Characterizing Sleep Spindles in Sheep

Spindle density correlates primarily with non-rapid eye movement sleep. A, A hypnogram for a single sheep is shown between sunset (t = 0) and sunrise (t = 10). Data are shown as the mean ± SEM. B, Power of spindle detections from the same EEG recording. A black dot marks each spindle detection. Detections from all channels are included. C, The proportional density of spindles detected (N = 6 sheep) in each vigilance stage. D, Proportional densities (N = 5 sheep) of spindles for the first three sleep cycles lasting 18 min. E, Proportional densities (N = 6 sheep) of spindles throughout a single night (normalized for the amount of NREM sleep in each hour period). W, wake; WU, wake with rumination; R, REM sleep (highlighted in red); NR, NREM sleep. NREM sleep is split into four subgroups (light green, S1; light blue, U1; dark green, S2; dark blue, U2).

Local and simultaneous spindle topography. A, Spindles that occurred locally (only in one channel) are shown as the proportion of the total number of local spindles that occurred, for each sheep. The size of each black dot represents the number of local spindles occurring in a particular channel. B, The data represent the occasions on which spindles occurred simultaneously in two channels. The size of the black dot is again representative of the number of spindles occurring at each electrode for each sheep. The pairing of spindles is shown by the color and size of the lines linking two dots. Thicker lines and darker colors mean the likelihood of spindles firing simultaneously in those two channels is higher. C, The mean of spindle pairings for all sheep (N = 6). D, Data show the distribution of spindles when four or more spindles occur simultaneously. Again, the proportion of spindles occurring in a particular channel is shown by the size of the back dot, and the likelihood of simultaneous occurrence of spindles is shown by pseudocolored lines linking the dots. E, Mean data for spindles occurring simultaneously in four or more channels are shown (all sheep; N = 6). F, Histograms show how many channels were involved in each spindle event, for each sheep. G, H, For pairs of spindles (G) and for spindles occurring in four or more channels (H), the relationship between the channels in which simultaneous spindles occurs is shown as heat maps. For G, where data from two simultaneous spindles are shown, the rows represent the total number of spindles occurring in a particular channel, and the columns show the channel in which the second spindle occurs. The data shown in H are similarly represented for spindles that occur in four or more channels.

Spindles during the night and day for a single sheep. A–C, Cumulative spindle plots show the rate of spindle occurrences during night 1 (A), day 1 (B), and night 2 (C). B′, The change in local and simultaneous spindle density as day sleep returns to day wake can be seen in the enlarged plot (indicated with an arrow). C′, A similar shift from sleep to wake, but in the night. Simultaneous spindles (occurring in more than one channel at a time) are shown in black. Local spindles are shown in red. D–F, Hypnograms show the changes in vigilance stage for the same sheep, during night 1 (D), day 1 (E), and night 2 (F). G–J, Spindle density in each channel for this sheep is shown for night 2 NREM sleep (G), day 1 NREM sleep (H), night 2 wake (I), and day 1 wake (J). The breaks in the data and axes at 5 h in the day recordings for B and E indicate the times at which battery changes occurred. This figure is extended in Extended Data Figures 4-1 and 4-2.