)
- Yoshifumi Abe
- NeuroSpin, Joliot Institute, Commissariat à l'énergie atomique et aux énergies alternatives, Gif-sur-Yvette, France
| | - Tomokazu Tsurugizawa
- NeuroSpin, Joliot Institute, Commissariat à l'énergie atomique et aux énergies alternatives, Gif-sur-Yvette, France
| | - Denis Le Bihan
- NeuroSpin, Joliot Institute, Commissariat à l'énergie atomique et aux énergies alternatives, Gif-sur-Yvette, France
- * E-mail:
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De Martino F, Yacoub E, Kemper V, Moerel M, Uludağ K, De Weerd P, Ugurbil K, Goebel R, Formisano E. The impact of ultra-high field MRI on cognitive and computational neuroimaging. Neuroimage 2017; 168:366-382. [PMID: 28396293 DOI: 10.1016/j.neuroimage.2017.03.060] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Revised: 03/20/2017] [Accepted: 03/29/2017] [Indexed: 01/14/2023] Open
Abstract
The ability to measure functional brain responses non-invasively with ultra high field MRI (7 T and above) represents a unique opportunity in advancing our understanding of the human brain. Compared to lower fields (3 T and below), ultra high field MRI has an increased sensitivity, which can be used to acquire functional images with greater spatial resolution, and greater specificity of the blood oxygen level dependent (BOLD) signal to the underlying neuronal responses. Together, increased resolution and specificity enable investigating brain functions at a submillimeter scale, which so far could only be done with invasive techniques. At this mesoscopic spatial scale, perception, cognition and behavior can be probed at the level of fundamental units of neural computations, such as cortical columns, cortical layers, and subcortical nuclei. This represents a unique and distinctive advantage that differentiates ultra high from lower field imaging and that can foster a tighter link between fMRI and computational modeling of neural networks. So far, functional brain mapping at submillimeter scale has focused on the processing of sensory information and on well-known systems for which extensive information is available from invasive recordings in animals. It remains an open challenge to extend this methodology to uniquely human functions and, more generally, to systems for which animal models may be problematic. To succeed, the possibility to acquire high-resolution functional data with large spatial coverage, the availability of computational models of neural processing as well as accurate biophysical modeling of neurovascular coupling at mesoscopic scale all appear necessary.
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Affiliation(s)
- Federico De Martino
- Department of Cognitive Neurosciences, Faculty of Psychology and Neuroscience, Maastricht University, Oxfordlaan 55, 6229 ER Maastricht, The Netherlands; Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, 2021 sixth street SE, 55455 Minneapolis, MN, USA.
| | - Essa Yacoub
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, 2021 sixth street SE, 55455 Minneapolis, MN, USA
| | - Valentin Kemper
- Department of Cognitive Neurosciences, Faculty of Psychology and Neuroscience, Maastricht University, Oxfordlaan 55, 6229 ER Maastricht, The Netherlands
| | - Michelle Moerel
- Department of Cognitive Neurosciences, Faculty of Psychology and Neuroscience, Maastricht University, Oxfordlaan 55, 6229 ER Maastricht, The Netherlands; Maastricht Center for System Biology, Maastricht University, Universiteitssingel 60, 6229 ER Maastricht, The Netherlands
| | - Kâmil Uludağ
- Department of Cognitive Neurosciences, Faculty of Psychology and Neuroscience, Maastricht University, Oxfordlaan 55, 6229 ER Maastricht, The Netherlands
| | - Peter De Weerd
- Department of Cognitive Neurosciences, Faculty of Psychology and Neuroscience, Maastricht University, Oxfordlaan 55, 6229 ER Maastricht, The Netherlands
| | - Kamil Ugurbil
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, 2021 sixth street SE, 55455 Minneapolis, MN, USA
| | - Rainer Goebel
- Department of Cognitive Neurosciences, Faculty of Psychology and Neuroscience, Maastricht University, Oxfordlaan 55, 6229 ER Maastricht, The Netherlands
| | - Elia Formisano
- Department of Cognitive Neurosciences, Faculty of Psychology and Neuroscience, Maastricht University, Oxfordlaan 55, 6229 ER Maastricht, The Netherlands; Maastricht Center for System Biology, Maastricht University, Universiteitssingel 60, 6229 ER Maastricht, The Netherlands
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119
