Fig. 4.

Cortical cell fluctuations showed anisotropy. (A) An example of a displacement trajectory of a micropost over a 90-s interval. The red ellipse with semimajor axis λ₁ and semiminor axis λ₂ illustrates the computation of the anisotropy index λ₁/λ₂ for this trajectory via principal component analysis (λ₁/λ₂ = 1.91 in this case.). (B) Probability distribution of the anisotropy index λ₁/λ₂. Eyeguide highlights a power law tail for highly anisotropic trajectories. (C) Examples of posts with a range of λ₁/λ₂. (D) Probability distribution of the angle between the major axis of the fitted ellipse’s long axis and the direction of the micropost’s average traction force F. The solid line is a fit with full width 2σ = 107°. See SI Appendix, Methods for details. (E) Probability distribution of the fraction of a post’s fluctuations with λ₁/λ₂ > 5, measured over 1,800 s in 90-s intervals. Error bars were estimated as $1/\sqrt{N}$ for each bin in the probability distributions.