The local chapter of the Society for Neuroscience - the primary professional organization of my field - has a lot of student involvement. The students primarily work with the Brain Awareness Council to perform public outreach to schools and community organizations to teach about the brain. In a way they're doing very much the same sort of thing that I'm trying to do with this blog and with the Lab Rats' Guide to the Brain. In addition to their community education, they also like to engage in some "recreational" exploration of neuroscience and media. One way they do this is through what they call "Neuroscience and a Movie." Last night I had the honor to be one of the panelists for discussion of the movie Inception.
Regular readers of this blog will know that I have discussed in section in the context of both memory and sleep, but I thought that perhaps the movie and its use of neuroscience would be a good topic for today's blog -- in particular, some of the questions that were raised by the students - and discussed among the group with contributions by a clinician and research scientist.
- Is it true that the time really passes so quickly within dreams, and the deeper you go the faster it passes? One of the things that we've learned by studying memory in animals is that there is actually a form of "replay," during the first sleep period, of recent waking experiences. In rat studies we have found that neurons in the hippocampus respond when animals are in particular places. If an animal is running in a maze or an elevated track, these "place cells" fire in sequence and the animal passes into and out of the appropriate location in their environment. The cells that exhibit both a correlation and a sequential firing that represents their experience of various locations. The next time the animal is in a "slow wave sleep" episode, the same neurons will again become active with the same correlation and the same sequential firing; however, the sequence will be vastly reduced in time, requiring seconds as opposed to the minutes that may have elapsed as the animal ran through the environment. This is perhaps one explanation of how "time" in dreams can appear to be compressed relative to reality. Another explanation is that dreams retrieve memories and those memories come complete with a context and history. During injury retrieval of a specific memory may imply an elapsed period of time that never actually occurs. Anyone who has ever had a complete dream experience in the seven minutes between pressing a snooze button, and the subsequent alarm, has likely experienced the retrieval of a complete memory and context.
- Do people really dream when they're sedated? I was fortunate to have as a fellow panelist, a senior resident in neurology who helped fill in some of the details of clinical medicine and sleep studies. There are indeed sedatives that allow REM sleep and normal sleep cycles to occur, at the same time there are sedatives which suppress REM sleep while allowing other phases of sleep to occur normally. In fact there are some drugs that are abused in the name of promoting "lucid dreaming" so it depends very much on what specific pharmacological and sedative drugs are used.
- So what is "lucid dreaming?" Lucid dreaming is an attempt to utilize the fact that some dreams occur in the later stages of sleep when the patient is aware of the fact that they are dreaming and can attempt to influence the subject matter and memories invoked in the dream. In fact one of the techniques applied in sleep clinics for dealing with nightmares is to have the patient write out the events of the dream, and then take those events and write a new story with a better ending and less emotional content. The next time they go to sleep there to think about and mentally rehearse the story that they wrote. Personally, I don't know how successful this is, but it is one of the techniques that is often referred to in the context of lucid dreaming, and it does have some applicability with patients who suffer from frequent nightmares.
- Where do nightmares come from? Psychologists, clinicians and scientists agree that there are many sources of nightmares, but the most common is subconscious anxiety. A major purpose of dreams appears to be processing of memory and experience. Some of those memories include an emotional component, and when those emotions are reactivated along with the memory, they can influence the experience of the dream. Activation of limbic areas of the brain such as the amygdala and hippocampus can certainly add emotional content to dreams. In fact, the most common type of nightmare is not a specific frightening incident, but merely vague unease and anxiety.
- Does the last food we eat or last thing we do before bed really influence our dreams?This is really two questions, but in a sense, we already covered the second half in the preceding sections on lucid dreaming - and yes, being relaxed and in a pleasant mood does assist in producing pleasant dreams (see above). As for food, there are two components to the issue - first is that the process of digesting food involves release of hormones and neurotransmitters throughout the body to control the process of manipulating the gastrointestinal system and processing nutrients. GI activation elevates cholecystokinin (CCK), CCK is in turn associated with GABA-containing neurons, and GABA neurons form the major inhibitory network in the brain. Thus it is quite possible (although not necessary) that what and when we eat can affect brain function as we sleep.
- What is the "kick", and will it really wake you out of a dream? Many of us have experienced periodic limb and body movements that occur during sleep. Certainly, anyone involved in a long-term relationship and shares a bed, is aware of the fact that most humans move during their sleep. Typically this occurs when the brain is in the lightest sleep stage, however random movements can occur even when and deeper sleep. One of the reasons why we can dream movements and experiences and not actually move our arms and legs is that the neural motor signals are inhibited, however the brain does still receive information back from the lands about position and sensations while we sleep. Thus, in a light enough stage of sleep, the brain can become aware of the fact that it sends commands to move the body, but that the body doesn't respond. This is one reason why a common feature of dreams is the sensation of being unable to move or unable to speak. On the other hand random or periodic muscle movements return signals to the brain that are different than those of the dream. This dichotomy can be enough to interrupt a dream, or a can begin a totally new context, or new dream sequence. So the "kick" is a very real phenomenon in which sudden movements or sensations will interrupt a dream and rouse the patient even from deep sleep.