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Sclocco R, Beissner F, Bianciardi M, Polimeni JR, Napadow V. Challenges and opportunities for brainstem neuroimaging with ultrahigh field MRI. Neuroimage 2017; 168:412-426. [PMID: 28232189 DOI: 10.1016/j.neuroimage.2017.02.052] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Revised: 01/30/2017] [Accepted: 02/19/2017] [Indexed: 12/19/2022] Open
Abstract
The human brainstem plays a central role in connecting the cerebrum, the cerebellum and the spinal cord to one another, hosting relay nuclei for afferent and efferent signaling, and providing source nuclei for several neuromodulatory systems that impact central nervous system function. While the investigation of the brainstem with functional or structural magnetic resonance imaging has been hampered for years due to this brain structure's physiological and anatomical characteristics, the field has seen significant advances in recent years thanks to the broader adoption of ultrahigh-field (UHF) MRI scanning. In the present review, we focus on the advantages offered by UHF in the context of brainstem imaging, as well as the challenges posed by the investigation of this complex brain structure in terms of data acquisition and analysis. We also illustrate how UHF MRI can shed new light on the neuroanatomy and neurophysiology underlying different brainstem-based circuitries, such as the central autonomic network and neurotransmitter/neuromodulator systems, discuss existing and foreseeable clinical applications to better understand diseases such as chronic pain and Parkinson's disease, and explore promising future directions for further improvements in brainstem imaging using UHF MRI techniques.
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Affiliation(s)
- Roberta Sclocco
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, CNY 149-2301, 13th St. Charlestown, Boston, MA 02129, USA; Department of Radiology, Logan University, Chesterfield, MO, USA.
| | - Florian Beissner
- Somatosensory and Autonomic Therapy Research, Institute for Neuroradiology, Hannover Medical School, Hannover, Germany
| | - Marta Bianciardi
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, CNY 149-2301, 13th St. Charlestown, Boston, MA 02129, USA
| | - Jonathan R Polimeni
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, CNY 149-2301, 13th St. Charlestown, Boston, MA 02129, USA; Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Vitaly Napadow
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, CNY 149-2301, 13th St. Charlestown, Boston, MA 02129, USA; Department of Radiology, Logan University, Chesterfield, MO, USA
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120
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Hu X, De Silva TM, Chen J, Faraci FM. Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke. Circ Res 2017; 120:449-471. [PMID: 28154097 PMCID: PMC5313039 DOI: 10.1161/circresaha.116.308427] [Citation(s) in RCA: 256] [Impact Index Per Article: 36.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Revised: 10/13/2016] [Accepted: 10/26/2016] [Indexed: 12/13/2022]
Abstract
The consequences of cerebrovascular disease are among the leading health issues worldwide. Large and small cerebral vessel disease can trigger stroke and contribute to the vascular component of other forms of neurological dysfunction and degeneration. Both forms of vascular disease are driven by diverse risk factors, with hypertension as the leading contributor. Despite the importance of neurovascular disease and subsequent injury after ischemic events, fundamental knowledge in these areas lag behind our current understanding of neuroprotection and vascular biology in general. The goal of this review is to address select key structural and functional changes in the vasculature that promote hypoperfusion and ischemia, while also affecting the extent of injury and effectiveness of therapy. In addition, as damage to the blood-brain barrier is one of the major consequences of ischemia, we discuss cellular and molecular mechanisms underlying ischemia-induced changes in blood-brain barrier integrity and function, including alterations in endothelial cells and the contribution of pericytes, immune cells, and matrix metalloproteinases. Identification of cell types, pathways, and molecules that control vascular changes before and after ischemia may result in novel approaches to slow the progression of cerebrovascular disease and lessen both the frequency and impact of ischemic events.
