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BOLD Data (bold + data)
Selected AbstractsComparison of spatial integration and surround suppression characteristics in spiking activity and the local field potential in macaque V1EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2008M. A. Gieselmann Abstract Neurons in primary visual cortex exhibit well documented centre,surround receptive field organization, whereby the centre is dominated by excitatory influences and the surround is generally dominated by inhibitory influences. These effects have largely been established by measuring the output of neurons, i.e. their spiking activity. How excitation and inhibition are reflected in the local field potential (LFP) is little understood. As this can bear on the interpretation of human fMRI BOLD data and on our understanding of the mechanisms of local field potential oscillations, we measured spatial integration and centre,surround properties in single- and multiunit recordings of V1 in the awake fixating macaque monkey, and compared these to spectral power in different frequency bands of simultaneously recorded LFPs. We quantified centre,surround organization by determining the size of the summation and suppression area in spiking activity as well as in different frequency bands of the LFP, with the main focus on the gamma band. Gratings extending beyond the summation area usually inhibited spiking activity while the LFP gamma-band activity increased monotonically for all grating sizes. This increase was maximal for stimuli infringing upon the near classical receptive field surround, where suppression started to dominate spiking activity. Thus, suppressive influences in primary cortex can be inferred from spiking activity, but they also seem to affect specific features of gamma-band LFP activity. [source] Functional segmentation of the brain cortex using high model order group PICAHUMAN BRAIN MAPPING, Issue 12 2009Vesa Kiviniemi Abstract Baseline activity of resting state brain networks (RSN) in a resting subject has become one of the fastest growing research topics in neuroimaging. It has been shown that up to 12 RSNs can be differentiated using an independent component analysis (ICA) of the blood oxygen level dependent (BOLD) resting state data. In this study, we investigate how many RSN signal sources can be separated from the entire brain cortex using high dimension ICA analysis from a group dataset. Group data from 55 subjects was analyzed using temporal concatenation and a probabilistic independent component analysis algorithm. ICA repeatability testing verified that 60 of the 70 computed components were robustly detectable. Forty-two independent signal sources were identifiable as RSN, and 28 were related to artifacts or other noninterest sources (non-RSN). The depicted RSNs bore a closer match to functional neuroanatomy than the previously reported RSN components. The non-RSN sources have significantly lower temporal intersource connectivity than the RSN (P < 0.0003). We conclude that the high model order ICA of the group BOLD data enables functional segmentation of the brain cortex. The method enables new approaches to causality and connectivity analysis with more specific anatomical details. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] Imaging brain activity during natural vision using CASL perfusion fMRIHUMAN BRAIN MAPPING, Issue 7 2007Hengyi Rao Abstract Functional MRI (fMRI) has begun to be used to explore human brain activity during ecological and natural conditions. Arterial spin labeling (ASL) perfusion fMRI provides an appealing approach for imaging sustained brain activity during natural conditions because of its long-term temporal stability and ability to noninvasively quantify absolute cerebral blood flow (CBF). The present study used ASL perfusion fMRI to measure brain activation patterns associated with natural vision by concurrently recording CBF and blood oxygen level-dependent (BOLD) contrasts while subjects were freely viewing a cartoon movie. Reliable quantitative whole-brain CBF values (,60 mL/100g/min) as well as regional CBF values (45,80 mL/100g/min) were measured during movie viewing and resting states. The perfusion contrast revealed CBF increases in multiple visual pathway areas and frontal areas, and CBF decreases in ventromedial frontal cortex and superior temporal cortex during movie viewing compared to resting states. Concurrent BOLD contrast revealed similar but weaker activation and deactivation patterns. Regression analyses of both CBF data and BOLD data showed significant associations between activation in the middle temporal (MT) region and subjects' perception of motion. Region of interest analysis based on a priori literature-defined MT demonstrated significant monotonic stepwise associations between the intensity of motion perception and the CBF and BOLD signal changes. These results demonstrate the feasibility of using ASL perfusion fMRI for imaging both sustained and dynamic