To sleep, perchance to dream

I’ve written a fair amount about sleep in the past. But there’s one thing that I haven’t yet written about as far as sleep is concerned – dreams. I dream a lot. Most mornings, I wake up with a memory of at least 1 of my dreams, if not pieces of many of them. It is an integral part of sleeping, therefore it is probably pretty important. I started looking into how and why we dream to answer a few of my questions about what makes it so important.

Let’s first deal with how we dream. Dreams occur during REM sleep, the part of your sleep cycle when your body is inactive and your brain is active. (To refresh your memory on the sleep cycle, you can read my entry “Zzzzz…” from September 21.) Dreaming seems to be based in very specific regions of your brain. Using a variety of technologies, scientists have found that the limbic system is the most active part of your brain during REM sleep.

The limbic system is a set of brain structures deep within your brain that has a broad effect. Overall, it regulates both the endocrine system and the autonomic nervous system. The endocrine system is responsible for the production of all the hormones in your body, and regulates metabolism, growth and development, tissue function and emotions. The autonomic nervous system is a master control system for your body, regulating body temperature, heart beat, digestion, breathing, and pupil dilation. The limbic system contains numerous brain structures to help it do all of these things, including the hippocampus (which regulates long-term memories), hypothalamus (which affects heart rate, blood pressure, thirst, hunger and the sleep/wake cycle), thalamus (which communicates with the cerebral cortex) and amygdala (which is involved in motivational stimuli such as fear and pleasure). It is also closely connected to the nucleus accumbens, which is the brain’s pleasure center.

During REM sleep, our brains are active. So why don’t our bodies respond by moving, like when we are awake? That’s because REM sleep involves not only the activation of the limbic system, but also the inactivation of the cells in the brain that control muscles. REM sleep also inactivates the part of the brain that handles judgment. This happens in the frontal lobe, one of the 4 hemispheres of the cerebrum. Inactivation of this judgment process means that we accept the bizarre and illogical features of our dreams as they happen, and easily forget them upon waking.

Okay, so we know at least a little of how we dream. Our brains activate the limbic system and inactivate our muscles and our judgment. But why do we do it? While there is no clear-cut answer, scientists have many different theories. Because the limbic system is involved in both sensory processing and emotions, many people have suggested that dreaming is a way for us to connect our emotions and our thoughts. This is the psychological school of thought, in which dreams are believed to help us deal with emotions and complicated thoughts that we can’t handle while conscious. Some, however, believe that there is a physiological basis for dreaming. This argument says that dreaming exercises the synapses in our brains while we are resting. When we are awake, our brains are processing billions of messages through our brain cells. Dreams would allow this continual flow of messages, even as our bodies and brains get the benefit of being asleep.

So let’s review. How do we dream? The answer lies in the regions of our brains that are active and inactive during REM sleep. Why do we dream? Who knows.

On a final note, here’s one interesting fact that I cam across in my research for this entry –the percent of our sleep that allows for dreaming decreases as we get older. Babies spend around 16 hours a day sleeping, and half of that is REM sleep. That’s 480 minutes a day. Adults (those over 50, anyways) only sleep around 6 hours per day. And only 15% of that time is spent in REM sleep. That’s only 54 minutes. What a difference age makes!