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Affiliation(s)
- Xiaoming Hu
- Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - T. Michael De Silva
- Biomedicine Discovery Institute, Department of Pharmacology, 9 Ancora Imparo Way, Monash University, Clayton, Vic, Australia
| | - Jun Chen
- Center of Cerebrovascular Disease Research, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Frank M. Faraci
- Departments of Internal Medicine and Pharmacology, Carver College of Medicine, University of Iowa, Iowa City Veterans Affairs Healthcare System, Iowa City, IA, USA
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121
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Guest O, Love BC. What the success of brain imaging implies about the neural code. eLife 2017; 6. [PMID: 28103186 PMCID: PMC5245971 DOI: 10.7554/elife.21397] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Accepted: 12/23/2016] [Indexed: 12/05/2022] Open
Abstract
The success of fMRI places constraints on the nature of the neural code. The fact that researchers can infer similarities between neural representations, despite fMRI’s limitations, implies that certain neural coding schemes are more likely than others. For fMRI to succeed given its low temporal and spatial resolution, the neural code must be smooth at the voxel and functional level such that similar stimuli engender similar internal representations. Through proof and simulation, we determine which coding schemes are plausible given both fMRI’s successes and its limitations in measuring neural activity. Deep neural network approaches, which have been forwarded as computational accounts of the ventral stream, are consistent with the success of fMRI, though functional smoothness breaks down in the later network layers. These results have implications for the nature of the neural code and ventral stream, as well as what can be successfully investigated with fMRI. DOI:http://dx.doi.org/10.7554/eLife.21397.001 We can appreciate that a cat is more similar to a dog than to a truck. The combined activity of millions of neurons in the brain somehow captures these everyday similarities, and this activity can be measured using imaging techniques such as functional magnetic resonance imaging (fMRI). However, fMRI scanners are not particularly precise – they average together the responses of many thousands of neurons over several seconds, which provides a blurry snapshot of brain activity. Nevertheless, the pattern of activity measured when viewing a photograph of a cat is more similar to that seen when viewing a picture of a dog than a picture of a truck. This tells us a lot about how the brain codes information, as only certain coding methods would allow fMRI to capture these similarities given the technique’s limitations. There are many different models that attempt to describe how the brain codes similarity relations. Some models use the principle of neural networks, in which neurons can be considered as arranged into interconnected layers. In such models, neurons transmit information from one layer to the next. By investigating which models are consistent with fMRI’s ability to capture similarity relations, Guest and Love have found that certain neural network models are plausible accounts of how the brain represents and processes information. These models include the deep learning networks that contain many layers of neurons and are popularly used in artificial intelligence. Other modeling approaches do not account for the ability of fMRI to capture similarity relations. As neural networks become deeper with more layers, they should be less readily understood using fMRI: as the number of layers increases, the representations of objects with similarities (for example, cats and dogs) become more unrelated. One question that requires further investigation is whether this finding explains why certain parts of the brain are more difficult to image. DOI:http://dx.doi.org/10.7554/eLife.21397.002
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Affiliation(s)
- Olivia Guest
- Experimental Psychology, University College London, London, United Kingdom
| | - Bradley C Love
- Experimental Psychology, University College London, London, United Kingdom.,The Alan Turing Institute, London, United Kingdom
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122
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Ma Z, Cao P, Sun P, Lu Z, Li L, Chen Y, Chai X. Negative hemodynamic response without neuronal inhibition investigated by combining optical imaging and electrophysiological recording. Neurosci Lett 2017; 637:161-167. [DOI: 10.1016/j.neulet.2016.11.029] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Revised: 11/06/2016] [Accepted: 11/12/2016] [Indexed: 12/26/2022]
