Spike Sorting

Spike sorting was performed offline using the graphical cluster-cutting software MClust (Redish, 2009). Sleep recordings before and after the behavioral paradigms were included in the analysis to assure recording stability throughout the experiment and to identify hippocampal cells that were silent during behavior. Clustering was performed manually in 2D projections of the multidimensional parameter space (i.e., comparisons between waveform amplitudes, the peak to trough amplitude differences, and waveform energies, each measured on the four channels of each tetrode). Only clusters that could be stably tracked across all behavioral sessions were considered to be the same cells and were included in our analysis. Auto-correlation and cross-correlation functions were used as additional separation criteria. Cells with an average firing rate of less than 6 Hz and waveforms longer than 200 μs were considered to be putative excitatory cells and included in analysis.