The stresses acting on the luminal surface of endothelial cells due to shear flow were determined on a subcellular scale. Atomic force microscopy was used to measure the surface topography of confluent endothelial monolayers cultured under no-flow conditions or exposed to steady shear stress (12 dyn/cm2 for 24 h). Flow over these surface geometries was simulated by computational fluid dynamics, and the distribution of shear stress on the cell surface was calculated. Flow perturbations due to the undulating surface produced cell-scale variations of shear stress magnitude and hence large shear stress gradients. Reorganization of the endothelial surface in response to prolonged exposure to steady flow resulted in significant reductions in the peak shear stresses and shear stress gradients. From the relationship between surface geometry and the resulting shear stress distribution, we have defined a hydrodynamic shape factor that characterizes the three-dimensional morphological response of endothelial cells to flow. The analysis provides a complete description of the spatial distribution of stresses on individual endothelial cells within a confluent monolayer on a scale relevant to the study of physical mechanisms of mechanotransduction.

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It is not known with certainty at which level of face processing by the cortex the distinction between a familiar and an unfamiliar face is made. Subdural electrodes were implanted under the fusiform gyrus of the right temporal lobe in a patient who developed an unusual inability to distinguish differences between faces as part of the epileptic aura ("all faces looked the same"). A cortical region located posterior to the epileptic focus was identified that exhibited a maximum evoked response to the presentation of facial images (N165), but not to objects, scenes, or character strings. Evoked potentials elicited by a variety of visual images indicated that any perturbation away from novel whole-face stimuli produced submaximal responses from this region of the right temporal lobe. Electrical stimulation of this region resulted in an impairment of face discrimination. It was found that presentation of familiar faces (grandmother, treating physician) produced a different response from that observed for novel faces. These observations demonstrate that within 165 msec of face presentation, and before the conscious precept of face familiarity has formed, this cortical region has already begun to distinguish between a familiar and an unfamiliar face.

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