Hi, my name is Dr. Eric Nofsinger. I'm the founder, director, and chief medical officer at Sarov, as well as an adjunct professor in the Department of Psychiatry at the University of Pittsburgh, School of Medicine. Today, we're going to be talking about sleep and psychiatric disorders. To review, there are some general relationships between sleep and psychiatric disorders that are important to understand. First, if you are evaluating patients with psychiatric disorders, it's important to know that they oftentimes have difficulty sleeping at night time. In addition, if you're evaluating individuals that come in with complaints of sleep problems, it's not unusual for those individuals to have psychiatric disorders and psychiatric disorders could be the cause of the sleep problems. We're going to review a variety of these relationships, and these relationships can be explained by understanding the overlap between the brain systems involved in the expression of sleep and those implicated in psychiatric disorders. Before getting into the psychiatric disorders themselves, I want to review a little bit about the neural mechanisms of sleep. And the perspective that I'm going to give is looking at the neurobiology of sleep of a functional neuro-anatomical standpoint, and a lot of the information will come from functional brain imaging studies performed during sleep. Sleep is a very mysterious state, if you will. It's an unusual state if we all think about the dreams and the cognitions, the memories that we have of our sleep state, they tend to be very bizarre dream-like, story-like, with lots of fanciful images. So, this is, if you will, the mental content of sleep. The question then is, how do we scientifically measure something that is as mysterious as the dream-like state of sleep, if you will? Science has come a great deal in terms of our advancements of understanding the relationship between cognitions and brain function. What I'm going to describe now is a functional neuro-imaging technique that has been used to describe what's happening inside the brain while we sleep at night time. This is an experimental setup in which there is a bedroom and you have an individual that is sleeping comfortably in their bed. There's a wall between the bedroom and the sleeping environment, and a technician on the other side of the wall who can monitor the sleep state using EEG electrodes. In addition, to collect the brain image, in this technique, we will use positron emission tomography in which a radioisotope is injected into an individual, and then the isotope circulates throughout the brain in order to produce an image of brain function while a person is asleep at night time. Here, we have a diagram of the metabolism and injection of the fluorodeoxyglucose, the FDG, which is tagged with a radio tracer, 18F. At the time that a brain state that we want to study occurs, there is the injection of the radioisotope. Over the next 20 minutes, the isotope and the FDG circulates throughout the body and the brain, and it's metabolized to a form that does not escape out of the cells. And so, eventually, we can take a picture of that metabolic activity in the brain to produce a PET image. That PET image corresponds to the areas of the brain that were active around the time of the injection. This is one way that we can image brain function, if you will, during sleep states. Eventually, once a number of individuals who have been studied, we can summarize all of the data in a group of statistical image, and through the magic of statistics, we can define what's happening in one brain state versus another. For example, we might be able to define what happens in rapid eye movement sleep versus waking, or non-rapid eye movement sleep versus waking. So, this is a general methodology then to define what's happening inside the brain when we're asleep at night time. This image shows a graphical representation of the different sleep stages that an individual will have across the night time. An individual starts off with wakefulness, and during wakefulness, brain activity and metabolic activity is at a high state across the 24-hour period. In contrast, when somebody first goes to sleep, within the first hour or two, they descend into stage III and IV non-rapid eye movement sleep. This is the most quiet period of brain function in a 24-hour period. Brain activity and metabolic activity is at an all time low, and it's thought that the brain enters into this resting state, if you will, during deep non-REM sleep. Eventually, the brain goes into another state of sleep called rapid eye movement state. Rapid eye movement sleep is an activated brain state, and we can see the level of activation here by the PET scan. The PET scan is showing metabolic activity that's comparable to that of wakefulness. Meaning that the REM sleep state is an active brain state, and it's really only different from wakefulness because we're unconscious, we're actually asleep. We're not aware of the brain activity or the mental activity that's happening during rapid eye movement sleep. Across the rest of the night, the brain oscillates back and forth between periods of inactivity and non-REM sleep versus higher degrees of activity in rapid movement sleep. And eventually somebody wakes up the next morning and brain state then becomes metabolically very active. So, across a night of sleep then, we can see that there are very broad fundamental shifts in metabolic activity and the levels of activity of brain function. So, in this past segment, we've had an opportunity to review on a very broad and global level the overall changes in brain function across the sleep-wake cycle. In the next segment, we're going to talk at a more anatomically-specific level about the changes in sleep-wake function across the sleep-wake cycle.
