The effect of image scrambling on visual cortical BOLD activity in the anesthetized monkey.

We have investigated BOLD signal changes associated with scrambling natural images into different numbers of segments in visually modulated regions of the macaque monkey (macacca mulatta) brain. For 10 degrees x 10 degrees images, we observed that BOLD activity in primary visual cortex (V1) increased with scrambling, and then dramatically dropped for very highly scrambled images (128 x 128 segments). In extrastriate visual areas, BOLD signal levels did not distinguish between natural images and scrambled images, except that as in V1 very highly scrambled images led to a drop in BOLD activity.

Ultra high-resolution fMRI in monkeys with implanted RF coils.

Spatiotemporally resolved functional MRI (fMRI) in animals can reveal how wide-spread neural networks are organized and accompanying electrophysiological recordings can show how small neural assemblies contribute to this organization. Here we present a novel technique that yields high-resolution structural and functional images of the monkey brain with small, tissue-compatible, intraosteally implantable radiofrequency coils. Voxel sizes as small as 0.

Magnetic resonance imaging of neuronal connections in the macaque monkey.

Recently, an MRI-detectable, neuronal tract-tracing method in living animals was introduced that exploits the anterograde transport of manganese (Mn2+). We present the results of experiments simultaneously tracing manganese chloride and wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) to evaluate the specificity of the former by tracing the neuronal connections of the basal ganglia of the monkey. Mn2+ and WGA-HRP yielded remarkably similar and highly specific projection patterns.

Three-dimensional shape representation in monkey cortex.

Using fMRI in anesthetized monkeys, this study investigates how the primate visual system constructs representations of three-dimensional (3D) shape from a variety of cues. Computer-generated 3D objects defined by shading, random dots, texture elements, or silhouettes were presented either statically or dynamically (rotating). Results suggest that 3D shape representations are highly localized, although widely distributed, in occipital, temporal, parietal, and frontal cortices and may involve common brain regions regardless of shape cue.