Functional magnetic resonance imaging (fMRI) was used to identify and map the representation of the visual field in seven areas of human cerebral cortex and to identify at least two additional visually responsive regions.The cortical locations of neurons responding to stimulation along the vertical or horizontal visual field meridia were charted on three-dimensional models of the cortex and on unfolded maps of the cortical surface. These maps were used to identify the borders among areas that would be topographically homologous to areas Vl, V2, V3, VP, and parts of V3A and V4 of the macaque monkey. Visually responsive areas homologous to the middle temporal/medial superior temporal area complex and unidentified parietal visual areas were also observed. The topography of the visual areas identified thus far is consistent with the organization in macaque monkeys. However, these and other findings suggest that human and simian cortical organization may begin to differ in extrastriate cortex at, or beyond, V3A and V4.In contrast to our extensive knowledge of cortical organization in nonhuman primates, far less is known about the identity and topography of functional subdivisions in human cerebral cortex. In the macaque monkey cortex, 30 or more distinct visual areas have been tentatively identified (1). In the human brain, a strong case has been made for only two or three areas (Vi, V2, and middle temporal) (2, 4-6), though several additional areas have been proposed (6-11). Brain images produced by functional magnetic resonance imaging (fMRI) show signals that are thought to represent local changes in blood oxygenation. These changes can be elicited by sensory-evoked neural activity though other factors such as alterations in blood volume and proton movement may also contribute [for review, see DeYoe et al. (12)]. We have used this technology to chart several functionally distinct visual areas in the human. Preliminary reports of this work have appeared (13,14). MATERIALS AND METHODSTo map angular positions within the visual field, four male and two female subjects (ages 24-40 years old) viewed a flickering black-and-white-checkered hemifield that rotated slowly about a central fixation point during a fMRI scan. To map visual field eccentricity (distance from the center of gaze), subjects viewed an expanding checkered annulus. In this manner, neurons responding to stimulation at different locations in the visual field were activated at different times during the stimulus sequence. Corresponding differences in the temporal phase of the fMRI response thus identified the retinotopic locationThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 2382represented by each active site in the brain (12). A similar technique has been described by Engel et al. (15).To enhance activation of extrastriate cortex (12) and to help maintain attention and arousal, the subj...

Two years ago, we described the first droplet digital PCR (ddPCR) system aimed at empowering all researchers with a tool that removes the substantial uncertainties associated with using the analogue standard, quantitative real-time PCR (qPCR). This system enabled TaqMan hydrolysis probe-based assays for the absolute quantification of nucleic acids. Due to significant advancements in droplet chemistry and buoyed by the multiple benefits associated with dye-based target detection, we have created a "second generation" ddPCR system compatible with both TaqMan-probe and DNA-binding dye detection chemistries. Herein, we describe the operating characteristics of DNA-binding dye based ddPCR and offer a side-by-side comparison to TaqMan probe detection. By partitioning each sample prior to thermal cycling, we demonstrate that it is now possible to use a DNA-binding dye for the quantification of multiple target species from a single reaction. The increased resolution associated with partitioning also made it possible to visualize and account for signals arising from nonspecific amplification products. We expect that the ability to combine the precision of ddPCR with both DNA-binding dye and TaqMan probe detection chemistries will further enable the research community to answer complex and diverse genetic questions.

We describe computational methods for constructing three-dimensional models and unfolded, two-dimensional maps of the cerebral cortex. These methods consist of four procedures, including (1) sampling of a surface within the cortex, (2) reconstruction of a three-dimensional model of that surface, (3) unfolding of the surface to generate a two-dimensional cortical map, and (4) visualization of data on the model and the map. These methods produce structurally accurate representations of the cortex and have practical advantages over previous manual and automated approaches for flattening the cortex. We illustrate the application of these methods to neuroanatomical data obtained from histological sections of cerebral cortex in the macaque monkey. The approach should be equally useful for structural and functional studies in other species, including humans.

Under general viewing conditions, objects are often partially camouflaged, obscured or occluded, thereby limiting information about their three-dimensional position, orientation and shape to incomplete and variable image cues. When presented with such partial cues, observers report perceiving 'illusory' contours and surfaces (forms) in regions having no physical image contrast. Here we report that three-dimensional illusory forms share three fundamental properties with 'real' forms: (1) the same forms are perceived using either stereo or motion parallax cues (cue invariance); (2) they retain their shape over changes in position and orientation relative to an observer (view stability); and (3) they can take the shape of general contours and surfaces in three dimensions (morphic generality). We hypothesize that illusory contours and surfaces are manifestations of a previously unnoticed visual process which constructs a representation of three-dimensional position, orientation and shape of objects from available image cues.

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