Figure 4.

Dendrogram-based grouping of similar LFPs. Even after maximizing the correlation between trials by phase-shifting them to correct for phase resetting effect, the distance to an average LFP “template” can be further improved by grouping LFP waveforms according to their Euclidian-based dendrogram (A). Depending on the cutoff threshold for the distance along a tree, we can have a very coarse representation with only one group (for distance larger than 40) or five groups for distance around 20 (see the shaded areas that mark different groups). As the dendrogram suggests, the average LFPs for the first three groups are quite similar (B). The average LFP for the last two groups are also very similar (C), but quite different from the previous three groups. The resulting rms error of a trial with respect to its corresponding group average is definitely an improvement over the simple averaging of all trials (see Figure 3D). Even though the group average could be pretty close to capturing features of individual LFP trials form the respective group, the delay time for phase space reconstruction has a wide range of values (D) and there is no obvious group correlation.