Phycology of sleep

in this talk we're going to review sleep and sleep disorders and this is one of my favorite talks who doesn't like to talk about sleep so let's start with an introduction to sleep why do we sleep well the truth is we don't really know we know if we impair sleep there's abnormalities in temperature regulation problems with memory and cognition and altered homeostasis so presumably sleep is important in managing temperature memory cognition and body homeostasis but we really don't know all of the aspects of why we sleep and and the important features how long should we sleep well the answer probably is as much as you can and more sleep is good and the amount that we sleep and the quality of our sleep does vary over the course of a lifetime what changes with sleep as we age a lot and we'll dive into that more in this talk so let's start with the discussion of sleep physiology when you think about wakefulness and sleep I want you to think about the yin and the Yang of the Wake promoting areas of the brain and the Sleep promoting areas of the brain first let's talk about the left part of the slide the arousal and activating system this starts down in the brain stem in the reticular activating system which turns the brain on the key anatomic structures of the brain stem Thalamus and hypothalamus and the brain chemicals that pre play a role in activating the brain are acetylcholine histamine dopamine serotonin and norepinephrine and these turn the brain on on the opposite side we have the Sleep promoting system which puts us to sleep and the critical structures there are the hypothalamus and ventrolateral preoptic nucleus and a number of brain chemicals including Gaba so when we think about sleep physiology one of the things that I want you to take away is how the brain is turned on how do we wake ourselves up well the suprachiasmatic nucleus of the hypothalamus is critical in the morning when light hits our eyes or we open our eyes that light stimulus travels back through the optic nerve to the optic kaym and there's a small branch of neurons that send that information up to the supermatic nucleus of the hypothalamus and this will ultimately turn the brain on you can see here the suprachiasmatic nucleus or scn projects neurons to the hypothalamus from the hypothalamus signals are sent to the brain stem and the reticular activating system the reticular activating system or Ras is what turns the rest of the brain on and you can see here projections throughout the cortex to turn the brain on and so this is a critical regulator of how we turn the brain on and wake up during the day the second system I want you to think about is the Circadian rhythm and melatonin which is one of the key Regulators that puts us to sleep so let's walk through this slide and understand what's happening in the brain we're going to start down with starting your day light hits your eyes that information is traveled to the supermatic nucleus and this turns the brain on as we go through our day we reach maximum arousal fast reaction times we can limit caffeine intake ultimately reach the end of the day when melatonin release starts melatonin is one of the key Regulators that puts the brain to sleep and we see about an hour after that dramatic melatonin release the brain and body become sleepy we sleep through the night we see the temperature reaches its lowest point during the night we have both deep sleep early in the night and rim sleep later and then as melatonin release stops the brain is ready to wake up and the Circadian rhythm is one of the important automatic controls of wakefulness and sleep when we think about melatonin melatonin and cortisol um are important in their interaction to put us to sleep and wake us up and you can see here the changes in brain and body melatonin and cortisol when we wake up melatonin is going down and cortisol is spiking to wake us up and get us active and moving in our day over the course of the day cortisol levels Decline and melatonin builds up right before sleep and so in this way these hormones help to control both the the brain and the body's wakefulness and sleep and are critical Regulators in situations where there's dysfunction of melatonin or problems with cortisol function we'll see abnormalities in circadian rhythm and both wakefulness and sleep stress can also change a number of these hormones and either disrupt sleep or change our ability to remain fully awake when we think about sleep there are a number of stages and we can understand those by their description what's happening for the patient and changes in the brain and we evaluate those with EEG or electroencephalography so let's walk through some of those stages of sleep the first is the awake stage and we can be awake with our eyes open or awake with our eyes closed when we're awake with eyes open the person is alert and active and there are prominent beta waves low amplitude very high frequency waves because the brain is thinking and there's stimuli and things going on when we close our eyes there's a reduction in the stimuli that are entering our brain Through The Eyes we see a decreased level of alertness and a relaxation of the brain and accordingly we see the development of alpha waves on the brain as that basil Rhythm comes out and there's a reduction in all of that high frequency thinking that occurs when the eyes are awake and open as we move into sleep the first part of sleep early in the night is non RM sleep and the first stage of stage one this is characterized by a transition from wakefulness to sleep patients become somnolent or drowsy during that early phase and this is the lightest sleep typically the EEG pattern during that stage one of sleep are theta waves as the brain moves from the alpha calm of wakefulness to the Deep Sleep of Delta wave sleep stage two sleep is characterized by patients becoming less responsive and the brain is going deeper and deeper into sleep the heart rate goes down temperature begins to decrease and the body prepares for deep sleep as well as Rim sleep this is the longest stage in terms of the total duration of sleep calculated over the course of the night and on EEG we see theta waves sleep spindles which are bursts of high frequency low amplitude activity and K complexes which are large discharges of waves the sleep spindles help to put the brain to sleep and those K complexes help to maintain arousal in case the body needs to wake up for any um any reason and then the brain moves into slow wave or deep sleep and this is charactered by stage three um sleep in this stage restfulness occurs this is the deepest part of sleep it is much more difficult to arouse individuals from this deep stage three sleep body tissue growth occurs this is where the brain and body will repair and this decreases in duration over the course of life with age here we see on the EEG delta waves these are the highest amplitude lowest frequency waves as the brain is very calm and relaxed and in deep Sleep next we see Rim sleep and the majority of Rim sleep occurs very late at night after the onset of deep or slow wave sleep Rim sleep is our Dream sleep and this is where the body and brain will dream the EEG shows mixed low voltage pattern in fact it looks very much like an awake brain on the EEG if we look at um Electro ular uh recordings we see rapid eye movements and that's what's characteristic of this phase of sleep the eyes are moving and we can see that both on the electrodes as well as just looking at a patient's eyes we see irregular sharply Peak eye movements during this phase and very importantly if we record muscle activity through an EMG we see atonia of voluntary muscles we don't need to be acting out our dreams and so during Rim sleep the body and muscles um have no tone and there's no movement inactivity due to inhibited Alpha motor neurons in certain disorders like Rim behavior disorder the brain lose and body loses this atonia with the ability to act out dreams and that's Rim behavior disorder on the EEG it looks very much like someone who is awake there are beta waves those high frequency low amplitude waves um that occur during Rim sleep so let's look at some of those EEG patterns in normal wakefulness we see Alpha and beta waves you can see they're very low amplitude and high frequency as the brain is thinking and processing stimuli and many things are happening in the brain in stage one sleep as the brain prepares uh for sleep we we see theta waves slightly higher amplitude slightly lower frequency as the brain moves into a slower wave of sleep in stage two there's this competition between sleep promoting signs and wakefulness promoting activity the sleep spindles are these really high frequency low amplitude spindles that put the brain to sleep and the K complexes are around complexes all occurring on top of those theta waves and findings on the EEG that appear um as you see here are indicative of stage two sleep slow wave sleep that you can see here is very high amplitude low frequency waves um that give this stage of sleep its name of slow wave sleep and here we're looking at delta waves and then as we move into Rim sleep we see the brain really looks awake we see The Return of beta waves low amplitude High activity as the brain is processing all the things that are happening uh during those dream states now let's talk about some of the environmental factors that are associated with sleep and impairments in sleep alcohol can significantly change sleep and reduce the amount of Rim sleep that the body will experience over the course of night caffeinated drinks change our ability to get to sleep and maintain a high quality of sleep large meals before bedtime change the ability of the brain and body to get into that Rim sleep and the duration of slow wave sleep exercise can impact sleep napping during the day can impact sleep light exposure around bedtime also changes activity of that super chiasmatic nucleus and can alter the ability to get to sleep nah