Figure 4.

Schematic illustration of bias in second-order sequence analysis due to unequal behavioural sampling. Following the general flow introduced in figure 2, unobservable underlying sequences (top) generate sequences of spiking activity (rasterplots) across two different hippocampal maps (equivalently, different arms of a maze). Differences in the data used to estimate tuning curves for the two maps, such as the number of trials and/or the amount of trial-to-trial variability in behaviour, can result in ‘clean’ tuning curves for one map (green tuning curves) and ‘noisy’ tuning curves for another map (blue tuning curves). Note that for the noisy blue map tuning curves the sequence of observed behavioural tuning curve peaks is now in a different order (red dots), resulting in differences in the sequence scores for the two maps, even though there is no underlying difference in replay content. (Online version in colour.)