Papers by Siddheshvarananda Avt
Annual Review of Neuroscience, 1990
Proceedings of The National Academy of Sciences, 1992
Neuronal activity causes local changes in cerebral blood flow, blood volume, and blood oxygenatio... more Neuronal activity causes local changes in cerebral blood flow, blood volume, and blood oxygenation. Magnetic resonance imaging (MRI) techniques sensitive to changes in cerebral blood flow and blood oxygenation were developed by high-speed echo planar imaging. These techniques were used to obtain completely noninvasive tomographic maps of human brain activity, by using visual and motor stimulus paradigms. Changes in blood oxygenation were detected by using a gradient echo (GE) imaging sequence sensitive to the paramagnetic state of deoxygenated hemoglobin. Blood flow changes were evaluated by a spin-echo inversion recovery (IR), tissue relaxation parameter Tl-sensitive pulse sequence. A series of images were acquired continuously with the same imaging pulse sequence (either GE or IR) during task activation. Cine display of subtraction images (activated minus baseline) directly demonstrates activity-induced changes in brain MR signal observed at a temporal resolution of seconds. During 8-Hz patterned-flash photic stimulation, a significant increase in signal intensity (paired t test; P < 0.001) of 1.8% ± 0.8% (GE) and 1.8% ± 0.9% (ID) was observed in the primary visual cortex (Vi) of seven normal volunteers. The mean rise-time constant of the signal change was 4.4 ± 2.2 s for the GE images and 8.9 ± 2.8 s for the IR images. The stimulation frequency dependence of visual activation agrees with previous positron emission tomography observations, with the largest MR signal response occurring at 8 Hz. Similar signal changes were observed within the human primary motor cortex (Ml) during a hand squeezing task and in animal models of increased blood flow by hypercapnia. By using intrinsic blood-tissue contrast, functional MRI opens a spatialtemporal window onto individual brain physiology.
IEEE Journal on Selected Areas in Communications, 2005
... At the other end of the scale, the user may employ multiple implementation technologies to bu... more ... At the other end of the scale, the user may employ multiple implementation technologies to build its cognitive cycle around a wideband spectrum hole or set of narrowband spectrum holes to provide the best expected performance in terms of spectrum management and transmit ...
Brain, 1952
INTRODUCTION THE earliest references to spondylitis as a cause of paraplegia appear to be those o... more INTRODUCTION THE earliest references to spondylitis as a cause of paraplegia appear to be those of Strumpell (1888), Marie (1898) and von Bechterew (1899). Horsley in 1892 (Taylor and Collier, 1901) successfully operated on what appears to have been a case of traumatic ...
Educação e pesquisa, 2000
... Assim sen do, tra ba lhei com par te da pro du ção da Fa cul da de de Me di ci na do Rio de J... more ... Assim sen do, tra ba lhei com par te da pro du ção da Fa cul da de de Me di ci na do Rio de Ja ne i ro (FMRJ), so bre tu do com as te ses de ... Lon de, Ros - tan, Tar di eu, Levy e ou tros são os re pre sen tan - tes da hygi e ne ac tu al, a qual se ain da não che gou ao seu ma i or ...
... sound design were by David Van Tieghem; the production stage manager was Renee Lutz; and the ... more ... sound design were by David Van Tieghem; the production stage manager was Renee Lutz; and the assistant stage manager was Tammy Scozzafava. ... A pair of sandals, one shawl, and a thousand dollars worth of Moroccan leather suitcases that&#x27;ve never even been opened, I ...
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Papers by Siddheshvarananda Avt