After understanding these global states, we now turn our attention to what's happening in different brain structures and the question here. Are there certain brain regions that are either more or less active in different brain states and can that tell us something about the function of that state of sleep? Here we can see pet images in which the blue areas represent reductions in metabolic activity during sleep, especially during deep stage three and four sleep in relationship to wakefulness. On the left-hand side images, you can see that they're very, very large regions of the brain, especially in frontal cortex, parietal cortex and the temporal lobe where there are dramatic reductions in metabolic activity during deep sleep during stage three and four non-REM sleep. Functionally, these are the areas of the brain that are very important for waking cognition and for executive function of the brain. These are the areas of the brain that, if you will subserve consciousness. So when we're conscious and awake, our executive brain function is activating at a very high-level. And when we're asleep in contrast, these are the areas of the brain, if you will go offline or have large reductions in metabolic activity and that constitutes the restful sleep state. On the lower image, we can see that the thalamus is also an area of the brain where there's a significant reduction in metabolic activity. The thalamus is the relay station for all of the sensory information that we receive in the external world to get into the brain and the reduction in metabolic activity in the thalamus represents, if you will a shutting off of the brain from the outside world. So vision, feeling, touch, smell, taste. These sensations are no longer growing from the environment and getting into the brain. It protects the brain state, if you will, so that it can be in this restful state in which it's not aroused at night time. So this then is the functional neuroanatomy of deep, healthy non-REM sleep. If we think about non-REM sleep and psychiatric disorders, if there are any alterations in non-REM sleep in specific psychiatric disorders, it may reflect an abnormality in function of these regions of the brain, heteromodal association as well as executive cortex. So we've identified the areas of the brain that are involved in non-REM sleep. If non-REM sleep is disturbed in a particular psychiatric disorder, it may be a reflection of an alteration and function in this circuitry in that specific specific group of individuals. Let's talk for a moment about the functional neuroanatomy of the other brain state of sleep, which is rapid eye movement sleep. Rapid eye movement sleep is the period of sleep that we most associate with dreaming at nighttime. If you ca think for a moment about your dreams, they can be very elaborate, storied images. Very emotionally charged images. So dreams are wonderful, mystical, magical. Oftentimes, artists will depict dreams in very fanciful ways. So there's something very unique about this aspect of sleep versus other aspects of sleep. These images show that on a global level during rapid eye movement of sleep, the brain is as active as it is during wakefulness. The top three images in the top row labeled awake shows different sections that were cut through the brain and pad images, and metabolic activity In those regions. And you can see that there are very, very high levels of activity in the cortex, in the superficial cortex during wakefulness. The lower row labeled rapid eye movement sleep show the same exact cuts through the brain, and pet images that were taken during rapid eye movement sleep rather than wakefulness. The main story here is that the levels of metabolic activity seen during rapid eye movement sleep are very comparable to those during wakefulness. So the brain is in an activated state, if you will d uring rapid eye movement sleep. Again, the major difference then between REM sleep and wakefulness is that the person is unconscious or not aware of brain activity that's happening to them. In these images, we now look at the regional neuroanatomical level and the question here is, are there specific regions of the brain that are involved with the generation of the use wonderful images and stories that produce our dreams at night time? What are the brain regions that create our dreams at night time? In these images, we show metabolically active regions of the brain during rapid eye movement sleep or during dreams. So when you're dreaming or when a healthy individual is dreaming at night time, the areas that are highlighted in these images and the reds and yellows and greens are the areas of the brain that are more active in dreaming sleep than they are wakefulness. If you will, these are the substrates or the neuroanatomical structures that give rise to the dream states. If we look at the general pattern that's emerging and the image on the left-hand side, the lower panel, we can see that it's a very midline degree of activation. It's not the lateral or outside cortex. It's very midline in nature. When we look at the image above that, we can see that there is a frontal distribution. This is actually the activation of medial prefrontal cortex, the anterior singulet cortex, the amygdala, the ventral striatum. These are all very primitive structures of the brain. These are all areas of the brain that are not so much involved in executive function, but rather are considered limbic and paralimbic structures. The limbic system in general is our emotional brain and that's what creates a lot of our strong emotions. Anger, fear, sexual interest, drives, thirst, hunger. These are the behaviors that the limbic system subserves, if you will. So in these images, we now see that it's these limbic and paralimbic. These emotion centers of the brain that tend to be activated more during rapid eye movement sleep. If we look specifically at the individual structures, we can kind of reverse engineer, if you will the function of dreams at night time. It's on the left-hand side are the structures activated in rapid eye movement sleep, including the interior paralimbic cortex, the ventral striatum, basal forebrain and basal ganglia, the pre motor region, primary sensorimotor cortex, cerebellum, insular cortex, mesial temporal cortex including the hippocampus. The memory center of the brain as well as the amygdala, the emotional center of the brain and also the brainstem reticular formation. We know that these brain structures have particular behavioral roles. The anterior paralimbic cortex, for example is involved in the detection of errors. If we are making a mistake, the anterior paralimbic cortex recognizes that becomes aware and activates. Other behaviors associated with these limbic and paralimbic structures include the motivation to action, a motivational aspect. Central pattern generation. Meaning, the programming of complex movements or behaviors, sensory motor functions, cognitive planning. The insular cortex involved with interface with the internal milieu, the stomach, if you will connected to the brain. And then large regions of the brain that have to do with emotion and the formation are activated during rapid eye movement sleep. If you will, we can put all of these structures together and their behavioral functions in what I think of as a reasonable concise description of the function of rapid eye movement sleep or dreaming. So I would tend to think of REM sleep is associated with the activation of a primal neural network, this limbic and paralimbic system in which the self is monitored inherent conflicts detected, perhaps by relating current behaviors to emotional memories. Then behavioral responses to the conflicts are either newly developed, modified or rehearsed. If you will, we've been able to go from psychological theories about dreaming to a brain based model of dreaming. If we think about psychiatric disorders now in rapid eye movement sleep, many of the psychiatric disorders have disturbances in rapid eye movement sleep. This may be related to the activation of limbic and paralimbic cortex in rapid eye movement sleep. The emotion centers of the brain, it's not unusual to think that they may be disturbed in people that have psychiatric disorders. The psychiatric disorders are disorders of emotion and cognition, if you will. And so alteration in rapid eye movement sleep found in a certain psychiatric patients could reflect abnormalities in this anterior paralimbic system of the brain. In this past segment, we have talked in a general sense about the functional neuroanatomical changes in healthy sleep across the sleep wake cycle and we've introduced. Some ideas about what might be happening in psychiatric disorders. In the next segment, we're going to move specifically to individual psychiatric disorders. Describe the sleep changes in those disorders and give a little bit of an understanding of the neurophysiology of those disorders based on their sleep changes.
