Sleep 4.1 Exploring the ANS and Sleep Neurophysiology: Wearables and Biomarkers

• Alright, so this is the fourth talk in our wearable wearables in sleep research series.
• And today we'll be diving into autonomic nervous system and sleep neurophysiology, biomarkers and wearables. 
• So, before I proceed with the talk, let me briefly remind you of our broader webinar series, which spans the full spectrum of sleep science, much of it from a wearable perspective. And in our last talk we discussed PPG with a focus on biophysics and physi physiology. And today we will talk about autonomic physiology.
• As I mentioned, the next talk will be the second part of ANS and sleep, but the one following that will be about sleep regularity and how to calculate it and interpret it so we'll, we'll give you the date and time for that for the future as well. 
• So we're here to discuss the crucial interplay between sleep and autonomic nervous system or ANS.
• But why should we, as clinicians and scientists even care about this relationship? And I'll present three compelling reasons. First is to accurately assess sleep quality outside of the traditional sleep lab. We really rely on the physiological parameters that are directly regulated by ANS. Think HRV, PPG, blood pressure, body temperature, and even respirations.
• And these are not independent measures. They're all intimately linked and governed by the intricate workings of the autonomic nervous system during sleep. And so understanding the ANS is therefore paramount to interpret the data that we get from these home-based devices. Second, there's a strong, well-documented association between poor sleep and adverse clinical outcomes, and it's just not correlation.
• There's accumulating body of evidence suggesting that a dysfunctional ANS is a key mediator in this relationship, so conditions like hypertension, cardiovascular disease, metabolic disorders and even cognitive dis decline are all exacerbated by poor sleep. And often the underlying mechanism involves an imbalanced or overactive autonomic nervous system.
• Finally, if we understand how the ANS influences sleep, we can leverage that knowledge to optimize sleep so we can start thinking about creating the right autonomic environment. The ideal physiological state that promotes restorative sleep. So this door opens, this opens the door to targeted interventions, whether they be behavioral, pharmacological, or technological, all aimed at fostering healthy sleep patterns by modulating A ANS.
• So today's talk, I will explore the intricate relationship between sleep and the autonomic nervous system, focusing on both the neuroscience and the cardiovascular physiology. and instead of simply presenting data on heart rate and heart rate variability and blood pressure during sleep, I want to provide a framework for understanding why these changes occur, and we'll explore this relationship through two lenses.
• The Neurovisceral integration model highlighting the brain body connection, autonomic control, and the concept of yin and yang representing the dynamic balance between opposing physiological forces. And this is basically an information theory concept of self and not self. And this framework I, I hope, will help us contextualize the data and make the relationships between the autonomic nervous system and sleep much more memorable.
• So to start off, I think this slide requires very little introduction. We're aware of the two branches, the autonomic nervous system. Actually, there's three, the third one being the enteric nervous system, which we often ignore, but then we see that the two branches of parasympathetic, the sympathetic parasympathetic is important for rest and digest.
• Sympathetic is fight or flight, vagus nerve being playing prominently in the parasympathetic nerve, nervous system. However, to coordinate the autonomic nervous system, this balance between the parasympathetic and sympathetic really requires a village, a complex network of interconnected centers, often referred as the central autonomic network depicted here.
• At the base, we have sensory receptors such as baro receptors and chemo receptors, which detect physiological changes in the body and moving upward. The medulla and the lower pons. How center is responsible for basic reflexes that regulate cross our organ coordination, coordination. And here you'll find a lot of the nuclei associated with the parasympathetic, such as nucleus, ambiguous, and the dors of vagus mortar neuron, and then the RVLM associated with the sympathetic, nervous system.
• In the upper pons senders, you have the integration of ANS with pain perception, stress response, motor functions, and behavior. And then on top of that is the hypothalamus acting as a critical pattern generator, orchestrating stereotype responses through a combination of endocrine ANS and behavioral signals.