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123
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Rungta RL, Charpak S. Astrocyte endfeet march to the beat of different vessels. Nat Neurosci 2016; 19:1539-1541. [PMID: 27898083 DOI: 10.1038/nn.4446] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Ravi L Rungta
- INSERM U1128, Laboratory of Neurophysiology and New Microscopy, Université Paris Descartes, Paris, France
| | - Serge Charpak
- INSERM U1128, Laboratory of Neurophysiology and New Microscopy, Université Paris Descartes, Paris, France
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124
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Abstract
Oscillatory neural dynamics play an important role in the coordination of large-scale brain networks. High-level cognitive processes depend on dynamics evolving over hundreds of milliseconds, so measuring neural activity in this frequency range is important for cognitive neuroscience. However, current noninvasive neuroimaging methods are not able to precisely localize oscillatory neural activity above 0.2 Hz. Electroencephalography and magnetoencephalography have limited spatial resolution, whereas fMRI has limited temporal resolution because it measures vascular responses rather than directly recording neural activity. We hypothesized that the recent development of fast fMRI techniques, combined with the extra sensitivity afforded by ultra-high-field systems, could enable precise localization of neural oscillations. We tested whether fMRI can detect neural oscillations using human visual cortex as a model system. We detected small oscillatory fMRI signals in response to stimuli oscillating at up to 0.75 Hz within single scan sessions, and these responses were an order of magnitude larger than predicted by canonical linear models. Simultaneous EEG-fMRI and simulations based on a biophysical model of the hemodynamic response to neuronal activity suggested that the blood oxygen level-dependent response becomes faster for rapidly varying stimuli, enabling the detection of higher frequencies than expected. Accounting for phase delays across voxels further improved detection, demonstrating that identifying vascular delays will be of increasing importance with higher-frequency activity. These results challenge the assumption that the hemodynamic response is slow, and demonstrate that fMRI has the potential to map neural oscillations directly throughout the brain.
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125
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Serences JT. Neural mechanisms of information storage in visual short-term memory. Vision Res 2016; 128:53-67. [PMID: 27668990 DOI: 10.1016/j.visres.2016.09.010] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Revised: 09/02/2016] [Accepted: 09/21/2016] [Indexed: 11/26/2022]
Abstract
The capacity to briefly memorize fleeting sensory information supports visual search and behavioral interactions with relevant stimuli in the environment. Traditionally, studies investigating the neural basis of visual short term memory (STM) have focused on the role of prefrontal cortex (PFC) in exerting executive control over what information is stored and how it is adaptively used to guide behavior. However, the neural substrates that support the actual storage of content-specific information in STM are more controversial, with some attributing this function to PFC and others to the specialized areas of early visual cortex that initially encode incoming sensory stimuli. In contrast to these traditional views, I will review evidence suggesting that content-specific information can be flexibly maintained in areas across the cortical hierarchy ranging from early visual cortex to PFC. While the factors that determine exactly where content-specific information is represented are not yet entirely clear, recognizing the importance of task-demands and better understanding the operation of non-spiking neural codes may help to constrain new theories about how memories are maintained at different resolutions, across different timescales, and in the presence of distracting information.
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Affiliation(s)
- John T Serences
- Department of Psychology, Neurosciences Graduate Program, and the Kavli Institute for Mind and Brain, University of California, San Diego, United States.
