Luminance contrast of a visual stimulus modulates the BOLD response more than the cerebral blood flow response in the human brain.

The blood oxygenation level dependent (BOLD) response measured with functional magnetic resonance imaging (fMRI) depends on the evoked changes in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO(2)) in response to changes in neural activity. This response is strongly modulated by the CBF/CMRO(2) coupling relationship with activation, defined as n, the ratio of the fractional changes. The reliability of the BOLD signal as a quantitative reflection of underlying physiological changes depends on the stability of n in response to different stimuli.

HIV and chronic methamphetamine dependence affect cerebral blood flow.

Human immunodeficiency virus (HIV) and methamphetamine (METH) dependence are independently associated with neuronal dysfunction. The coupling between cerebral blood flow (CBF) and neuronal activity is the basis of many task-based functional neuroimaging techniques. We examined the interaction between HIV infection and a previous history of METH dependence on CBF within the lenticular nuclei (LN).

HIV infection and aging independently affect brain function as measured by functional magnetic resonance imaging.

We investigated the interactions between human immunodeficiency virus (HIV) infection and aging and their effects on brain function demands by means of functional magnetic resonance imaging (fMRI). A multiple-regression model was used to study the association and interaction between fMRI measures, HIV serostatus, and age for 26 HIV-infected subjects and 25 seronegative subjects. Although HIV serostatus and age independently affected fMRI measures, no interaction occurred.

Effects of aging on cerebral blood flow, oxygen metabolism, and blood oxygenation level dependent responses to visual stimulation.

Calibrated functional magnetic resonance imaging (fMRI) provides a noninvasive technique to assess functional metabolic changes associated with normal aging. We simultaneously measured both the magnitude of the blood oxygenation level dependent (BOLD) and cerebral blood flow (CBF) responses in the visual cortex for separate conditions of mild hypercapnia (5% CO(2)) and a simple checkerboard stimulus in healthy younger (n = 10, mean: 28-years-old) and older (n = 10, mean: 53-years-old) adults. From these data we derived baseline CBF, the BOLD scaling parameter M, the fractional change in the cerebral metabolic rate of oxygen consumption (CMRO(2)) with activation, and the coupling ratio n of the fractional changes in CBF and CMRO(2).