• Further integration involves stimulus driven responses, which involve learned emotional and memory related components and higher order autonomic networks that integrate the perceptual representation, the current, visceral and somatic states, and includes areas like the default MO network, the insular cortex, and singular cortex.
• And finally, the prefrontal cortex in the executive regions play key role in the goal formation and decision making. And according to neurovisceral integration theory, there is a bottom up process where information is integrated progressively as it moves up through these various uh, systems.
• There is also a top down process that facilitates control and agency. So let me give you a good example to sort of demonstrate this top, bottom, top down and bottom up, physiological process. So imagine like you're me and you're about to step on the stage to give an important presentation, and your body immediately begins gathering and transmitting data.
• So your heart rate increases sending in signals to your brain about your physiological arousal, your stomach tightens creating awareness of tension. Your palm becomes sweaty, signalling, potential stress, and you sense the room temperature, the audience size, and the spatial lay layout. And this information flows upward to integration centers, which includes the insula, the cingulate cortex, and the prefrontal cor regions, which provides a comprehensive status report.
• Of your internal, state and environmental conditions. Now simultaneously, you have higher brain regions exert control to align bodily responses with your goals. So your prefrontal cortex recognizes, I want to do a good job to deliver this presentation effectively. And so the executive network inhibits the excessive sympathetic activation that might impair in performance.
• Your cognitive or my cognitive reappraisal processes reframes the nervousness as helpful excitement. Then the attention networks focuses on resources, on task, relevant aspects of the environment and the memory systems retrieve practice content and prior successful experiences. So this top down regulation modulates the initial bottom up signals, creating an adaptive physiological state that supports your performance goals.
• So that in a nutshell, quickly summarizes the neural visceral integration theory and gives sleep a larger context of ANS, which might better understand its functions. And then I wanna talk about another broad perspective, which is much more conceptual and not validated in any way. I find it really helpful to understand and contextualize the multiple aspects of sleep, which you know, from g lymphatics memory consolidation to ANS physiology that we can continue to discover.
• And this is the Eastern concept of yin and yang, the complimentary opposing forces, and we could view wakefulness is yang, externally focused a time for action and expressing self. And sleep is yin. Internally focused a time for restoration and rebuilding self. And self, to me, is an informational theory construct.
• It is an integrated internal representation of our being, our body, our thoughts, our memories, and our continuous experiences. And so the autonomic nervous system, particularly it, it influences on its heart, mirrors this dynamic. So we will show that understanding this yin yang balance help us to grasp why the cardiovascular system behaves so differently in non REM and REM sleep and why sleep might be so vital.
• So wakefulness is the expression of self and open system with increased entropy. Sleep restores the self, a closed system decreasing entropy. And within sleep we'll see that the autonomic nervous system or orchestrates the shift with distinct cardiovascular profiles in Wake non REM and REM. And to understand sleep's role, let's consider the concept of self, our internal experience, and the not self, the external world.
• The boundary here represents the informational divide. From a biological and physical standpoint, there's something which is me. That is, which is not me. And so during wakefulness, the boundary between them represented by this circle is permeable. We actively engage with the not self taking in information, acting and learning, and also consuming physical foods.
• And so this constant interaction is essential. As we'll see, this interaction is dynamically regulated now during sleep. This boundary changes while the interaction between the self and not self is not completely eliminated. The boundary becomes significantly less permeable as the smaller arrows suggest.
• This shift reflects the sleeps inward focus, a prioritization of internal process crucial for restoration and the consolidation of self. And so this brings me to my overarching model, wakefulness non-REM and REM forms a continuous cycle each vital for maintaining, evolving our sense of self.
• During wakefulness, we expand self through exploration. Non-REM then re-establishes self-providing stability, and REM redefines the self-integrating new information. And then you start the cycle again. And I hope later in the talk I will detail the physiological mechanisms, particularly within the autonomic nervous system that underpin this essential cycle revealing how sleep contributes to a dynamic and coherent identity. 

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