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126
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Aksenov DP, Li L, Miller MJ, Wyrwicz AM. Blood oxygenation level dependent signal and neuronal adaptation to optogenetic and sensory stimulation in somatosensory cortex in awake animals. Eur J Neurosci 2016; 44:2722-2729. [PMID: 27564781 DOI: 10.1111/ejn.13384] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Revised: 08/18/2016] [Accepted: 08/23/2016] [Indexed: 11/27/2022]
Abstract
The adaptation of neuronal responses to stimulation, in which a peak transient response is followed by a sustained plateau, has been well-studied. The blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal has also been shown to exhibit adaptation on a longer time scale. However, some regions such as the visual and auditory cortices exhibit significant BOLD adaptation, whereas other such as the whisker barrel cortex may not adapt. In the sensory cortex a combination of thalamic inputs and intracortical activity drives hemodynamic changes, although the relative contributions of these components are not entirely understood. The aim of this study is to assess the role of thalamic inputs vs. intracortical processing in shaping BOLD adaptation during stimulation in the somatosensory cortex. Using simultaneous fMRI and electrophysiology in awake rabbits, we measured BOLD, local field potentials (LFPs), single- and multi-unit activity in the cortex during whisker and optogenetic stimulation. This design allowed us to compare BOLD and haemodynamic responses during activation of the normal thalamocortical sensory pathway (i.e., both inputs and intracortical activity) vs. the direct optical activation of intracortical circuitry alone. Our findings show that whereas LFP and multi-unit (MUA) responses adapted, neither optogenetic nor sensory stimulation produced significant BOLD adaptation. We observed for both paradigms a variety of excitatory and inhibitory single unit responses. We conclude that sensory feed-forward thalamic inputs are not primarily responsible for shaping BOLD adaptation to stimuli; but the single-unit results point to a role in this behaviour for specific excitatory and inhibitory neuronal sub-populations, which may not correlate with aggregate neuronal activity.
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Affiliation(s)
- Daniil P Aksenov
- NorthShore University HealthSystem, 1033 University Pl., Suite 100, Evanston, IL, 60201, USA
| | - Limin Li
- NorthShore University HealthSystem, 1033 University Pl., Suite 100, Evanston, IL, 60201, USA
| | - Michael J Miller
- NorthShore University HealthSystem, 1033 University Pl., Suite 100, Evanston, IL, 60201, USA
| | - Alice M Wyrwicz
- NorthShore University HealthSystem, 1033 University Pl., Suite 100, Evanston, IL, 60201, USA.
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127
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Shackman AJ, Fox AS. Contributions of the Central Extended Amygdala to Fear and Anxiety. J Neurosci 2016; 36:8050-63. [PMID: 27488625 PMCID: PMC4971357 DOI: 10.1523/jneurosci.0982-16.2016] [Citation(s) in RCA: 184] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2016] [Revised: 05/30/2016] [Accepted: 06/03/2016] [Indexed: 01/01/2023] Open
Abstract
It is widely thought that phasic and sustained responses to threat reflect dissociable circuits centered on the central nucleus of the amygdala (Ce) and the bed nucleus of the stria terminalis (BST), the two major subdivisions of the central extended amygdala. Early versions of this hypothesis remain highly influential and have been incorporated into the National Institute of Mental Health Research Research Domain Criteria framework. However, new observations encourage a different perspective. Anatomical studies show that the Ce and BST form a tightly interconnected unit, where different kinds of threat-relevant information can be integrated and used to assemble states of fear and anxiety. Imaging studies in humans and monkeys show that the Ce and BST exhibit similar functional profiles. Both regions are sensitive to a range of aversive challenges, including uncertain or temporally remote threat; both covary with concurrent signs and symptoms of fear and anxiety; both show phasic responses to short-lived threat; and both show heightened activity during sustained exposure to diffusely threatening contexts. Mechanistic studies demonstrate that both regions can control the expression of fear and anxiety during sustained exposure to diffuse threat. These observations compel a reconsideration of the central extended amygdala's contributions to fear and anxiety and its role in neuropsychiatric disease.
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Affiliation(s)
- Alexander J Shackman
- Department of Psychology, Neuroscience and Cognitive Science Program, and Maryland Neuroimaging Center, University of Maryland, College Park, Maryland 20742, and
| | - Andrew S Fox
- Department of Psychology and California National Primate Research Center, University of California, Davis, California 95616
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128
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Going with the flow. Nat Rev Neurosci 2016; 17:400. [DOI: 10.1038/nrn.2016.83] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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