Anisotropy of cortical fluctuations. (A) A displacement trajectory for a micropost adherent to a CMF cell over a 90-second interval. The red ellipse with semimajor axis λ₁ and semiminor axis λ₂ shows the calculation of the anisotropy index λ₁/ λ₂ using principal component analysis. (B) Probability distributions of the anisotropy index for (B) different cell types and (C) for 3T3s on substrates of different stiffness show apparent high-anisotropy power-law tails as compared to that computed for an isotropic random walk (dashed red lines). (D) Examples of posts adherent to a CMF cell with different values of λ₁/ λ₂. Error bars were estimated as |$1/\sqrt{N}$| for each bin in the probability distributions.