effects in neural activation during natural and ecologically valid situations, and support the notion of maintained functional segregation and specialization during natural vision. Hum Brain Mapp, 2006. © 2006 Wiley-Liss, Inc. [source] Assessment of regional myocardial oxygenation changes in the presence of coronary artery stenosis with balanced SSFP imaging at 3.0T: Theory and experimental evaluation in caninesJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2008Rohan Dharmakumar PhD Abstract Purpose To examine the dependence of steady-state free-precession (SSFP) -based myocardial blood-oxygen-level-dependent (BOLD) contrast on field strength using theoretical and experimental models. Materials and Methods Numerical simulations using a two-pool exchange model and a surgically prepared dog model were used to assess the SSFP-based myocardial BOLD signal changes at 1.5T and 3.0T. Experimental studies were performed in eight canines with pharmacological vasodilation under various levels of left circumflex coronary artery stenosis. Experimentally obtained BOLD signal changes were correlated against microsphere-based true flow changes. Results Theoretical results showed that, at 3.0T, relative to 1.5T, a threefold increase in oxygen sensitivity can be expected. Experimental studies in canines showed near similar results,a 2.5 ± 0.2-fold increase in BOLD sensitivity at 3.0T relative to 1.5T (P < 0.05). Based on the scatter gram of BOLD data and microsphere data, it was found that the minimum regional flow difference that can be detected with SSFP-based myocardial BOLD imaging at 1.5T and 3.0T were 2.9 and 1.6, respectively (P < 0.05). Conclusion This study demonstrated that SSFP-based myocardial BOLD sensitivity is substantially greater at 3.0T compared with 1.5T. The findings here suggest that SSFP-based myocardial BOLD imaging at 3.0T may have the necessary sensitivity to detect the clinically required minimum flow difference of 2.0. J. Magn. Reson. Imaging 2008;27:1037,1045. © 2008 Wiley-Liss, Inc. [source] Stimulation of the rat somatosensory cortex at different frequencies and pulse widthsNMR IN BIOMEDICINE, Issue 1 2006N. Van Camp Abstract Functional MRI (fMRI) during electrical somatosensory stimulation of the rat forepaw is a widely used model to investigate the functional organization of the somatosensory cortex or to study the underlying mechanisms of the blood oxygen level-dependent (BOLD) response. In reality, somatosensory stimuli have complex timing relationships and are of long duration. However, by default electrical sensory stimulation seems to be performed at an extremely short pulse width (0.3,ms). As the pulse duration may alter the neuronal response, our aim was to investigate the influence of a much longer stimulus pulse width (10,ms) using BOLD fMRI during electrical forepaw stimulation. The optimal neuronal response was investigated by varying the stimulus frequency at a fixed pulse duration (10,ms) and amplitude (1,mA). In a parallel experiment we measured the neuronal response directly by recording the somatosensory evoked potentials (SEPs). Quantification of the BOLD data revealed a shift in the optimal response frequencies to 8,10,Hz compared with 1,Hz at 0.3,ms. The amplitude of the recorded SEPs decreased with increasing stimulation frequency and did not display any correlation with the BOLD data. Nevertheless, the summated SEPs, which are a measure of the integrated neuronal activity as a function of time, displayed a similar response profile, with a similar maximum as observed by relative BOLD changes. This shift in optimal excitation frequencies might be related to the fact that an increased pulse width of an electrical stimulus alters the nature of the stimulation, generating also sensorimotor instead of merely somatosensory input. This may influence or alter the activated pathways, resulting in a shift in the optimal response profile. Copyright © 2006 John Wiley & Sons, Ltd. [source] Measuring the effects of indomethacin on changes in cerebral oxidative metabolism and cerebral blood flow during sensorimotor activation,MAGNETIC RESONANCE IN MEDICINE, Issue 1 2003K.S. St. Lawrence The work presented here uses combined blood oxygenation level-dependent (BOLD) and arterial spin tagging (AST) approaches to study the effect of indomethacin on cerebral blood flow (CBF) and oxygen consumption (CMRO2) increases during motor activation. While indomethacin reduced the CBF increase during activation, it did not significantly affect the CMRO2 increase during activation. The ratio of the activation-induced CBF increase in the presence and absence of indomethacin was 0.54 ± 0.08 (±SEM, n = 8, P < 0.001), while the ratio of the CMRO2 increase in the presence and absence of the drug was 1.02 ± 0.08 (±SEM, N = 8, ns). Potential difficulties in estimating CMRO2 changes from combined BOLD/AST data are discussed. Magn Reson Med 50:99,106, 2003. Published 2003 Wiley-Liss, Inc. 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