- How could a person dream for the entire time that there sedated, don't we only dream in REM sleep? The dreams that occur during REM sleep are among the most vivid that we experience, but we can still dream in other stages of sleep. There are typically three stages of sleep referred to by scientists and clinicians: first stage of sleep is very light and is characterized by a reduction in amplitude of the EEG particularly at frequencies above 20 Hz, with an increase in the alpha rhythm at around 10 to 15 Hz; stage II sleep is characterized by increased amplitude of very slow frequency waveforms of less than 10 Hz; stage III sleep again sees a reduction in overall EEG, with a predominant Delta rhythm of less than 5 Hz. REM sleep is interposed primarily in stage II, but can also occur when transitioning between different stages of sleep. Stage I sleep is very similar to a deep meditative state, and thus the patient can be quite aware of the fact that they are not fully awake and nor are they fully asleep. Most experiences of lucid dreaming (as well as early morning dreams) occur as a transition between stage I and stage II sleep. Even without the rapid eye movements characteristic of REM sleep, dreams can still occur as a function of memory recall and consolidation that occurs during the later stages of sleep.
- So what kind of sleepy we actually need? Do we have to have REM sleep, or stage II or certain percentage of stage III? What the most important for feeling restful is that our sleep experience includes a normal cycling from stage I to stage III and back with periodic bouts of REM sleep. REM sleep and slow wave sleep are very important for memory processing and the formation of long-term memory, while stage III sleep is important for resting the muscles of the body. Interruption of any of these stages of sleep -- for example a person with sleep apnea spends most of their time in stage I sleep since they tend to wake up from deeper sleep stages due to breathing difficulty -- can result in decreased memory, attention, and ability to make decisions.
- How much sleep do we really need? Persons who can exist and function normally with very short sleep are quite rare. Research over the past several years has demonstrated that teens, particularly high school students, require about 8 to 9 hours sleep, and they don't start normal cognitive function until relatively late in the morning -- about nine or 10 AM. As a person ages you are quite frequently here that they say they do not need as much sleep, however this is often compounded by the fact that it insomnia, aches and pains, anxiety often interrupt their sleep. In the words of my fellow panelist: "sleep debt is a debt that must be paid." Failure to get sufficient sleep causes accumulative degradation in our cognitive abilities. Determining how much sleep we need is something that is highly individual, and can really only be best determined arranging our sleeping environment to minimize interruption, maximize comfort, and then determine how long we sleep without an alarm waking us up. Keep in mind that the normal waking time in this instance is the first time would come awake, ignoring the fact that all too many of us will turn over an attempt to go back to sleep. It's possible to sleep too much, just as it is possible to sleep too little. Under ideal sleeping conditions most people will sleep continuously for about 6 to 8 hours. Persons who have not "paid their sleep debt" may very well still be tired and can sleep for additional hours, but the first waking is typically an indication that the body has completed an appropriate number of sleep cycles. A sleep cycle takes our brains from stage I down to stage III sleep and back again with a few REM sleep bouts interposed. Each cycle takes anywhere from 60-120 minutes, and is repeated throughout the night. Of course some people wake up after completing one or more of these cycles. In fact, researchers are now suggesting that historical writings indicate that in the absence of artificial lighting, alarm clocks and modern social demands, people used to sleep in two periods during the night. There are several historical sources that indicate that even up to a couple hundred years ago people would experience "First Sleep", wake up for a short period of one to perhaps two hours, and then return for "Second Sleep." According to the same sources it was not uncommon for neighbors to socialize during the period between first and second sleep. The experience of modern technology and modern society puts artificial limits on our sleep cycle, to the extent that nowadays most people get either too much or too little sleep.
- Is "weekend sleep" sufficient for reducing sleep debt? The practice of shortening her sleep on weeknights and sleeping in late on weekends is actually quite detrimental to development of a normal sufficient sleep cycle. We sleep best and most effectively when we go to bed and wake up at the same time everyday. Establishing such a cycle takes much longer than the five work days in a week, and interrupting that cycle to sleep longer on weekends actually prevents the establishment of a normal healthy schedule. We can sleep can assist in reducing our sleep debt, but for most effective memory, reaction time, and cognitive performance we need to schedule an appropriate amount of sleep everyday and reduce the accumulation of sleep debt.
I will share a final question that I was asked: "At the end of the movie, do I think Cobb was in the real world or dreaming?" In response I told them: "I saw the top begin to wobble, in all of the dream sequences the top never wobbled. I guess we'll never know if he was awake or dreaming until they make a sequel."