Sleep 4.5 REM Physiology

• Now, how about REM physiology?
• Now, this is different, when it comes to REM physiology. When we return to our self and non-self model, we come with sort of a little bit of a difference. While non-REM consolidates existing internal representations, REM, I believe, is crucial for redefining self, and this stage is characterized by active parasympathetic and active sympathetic activity, creating sort of a more chaotic dynamic and heterogeneous physiological state. And this is a state which is internally focused, but also receptive to the new information acquired earlier in the day, incorporating the day's experience and updating our internal models. This internal, representation, I believe is how REM sleep contributes to an involving adapting sense of self.
• And so let's revisit this with heart rate, and focusing now on REM sleep. Again, we have the hypnogram above and the institutional heart rate below. And in stark contrast to the stability of non-REM, you notice the really highly variable nature of heart rate during REM sleep. The periods in between the great bars, is sort of a contrast, which is the non-REM sleep.
• This rapid fluctuations reflect the dynamic interplay, the sympathetic and the parasympathetic, nerves. And this chaotic, unpredictable pattern is sort of a hallmark of REM sleep. We could see the same thing in heart rate variability during REM, using the same spectral analysis that we'd seen before.
• Again, we see the heart rate segments on top and their corresponding frequency components below. And unlike the decreasing total power non-REM, the total HRV power during REM increases and is much more variable. And while the proportion of high frequency HRV is elevated in deep non-REM. There's greater variability in high frequency power during REM and a shift towards lower frequency oscillations, which sort of reflects the dynamic inter deflate between the sympathetic and parasympathetic branches.
• And this is,if you recall our slide, showing so the sympathetic nervous activity in the leg. But now if you take a look at the REM sleep area, we see active bursts of sympathetic nerves with irregular frequent bursts. And this is also associated with elevated increases in blood pressure, and this confirms sort of the increased phasic sympathetic activation that is characteristic of REM sleep.
• It's not just temporal heterogeneity, but there's also regional heterogeneity. And this diagram illustrates how different organs receive distinct, sympathetic, signals. They exert differential control, which increases heart rate, so it increases activation of the sympathetic to the heart and to the muscles which causes increased vasoconstriction and reduces muscle blood flow, which corresponds with the muscle atonia. And then conversely, you have inhibition of the vascular system, the sympathetic system, which increases blood flow in the kidneys and the splanchnic system. So now we've seen that non-REM sort of reestablishes the self through internal synchronization, and REM contributes to redefining a new self by incorporating new information.
• But these are not isolated processes. They're sequential. So non-REM occurs predominantly early in the night. It is essential for preparing the system for REM just as you wouldn't sort of build a shaky foundation. The brain needs a clearing and stabilizing effect of non-REM, the detoxification, before it can effectively integrate new experiences during REM.
• So non-REMs action therefore sets the stage for successful redefining of self that occurs during REM sleep. And so this currently certainly can be seen from a neural level. Non-REM prepares for REM by priming. Priming the thalamic cortical network. During N3, the high amplitude sold slow delta waves reflect widespread neuronal synchronization, and this leads to high ization of thalamic neurons creating a period of quiescence or reset.
• As non-REM progresses, a gradual depolarization of these neurons occurs, and these depolarization thalamus is permissive to the propagation of the theta rhythm originating from the septal hippocampal system. So the N three to REM transition mediated by this thalamic priming is critical for subsequent memory consolidation.
• Cognitive processing and overall brain health that takes place during REM and so during wakefulness, we have constantly new connections strengthening synapsis as we've shown here on the left, but this cannot continue indefinitely because it will lead to saturation, hindering learning, and increasing noise.
• Non-REM slow wave sleep provides the solution of synaptic down downscaling, the delta waves, characteristics of deep sleep, along with low levels neuromodulation, promote long-term depression weakening, less important in connections, basically clearing out the waste as I discussed before. And this reset improves the signal to noise ratio and supporting sort of that coherent concept of self.
• While non-REM prunes sort of the less relevant connections, REM sleep actively strengthens and restructures remaining memories integrating them into the existing networks. This basically highlights sort of the REM which is important for emotional memory and procedural skill. 
• So, to summarize: Non-REM slow wave sleep and REM sleep plays distinct complimentary roles in memory. Non-REM with its slow oscillations and spindles and ripples is crucial for declarative memory consolidation. REM sleep and contrast with its data activity is critical for procedural memory, complex tasks and tasks and emotional memory achieved through synaptic plasticity.
• So I wanted to, I, I know we're sort of reaching, nearing the end, I wanna return to our overarching hypothesis. So we've journeyed through the distinct physiological landscapes of non-REM and REM sleep, and we've seen how non-REM, with its synchronized, internalized focused state enhances it reestablishes a coherent, stable sense of self.
• REM with this dynamic heterogeneous autonomic activity increases acetylcholine and capacity for synaptic plasticity and redefines the self integrating new information. And this is when we sort of had these aha moments, which can drive creativity in, I think the person who sort of discovered the structure of benzene rings had dreamt about it.
• And this happens because you have this generation of new connections that happens in REM sleep that doesn't happen in non-REM sleep. And we could consider this model of self. From within the context of sleep across lifespan. And this graph shows the dramatic shift in the sleep architecture from infancy to old age.
• And notice that much larger proportion of REM sleep in neonates, infants, and which gradually decreases as we age. Now, if REM sleep is crucial for redefining self by integrating new information. This makes perfect sense 'cause infants and children are constantly encountering novel experiences, rapidly expanding the understanding of the world in themselves.
• And this increased REM sleep I propose supports this accelerated period of self construction and development. So the longer time of sleep in kids also allows sufficient non-REM to support the REM sleep. Sleep as well. And so this is my complete model. It's a continuous cycle. During wakefulness, we engage with the world expanding ourself.
• Non-REM sleep then consolidates the experience, reestablish a stable, coherent sense of self clearing out noise and limiting waste. And REM sleep takes this consolidation self and redefines it integrates into new information forming new association and driving creativity. And interestingly, this cycle model of self maintained throughout the interplay of non-REM resonates with the ancient eastern eastern philosophy.
• The yin and yang symbol represents opposing at complimentary forces, and we can see non-REM as yin. The restorative internally focused state REM becomes yang within yin active, yet still within the realm of sleep. Wakefulness is Yang active and active, outwardly directed, and the concept of Siesta, a brief daytime sleep can be seen as yin within yang.
• And so this ancient wisdom, like our scientific model, sort of emphasizes the essential balance and interdependent interdependence of these states for overall wellbeing. 
• I think now that, um, we're at the tail end of this talk, I do have some, information about how, poor sleep could lead to poor cardiovascular outcomes, and I'll do that for part two.
• I apologize for sort of going a little bit over time and what I plan to do for part two of this talk. I will talk a little bit about what devices can practically measure autonomic nervous changes, how blood pressure fluctuates across these stages, how respiratory patterns change. And then I'll also talk about temperature as well.

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