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Neural activity in the brain is accompanied by changes in cerebral blood flow (CBF) and blood oxygenation that are detectable with functional magnetic resonance imaging (fMRI) techniques. In this paper, recent mathematical models of this hemodynamic response are reviewed and integrated. Models are described for: (1) the blood oxygenation level dependent(More)
We investigated the cortical mechanisms of visual-spatial attention while subjects discriminated patterned targets within distractor arrays. Functional magnetic resonance imaging (fMRI) was used to map the boundaries of retinotopic visual areas and to localize attention-related changes in neural activity within several of those areas, including primary(More)
The physiological basis of the blood oxygenation level dependent (BOLD) signal and its dependence on baseline cerebral blood flow (CBF) were investigated by comparing responses to a visual stimulus after physiological changes of the baseline. Eight human subjects were imaged with 3 and 4 T MRI scanners, and both BOLD signal and CBF were simultaneously(More)
The coupling between cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) during brain activation can be characterized by an empirical index n, the ratio of fractional CBF changes to fractional CMRO2 changes. Measurements of n have yielded varying results, and it is not known if the observed variability is due to measurement techniques or(More)
The blood oxygenation level-dependent (BOLD) responses to visual stimuli, using both a 1-s long single trial stimulus and a 20-s long block stimulus, were measured in a 4-T magnetic field both before and immediately after a 200-mg caffeine dose. In addition, resting levels of cerebral blood flow (CBF) were measured using arterial spin labeling. For the(More)
OBJECTIVE To determine cerebral energy status in patients with Huntington's disease (HD) and Parkinson's disease (PD). METHODS The study included 15 patients with DNA-proven, symptomatic HD and five patients with medically treated, idiopathic PD, all of whom were candidates for neurotransplant treatment, as well as 20 age-related normal subjects.(More)
Functional MRI in awake-behaving primates is an emerging tool for bridging the gap between human fMRI and neurophysiology information from nonhuman primates. We report the use of magnetite dextran nanoparticles (Feridex) as a blood-pool agent to enhance fMRI contrast-to-noise (CNR) in primate FMRI. The intravascular half-life of the magnetite dextran was(More)
BACKGROUND Schizophrenia subjects demonstrate difficulties on tasks requiring saccadic inhibition, despite normal refixation saccade performance. Saccadic inhibition is ostensibly mediated via prefrontal cortex and associated cortical/subcortical circuitry. The current study tests hypotheses about the neural substrates of normal and abnormal saccadic(More)
Brain nuclei directly receiving retinal projections are readily labeled in magnetic resonance images following intraocular injection of manganese (Mn). To assess whether Mn in retinal ganglion cell axons can be transsynaptically delivered to visual cortex, mice that had previously received intraocular Mn injection were anesthetized with isoflurane, and(More)
The ability to use fMRI in a monkey model would bridge the gap between the fMRI demonstration of cerebral activation in humans and the cumulative wealth of monkey data on the functional organization of the brain from single electrode mapping, radioisotope and histology studies. We report a new technique for fMRI in an awake co-operative rhesus macaque(More)