Figure 6.

Most CA1 ripples are spatially confined. A, An example rat showing the recording locations along the septotemporal axis. SH, Septal hippocampus; IH, intermediate hippocampus; TH, temporal hippocampus. B, Single ripple events recorded from two sites. The temporal delay between the largest amplitude troughs are measured. C, Spatial synchrony of ripple waves. The percentage of ripple events detected in the referred electrode within ±1 ms of a ripple event in the reference electrode is plotted as a function of distance between the electrodes. Each dot is based on a single recording session. Dots are colored red if both electrodes of the recording pair were located in the septal-intermediate hippocampus, and blue if one of the electrodes in the pair was in the temporal hippocampus and the other in the septal-intermediate hippocampus. Note that ripple waves in large-amplitude ripple events (>7 SD group; left) spread larger distances than the medium or small ripple events (middle, 5–7 SDs; right, 3–5 SDs). D, Spatial synchrony of ripple events. Same as in C, but the referred events were detected within ±50 ms of the ripple event in the reference electrode. Note the large spatial coverage of large-amplitude ripples (>7 SDs) in the septal-intermediate hippocampus (red dots). In contrast, ripple event synchrony between septal-intermediate and temporal sites at similar distances (2.5 to 5 mm) was low (blue). E, An example continuous Morlet wavelet transform during a single ripple event centered on the ripple at site 1 (as in A). Note rapid attenuation of the ripple event amplitude with distance. F, Ripple event amplitude attenuation over distance. Ripple amplitude (at 0 time bin and mean over the 120–180 Hz range) was measured at all referred sites during each ripple event in the reference channel, and the means are plotted as a function of distance between the reference and referred electrodes (same color code as in C, D).