Functional MRI (fMRI) can detect blood oxygenation level dependent (BOLD) hemodynamic responses secondary to neuronal activity. The most commonly used method for detecting fMRI signals is the gradient-echo echo-planar imaging (EPI) technique because of its sensitivity and speed. However, it is generally believed that a significant portion of these signals arises from large veins, with additional contribution from the capillaries and parenchyma. Early experiments using diffusion-weighted gradient-echo EPI have suggested that intra-voxel incoherent motion (IVIM) weighting inherent in the sequence can selectively attenuate contributions from different vessels based on the differences in the mobility of the blood within them. In the present study, we used similar approach to characterize the apparent diffusion coefficient (ADC) distribution within the activated areas of BOLD contrast. It is shown that the voxel values of the ADCs obtained from this technique can infer various vascular contributions to the BOLD signal.
"ADC data without MION obtained from the large b-value pair were used (Fig. 6B)—six animals from TR = 0.5 s (red circles) and three animals from TR = 1.0 s (blue stars) data. Because the pre-stimulus baseline ADC value measured at the middle cortical ROI was 0.72 ± 0.04 × 10 −3 mm 2 /s without MION (n = 9 animals) and 0.74 ± 0.02 × 10 −3 mm 2 /s with MION (n = 7), we considered pixels with a baseline ADC ≤ 0.8 × 10 −3 mm 2 /s to be located within the parenchyma, the same cutoff chosen by Song et al. (Song et al., 2002a). Because the ADC of CSF is ~2.5 × 10 −3 mm 2 /s, pixels with significant CSF contribution are expected to have larger ADC values. "
[Show abstract][Hide abstract] ABSTRACT: The signal source of apparent diffusion coefficient (ADC) changes induced by neural activity is not fully understood. To examine this issue, ADC-fMRI in response to a visual stimulus was obtained in isoflurane-anesthetized cats at 9.4 T. A gradient-echo technique was used for minimizing the coupling between diffusion and background field gradients, which was experimentally confirmed. In the small b-value domain (b=5 and 200 s/mm2), a functional ADC increase was detected at the middle of the visual cortex and at the cortical surface, which was caused mainly by an increase in cerebral blood volume (CBV) and inflow. With higher b-values (b=200 and 1000-1200 s/mm2), a functional ADC decrease was observed in the parenchyma and also at the cortical surface. Within the parenchyma, the ADC decrease responded faster than the BOLD signal, but was not well localized to the middle of visual cortex and almost disappeared when the intravascular signal was removed with a susceptibility contrast agent, suggesting that the decrease in ADC without contrast agent was mostly of vascular origin. At the cortical surface, an average ADC decrease of 0.5% remained after injection of the contrast agent, which may have arisen from a functional reduction of the partial volume of cerebrospinal fluid. Overall, a functional ADC change of tissue origin could not be detected under our experimental conditions.
"Investigations of pathogenetic models should either be carried out in medication-free patients or the drug effects must be controlled with appropriate statistical procedures. Additionally, a multimodal MR imaging approach evaluating the vascular contribution to the BOLD-signal by adding diffusion weighted MR techniques  should be adopted in functional imaging research to enhance the result interpretation. "
[Show abstract][Hide abstract] ABSTRACT: Functional magnetic resonance imaging (fMRI) was used to determine the acute blood oxygen level dependent effect (BOLD) of neuroleptic drugs in healthy male subjects. Using a robust simultaneous visuo-acoustic stimulation paradigm fMRI measurements were obtained prior to as well as 1 h and 24 h after intravenous infusion of 5 mg haloperidol to six healthy young men. After the administration, subjects showed significantly reduced BOLD contrast in the middle occipital gyrus while BOLD contrast was increased in the lingual gyrus. This pattern normalised within 24 h. Our results emphasise the necessity to control for interactions through acute medication and confirm fMRI as a non-invasive method for studying cerebral psychopharmacological effects.
[Show abstract][Hide abstract] ABSTRACT: The first part of this review is concerned with studies of the effectiveness of various forms of cognitive training on the performance of younger and older adults. The second part of the review presents results from structural and functional neuroimaging studies that may speak to the issue of which neurobiological factors explain reduced plasticity in older age. Finally, in the concluding section, some important and unresolved issues for future research are highlighted. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
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