The nucleus acts as a ruler tailoring cell responses to spatial constraints.

The microscopic environment inside a metazoan organism is highly crowded. Whether individual cells can tailor their behavior to the limited space remains unclear. In this study, we found that cells measure the degree of spatial confinement by using their largest and stiffest organelle, the nucleus. Cell confinement below a resting nucleus size deforms the nucleus, which expands and stretches its envelope. This activates signaling to the actomyosin cortex via nuclear envelope stretch-sensitive proteins, up-regulating cell contractility. We established that the tailored contractile response constitutes a nuclear ruler-based signaling pathway involved in migratory cell behaviors. Cells rely on the nuclear ruler to modulate the motive force that enables their passage through restrictive pores in complex three-dimensional environments, a process relevant to cancer cell invasion, immune responses, and embryonic development.

Depth in anticorrelated stereograms: effects of spatial density and interocular delay.

Disparity-based depth is not perceived in densely textured, anticorrelated random-dot stereograms (RDSs) whose elements carry opposite signs of brightness contrast on corresponding loci, as extant data show. We observed global depth in anticorrelated RDSs flashed repetitively with an interocular delay. During the delay time, a dot array in one eye was paired with a gray frame in the other eye and thus could interact with the negative afterimage of the contralateral dot array. A correlated RDS (e.g. 8 min arc dots, 50% density, 15-msec flash duration) lost depth with delays > 45 msec. An anticorrelated RDS, that was otherwise identical, showed robust depth when flashed with an interocular delay of some 60 msec. A delay was not always necessary to produce depth. At low dot density (1-2%), anticorrelated RDSs showed disparity-dependent local depth even when displayed continuously, or flashed simultaneously; as dot density alone was increased, depth was progressively lost. To make global depth visible in a dense RDS flashed with an interocular delay, the internal response had to be strongly biphasic. Our results support the generally held notion that cyclopean depth signals emerge exclusively from same-sign binocular cortical filters. However, the exclusionary rule may be invalid with respect to the processing of coarse local depth with figural stimuli. Relative depth between a pair of small dots was easily perceived when one of the dots was in opposite contrast, but the depth threshold was then about 0.5 log unit higher than with the same-contrast pair of dots indicating that the internal effects of contrast have not all lost their sign prior to binocular disparity processing. It remains to be determined whether depth can be perceived from edges of opposite contrast.

Actuarial aging rate is not constant within the human life span.

It is often believed that the mortality intensity in the modern human population undergoes an exponential growth after 40 years, i.e. the actuarial aging rate is regarded to be constant after 40 years. To check this assumption we have calculated local aging rate values for 13 age ranges (within the interval of 30-92 years) for the male and female population of 48 states of the US (1969-1971). It was found that generally the male aging rate is not constant but lowers monotonically with time, while for females the aging rate has a pronounced approximately-shaped character with a minimum in the range of 45-60 years and a maximum within the range of 70-80 years. The results obtained are a warning to those who boldly use Gompertz or Gompertz-Makeham formulas when describing human aging on the population level.

Binocular disparity processing with opposite-contrast stimuli.

Stereoscopic perception of relative depth with reversed-contrast half images differs in several important respects from stereopsis with matched-contrast half images. Thus, reversed-contrast images show no correlated shift in visual direction, indicating that the sensory-fusion mechanism ignores opposite-sign edges; one experiment addressed this aspect of the problem. Mainly, this was a quantitative study of opposite-contrast stereopsis, in which stereoacuity was measured as a function of bar width by means of narrow-band stimuli. Acuity was about an order of magnitude worse for reversed-contrast than for matched stimuli, but the ability to see valid (disparity-dependent) depth was not altogether lost even with wide (1 cycle deg-1) reversed-contrast bars. It is generally believed that depth with opposite-contrast stimuli is mediated by interaction between binocular stimuli components that have the same sign of contrast. Perceived depth was measured as a function of disparity and thus one of the predictions of that 'same-sign hypothesis' was tested experimentally; then, the magnitude of same-sign components was manipulated within the reversed-contrast stimuli, and thus the general prediction of the same-sign hypothesis was tested. The results show conclusively that the same-sign hypothesis cannot account for opposite-contrast stereopsis; its mechanism remains unknown.