Heather A. Drury

A Common Network of Functional Areas for Attention and Eye Movements

Functional magnetic resonance imaging (fMRI) and surface-based representations of brain activity were used to compare the functional anatomy of two tasks, one involving covert shifts of attention to peripheral visual stimuli, the other involving both attentional and saccadic shifts to the same stimuli. Overlapping regional networks in parietal, frontal, and temporal lobes were active in both tasks. This anatomical overlap is consistent with the hypothesis that attentional and oculomotor processes are tightly integrated at the neural level.

An Integrated Software Suite for Surface-based Analyses of Cerebral Cortex

The authors describe and illustrate an integrated trio of software programs for carrying out surface-based analyses of cerebral cortex. The first component of this trio, SureFit (Surface Reconstruction by Filtering and Intensity Transformations), is used primarily for cortical segmentation, volume visualization, surface generation, and the mapping of functional neuroimaging data onto surfaces. The second component, Caret (Computerized Anatomical Reconstruction and Editing Tool Kit), provides a wide range of surface visualization and analysis options as well as capabilities for surface flattening, surface-based deformation, and other surface manipulations. The third component, SuMS (Surface Management System), is a database and associated user interface for surface-related data. It provides for efficient insertion, searching, and extraction of surface and volume data from the database.

Mapping visual cortex in monkeys and humans using surface-based atlases

We have used surface-based atlases of the cerebral cortex to analyze the functional organization of visual cortex in humans and macaque monkeys. The macaque atlas contains multiple partitioning schemes for visual cortex, including a probabilistic atlas of visual areas derived from a recent architectonic study, plus summary schemes that reflect a combination of physiological and anatomical evidence. The human atlas includes a probabilistic map of eight topographically organized visual areas recently mapped using functional MRI. To facilitate comparisons between species, we used surface-based warping to bring functional and geographic landmarks on the macaque map into register with corresponding landmarks on the human map. The results suggest that extrastriate visual cortex outside the known topographically organized areas is dramatically expanded in human compared to macaque cortex, particularly in the parietal lobe.

Computerized mappings of the cerebral cortex: A multiresolution flattening method and a surface-based coordinate system

We present a new method for generating two-dimensionnl maps of the cerebral cortex. Our computerized, two-stage flattening method takes as its input any well-defined representation of a surface within the three-dimensional cortex. The first stage rapidly converts this surface to a topologically correct two-dimensional map. without regard for the amount of distortion introduced. The second stage reduces distortions using a multiresolution strategy that makes gross shape changes on a coarsely sampled map and further shape refinements on progressively finer resolution maps. We demonstrate the utility of this approach by creating flat maps of the entire cerebral cortex in the macaque monkey and by displaying various types of experimental data on such maps. We also introduce a surface-based coordinate system that has advantages over conventional stereotaxic coordinates and is relevant to studies of cortical organization in humans as well as non-human primates. Together, these methods provide an improved basis for quantitative studies of individual variability in cortical organization.

Functional Specializations in Human Cerebral Cortex Analyzed Using the Visible Man Surface-Based Atlas

We used surface‐based representations to analyze functional specializations in the human cerebral cortex. A computerized reconstruction of the cortical surface of the Visible Man digital atlas was generated and transformed to the Talairach coordinate system. This surface was also flattened and used to establish a surface‐based coordinate system that respects the topology of the cortical sheet. The linkage between two‐dimensional and three‐dimensional representations allows the locations of published neuroimaging activation foci to be stereotaxically projected onto the Visible Man cortical flat map. An analysis of two activation studies related to the hearing and reading of music and of words illustrates how this approach permits the systematic estimation of the degree of functional segregation and of potential functional overlap for different aspects of sensory processing. Hum. Brain Mapping 5:233–237, 1997.

Surface-Based Analyses of the Human Cerebral Cortex

This chapter reviews many technical as well as conceptual issues involved in the surface-based analyses of cerebral cortex. The degree of accuracy associated with different surface representations is an issue of particular importance. For some applications, it is sufficient to see results portrayed on a cortical surface that is topologically accurate (that is, has no holes or tangles), even if it contains substantial geometric inaccuracies or distortion. For other purposes such as morphometric analyses, it is desirable to know the precise extent of the cortical surface (plus its thickness) associated with specific regions that have been delimited geographically or functionally. The visualization and analysis methods discussed and illustrated in this chapter involve a variety of software packages. Some of this software has only recently been made available, and some of it is still under active development. The goal of surface reconstruction is to obtain an accurate representation of the desired cortical layer by a process that is reliable, efficient, and entails minimal user interaction. It is important not only to continue improving the accuracy of surface reconstructions but also to refine the methods for assessing uncertainties and regional biases in surface area measurements.

Spatial normalization of one-dimensional electrophoretic gel images

A strategy for using processed, digitized images of one-dimensional electrophoretic gels to facilitate the analysis of large sets of overlapping clones is described. The images are acquired from fluorescently stained gels or from transilluminated gel photographs using a cooled, solid-state charge-coupled device camera. By employing sets of bands in the size-standard lanes as reference points, all the gel images are spatially normalized to a common reference template. After normalization, lane images from different gels can be compared as though the gels had been electrophoresed under identical, uniform-field conditions. Applications of this procedure to the analysis of a large set of overlapping lambda clones from chromosome VII of Saccharomyces cerevisiae and to the estimation of fragment sizes are illustrated.

Maximum-likelihood estimation of restriction-fragment mobilities from 1-D electrophoretic agarose gels

We have developed a technique for finding maximum-likelihood estimates of DNA restriction- fragment mobilities from images of fluorescently stained electrophoretic gels. Gel images are acquired directly using a CCD camera. The likelihood model incorporates the Poisson nature of the photon counts and models the fluorescence intensity as the superposition of Gaussian functions (corresponding to the fragment bands) of varying magnitude and width. An expectation-maximization algorithm is used to find maximum-likelihood estimates of the number of fragments, fragment mobilities, widths of the bands, background contributions, and DNA concentration. This approach has several advantages. Closely spaced and overlapping fragments are accurately resolved into their components. No a priori knowledge of the number or positions of fragments is required. Fragment lengths estimated by the maximum-likelihood method from experimental data were compared to the known lengths of fragments generated from three different restriction digests of bacteriophage (lambda) DNA. Preliminary results using the maximum-likelihood method indicate residual sizing errors on the order of 1%.