We illustrate here that the participation of each neuron in the low-dimensional trajectory contains contributions from both its firing rate and its synchrony with other neurons. Hence changes to its participation correspond to changes in rate and/or synchrony. Note that as the participation quantifies each neuron’s contribution to multiple dominant patterns of activity co-variation in the population, so we expect only approximate correlations with the cruder, independent measures of rate and synchrony used here. (A) Example correlation between the evoked firing rates and participation scores of all neurons in one evoked population response. Participation is expressed as a percentage of the maximum score; the firing rate is calculated using all spikes from the offset of the stimulus to the end of the recording, and thus cannot capture contributions due to the decay or increase of rates. (B) Histogram of firing rate and participation correlations across all 30 programs. Firing rate explains on average (R2, red line) 50% of the variation in participation within an evoked response. (C) Example correlation between the change in firing rates and the change in participation scores across one pair of evoked responses in the same preparation. One circle per neuron; red circles indicate neurons labelled as strongly variant for this preparation (though not necessarily across this pair of responses). (D) Histogram of the correlations between change in rate and participation across all 30 pairs of programs (pairs [1,2], [1,3], and [2,3] within each preparation). Firing rate changes explain on average 23% of the variation in the change of participation (R2, red line). (E-H) As A-D, for synchrony and changes in synchrony. The synchrony of each neuron is calculated as the total absolute correlation of that neuron with all other neurons, given by its corresponding column of the pairwise correlation matrix between all spike-density functions after stimulus offset.