Activation of single whisker barrel in rat brain localized by functional magnetic resonance imaging.

The previously established cortical representation of rat whiskers in layer IV of the cortex contains distinct cylindrical columns of cellular aggregates, which are termed barrels and correlate in a one-to-one relation to whiskers on the contralateral rat face. In the present study, functional magnetic resonance imaging (fMRI) of the rat brain was used to map whisker barrel activation during mechanical up-down movement (+/- 2.5 mm amplitude at 8 Hz) of single/multiple whisker(s).

Image reconstruction of sequentially sampled echo-planar data.

For echo-planar imaging (EPI), failure to time-reverse alternate echoes results in aliasing in the image. We encountered image artifacts in EPI acquired on a system with sequential sampling. After examining the source of these image artifacts, we concluded that the artifacts were a result of the type of sampling method used in data acquisition and the way the time-reversal of alternate echoes was carried out prior to Fourier transformation.

Functional magnetic resonance imaging of human prefrontal cortex activation during a spatial working memory task.

High-speed magnetic resonance (MR) imaging was used to detect activation in the human prefrontal cortex induced by a spatial working memory task modeled on those used to elucidate neuronal circuits in nonhuman primates. Subjects were required to judge whether the location occupied by the current stimulus had been occupied previously over a sequence of 14 or 15 stimuli presented in various locations. Control tasks were similar in all essential respects, except that the subject's task was to detect when one of the stimuli presented was colored red (color detection) or when a dot briefly appeared within the stimulus (dot detection).

Dynamic magnetic resonance imaging of the rat brain during forepaw stimulation.

A magnetic resonance (MR) imaging brain mapping method was used to localize an activated volume of brain tissue in chloralose-anesthetized rats during electrical stimulation of the forepaw. Physiologically-induced changes are characterized by alterations of the magnetic properties of blood as determined by the oxygenation state of hemoglobin. Stimulation of the left forepaw led to an increase in MR signal intensity of the contralateral frontal and parietal cortices, which corresponded to forelimb motor and somatosensory areas.

Dynamic mapping of the human visual cortex by high-speed magnetic resonance imaging.

We report the use of high-speed magnetic resonance imaging to follow the changes in image intensity in the human visual cortex during stimulation by a flashing checkerboard stimulus. Measurements were made in a 2.1-T, 1-m-diameter magnet, part of a Bruker Biospec spectrometer that we had programmed to do echo-planar imaging.

Applications of nuclear magnetic cross-relaxation spectroscopy to tissues.

Magnetic cross-relaxation in aqueous heterogeneous systems is a long established phenomenon that makes the observable decay constants for the system mixtures of more fundamental relaxation times which characterize the relaxation of the coupled components. By exploiting the magnetic relaxation coupling between the water spins and the immobilized spins in a tissue, the water-proton-signal intensity may be used to map indirectly a frequency response that is directly related to the 1H NMR spectrum of the immobilized components of the tissue. This method is applied to a number of rat tissues to determine whether there are significant differences among tissues that might be exploited in applications of this experiment to diagnostic magnetic imaging.