1. A Temporally Controlled Inhibitory Drive Coordinates Twitch Movements during REM Sleep 
Patricia L. Brooks, John Peever 
Current Biology 
Volume 26, Issue 9, Pages (May 2016)
DOI: /j.cub
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2. Figure 1 REM Sleep Duration Predicts Twitch Activity
(A and B) REM sleep duration predicts twitch activity. The number (A; r = 0.813; p < 0.001) and frequency (B; r = 0.382, p < 0.001) of masseter muscle twitches occurring in a REM period are positively correlated with the length of the REM sleep episode.
(C–F) Levels of glycine and GABAA inhibition vary as a function of REM episode duration. Effects of strychnine (Sty) and bicuculline (Bic) application on the correlation between the number (C) and frequency (D) of masseter muscle twitches occurring in a REM sleep period. The positive correlation between twitch number and REM bout length under baseline conditions (blue line; r = 0.813, p < 0.001) is strengthened by glycine and GABAA receptor blockade (red line; r = 0.837, p < 0.001) (E) Conversely, the positive correlation between twitch frequency and REM bout duration (blue line; r = 0.382, p < 0.001) is prevented by glycine and GABAA receptor antagonism (red line; r = , p = 0.362) (D).
See also Figure S1, showing the frequency of REM sleep episode durations.
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3. Figure 2 REM Twitches Follow a Temporally Defined Trajectory
Group data showing that basal muscle tone (A) and twitch activity (B–D) progressively increase across individual REM sleep periods. By dividing REM sleep episodes into quarters, we showed that basal muscle tone (A) and the frequency (B), duration (C), and amplitude (D) of twitches all progressively increase across REM sleep. Asterisks (∗) indicate statistically significant differences (p < 0.05) compared to the first quarter of REM sleep. a.u., arbitrary units. All values are means ± SEM. See also Figure S2, showing that REM duration does not affect the temporal pattern of muscle activity.
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4. Figure 3
A Glycine and GABAA Drive Underlies the Temporal Pattern of REM Sleep Twitches
(A) Representative electroencephalography (EEG) and electromyography (EMG) traces of masseter activity during REM sleep under baseline (top trace) and when glycine and GABAA receptors are blocked by strychnine and bicuculline perfusion at the trigeminal motor pool.
(B–E) Group data showing how glycine and GABAA antagonism (red lines) impacts basal muscle tone (B) and muscle twitch activity (C–E). Receptor blockade has no effect on the level or temporal distribution of basal muscle tone during normal REM periods (i.e., during saline, blue lines) (B). However, twitch activity is substantially affected by glycine and GABAA receptor blockade. The frequency of muscle twitches disproportionately increased in the first quarter of REM, such that the normal pattern of increasing activity across the REM period was nullified (C). The duration of twitches also increased in the last three quarters of REM; however, the pattern of progressively increasing activity remained intact (D). Twitch amplitude was not affected by receptor blockade (E). Asterisks (∗) indicate a statistically significant difference (p < 0.05) compared to the first quarter of REM sleep in the treatment group (red line); open circles (○) indicate a significant difference (p < 0.05) between same quarter in control versus treatment group, and “n.s.” indicates not statistically different (p > 0.05). a.u., arbitrary units. All values are means ± SEM.
See also Figure S3, showing that microdialysis probes were targeted to the left trigeminal motor pool.
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5. Figure 4
Model Explaining the Temporal Pattern of Motor Activity in REM Sleep
The top figure illustrates the progressive increase in basal EMG tone and twitch activity across normal REM sleep. The schematic graph below summarizes the putative transmitter mechanisms controlling this temporal pattern of activity. Based on our data outlined in Figures 2 and 3, we suggest that changes in motor activity patterns result from a balance of inhibition and excitation acting on skeletal motoneurons. Functional evidence shows that inhibition is maximal at REM onset and minimal at REM offset, whereas excitation is minimal at REM onset and maximal at REM offset. The dynamic balance between glycine and GABA inhibition and glutamate excitation is hypothesized to account for the augmenting pattern of basal tone and twitch activity across REM sleep. Impairments in this inhibitory-excitatory balance would affect REM motor control and could explain motor over-activity in RBD.
Current Biology  , DOI: ( /j.cub )
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