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| Afonso C. Silva, Ph.D., Investigator |
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Dr. Silva received his Bachelor's Degree in Electrical Engineering from Universidade Federal de Pernambuco in Recife, Brazil, and his Ph.D. in Bioengineering from Carnegie Mellon University, where he worked on non-invasive MRI measurements of cerebral blood flow using the arterial spin labeling technique. He then went on to do post-doctoral training in the Center for Magnetic Resonance Research at the University of Minnesota, where he studied the temporal and spatial characteristics of functional brain hemodynamics under the supervision of Prof. Seong-Gi Kim. Dr. Silva joined NINDS as a Staff Scientist in 1999, and became an investigator in 2004. His laboratory combines modern neuroimaging techniques (functional MRI, and optical imaging) with electrophysiological recordings aimed at understanding the mechanisms of regulation of cerebral blood flow during normal and stimulation-induced brain activity.
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Staff:
- Dr. Nicholas A Bock, Ph.D., Postdoctoral Fellow, (301) 402-2432 BockN@ninds.nih.gov
- Dr. George Carlos do Nascimento, Ph.D., Research Fellow, (301) 451-1873 NascimeG@ninds.nih.gov
- Mr. Fernando Fernandes Paiva, M.S., Pre-doctoral IRTA, (301) 594-3031 PaivaF@ninds.nih.gov
- Ms. Sachy E. Sato, Contractor, (301) 402-1457 SatoS@mail.nih.gov
- Dr. Bojana Stefanovic, Ph.D., Postdoctoral Fellow, (301) 402-3753 StefanovicB@ninds.nih.gov
Research Interests:
Modern functional neuroimaging methods, such as Positron Emission Tomography (PET), and functional Magnetic Resonance Imaging (fMRI), rely on the coupling of neuronal electrical activity to changes in local metabolic demands - the "cerebrometabolic coupling" - to the hemodynamic regulation of energy supply and waste removal - the "cerebrovascular coupling" -to measure brain activity through indirect surrogate markers. The first reported observations of hemodynamic changes associated with local brain activity where made over 100 years ago, and yet fundamental questions still remain about the spatial localization of cerebral blood flow changes with respect to the site of neural activity, the specific signaling pathways that cause vasodilatation, and the mechanisms that restore the vasculature to a normal state after normalization of brain activity.
Such mechanisms form the basis of support of any and all brain activity, and our main research interests are to understand and to elucidate cerebral blood flow regulation during normal and stimulation induced brain activity. The fundamental questions related to cerebral blood flow regulation are:
1. What is the smallest vascular unit that adapts independently to brain activity?
2. How is this elemental vascular unit related to the cortical architecture?
3. What are the major signaling pathways, and the key molecules, that translate a change in brain activity into a vascular response?
To address the above questions, we are working on well-defined rodent and non-human primate models of localized functional brain activation, using modern neuroimaging techniques (fMRI or optical microscopy), in combination with electrophysiology recordings of cortical activity. The cerebrovascular coupling will be tested under the presence of agonists and antagonists of several different known mediators or modulators of CBF. Complimentary information on the cerebrovascular coupling will be studied under pathophysiological brain conditions, such as the ones obtained using experimental animal models of brain stroke. LFMI website http://www.lfmi.ninds.nih.gov/
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Selected Recent Publications:
S. D. Keilholz, A. C. Silva, M. Raman, H. Merkle, A. P. Koretsky (2006) BOLD and CBV-Weighted Functional Magnetic Resonance Imaging of the Rat Somatosensory System, Magnetic Resonance in Medicine 55(2), 316–324.
Full Text/Abstract
I. Aoki, Y. Takahashi, K.-H. Chuang, A. C. Silva, T. Igarashi, C. Tanaka, R. W. Childs, A. P. Koretsky (2006) Cell labeling for magnetic resonance imaging with the T1 agent manganese chloride, NMR in Biomedicine 19(1), 50-59.
Full Text/Abstract
J. H. Lee, A. C. Silva, H. Merkle, A. P. Koretsky (2005) Manganese-enhanced magnetic resonance imaging of mouse brain after systemic administration of MnCl2: dose-dependent and temporal evolution of T1 contrast, Magnetic Resonance in Medicine 53(3), 640-648.
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J. A. de Zwart, A. C. Silva, P. van Gelderen, P. Kellman, M. Fukunaga, R. Chu, A. P. Koretsky, J. A. Frank, J. H. Duyn (2005) Temporal dynamics of the BOLD fMRI impulse response, Neuroimage 24(3), 667-677.
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Chen Z, Silva AC, Yang J, Shen J. (2005) Elevated endogenous GABA level correlates with decreased fMRI signals in the rat brain during acute inhibition of GABA transaminase, J Neurosci Res. 79(3), 383-391.
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A. C. Silva (2005) Perfusion-based fMRI: insights from animal models, Journal of Magnetic Resonance Imaging 22(6), 745-750.
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S. Keilholz, A. C. Silva, M. Raman, H. Merkle, and A. P. Koretsky (2004) Functional MRI of the Rodent Somatosensory Pathway Using Multi-slice Echo Planar Imaging, Magn. Reson. Med 52(1), 89-99.
Full Text/Abstract
All Selected Publications
Contact Information:
Dr. Afonso C. Silva
Cerebral Microcirculation Unit
Laboratory of Functional and Molecular Imaging, NINDS
NIH, Building 10, Room B1D106
10 Center Drive, MSC 1065
Bethesda, MD 20892-1065
Telephone: (301) 402-9703 (office),
(301) 480-2558 (fax)
Email: SilvaA@ninds.nih.gov
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