Negative correlation between average speed and average turning angle naturally arises for sparsely sampled cell movement data

Mechanisms regulating cell movement are not fully understood. One major feature that may allow cells to displace far from an initial location is persistence, the ability to perform movements in a direction similar to the previous movement direction. The level of cell persistence is determined by the turning angles (angles between two sequential movement vectors). Several recent studies, including one in eLife \cite{Jerison.e20}, found that a cell9s average speed and average turning angle are negatively correlated, and suggested a fundamental cell-intrinsic movement program whereby cells with lower turning ability are intrinsically faster. Using simulations, we show that a negative correlation between the measured average cell9s speed and average turning angle naturally arises due to sampling when the frequency of sampling is lower than that of the cell9s decisions to change movement direction. Interestingly, assuming heterogeneity in the cell9s persistence ability (determined by the concentration parameter of the von Mises-Fisher distribution) but not in the cell9s speed results in high differences in measured average speed per cell and a strong negative correlation between cell9s speed and average turning angle. Our results thus suggest that the observed negative correlation between a cell9s speed and turning angle need not arise due to cell9s intrinsic program, but can be a simple consequence of experimental measurements. Additional analyses show, however, that while theoretically it is possible to discriminate between the alternatives when recording cell movements at high frequencies, experimentally high imaging frequencies are associated with increased noise, and this represents a major barrier to determine whether a cell-intrinsic correlation between cell9s speed and its turning ability truly exists.