Lucid dreaming is a very interesting phenomenon that perhaps gives us a peek into the inner workings of the human brain. I have had about a dozen lucid dreams in my life that I can remember. Normally while dreaming we are not aware of the fact that we are dreaming. Our dreaming selves accept the reality of the dream. During a lucid dream we become aware that we are dreaming, but we do not wake up. This state is inherently unstable and often results in actually waking up or dreaming that we wake up, which ends the lucidity.

The phenomenon of lucid dreaming was originally known from self report, but was first verified in a 1981 study in which subjects consciously gave a signal while lucid dreaming – they carried out predetermined actions in their dreams that resulted in “observable concomitants.”

One of the goals of lucid dreaming research is to determine what exactly is happening in the brains of those who are lucid while dreaming. One hypothesis is that part of the frontal lobes may be more active, allowing for greater self-reflection and reality-testing while dreaming. Preliminary studies, for example using EEG to look at brain activity during wakefullness, normal REM sleep, and lucid dreaming, suggested that lucid dreaming is a hybrid state between fully awake and REM sleep. The frontal lobes are more active in lucid states than normal REM, but not as active as fully awake.

A 2012 study looked at the neural correlates of lucid dreaming using EEG and fMRI scanning. They found:

“During lucid dreaming the bilateral precuneus, cuneus, parietal lobules, and prefrontal and occipito-temporal cortices activated strongly as compared with non-lucid REM sleep.”

These kinds of studies are helpful, but can also be difficult to interpret. The same parts of the brain may contribute to multiple networks and therefore functions in the brain. As you can see with this study, multiple areas may light up with a single activity. While looking for neural correlates has been hugely successful in understanding the brain, there isn’t always a simple one-to-one relationship between an activity and brain localization. (The low hanging fruit of simple correlations have been picked long ago.) Networks and brain function are both complex.

A 2013 study tested the frontal lobe hypothesis further by using transcranial direct current stimulation (tDCS) to stimulate the dorsolateral prefrontal cortex of lucid dreamers to see if it induced a lucid dream. This study did show an effect, but it was not strong and only showed in the frequent lucid dreamers.

Finally we get to a recently published 2015 study that looked at the gray matter volume of frequent lucid dreamers vs controls. They found:

Participants in the high-lucidity group showed greater gray matter volume in the frontopolar cortex (BA9/10) compared with those in the low-lucidity group. Further, differences in brain structure were mirrored by differences in brain function. The BA9/10 regions identified through structural analyses showed increases in blood oxygen level-dependent signal during thought monitoring in both groups, and more strongly in the high-lucidity group.

Many arrows seem to be pointing to the frontal lobes in lucid dreaming, which makes sense as that is the part of the brain that is most involved in reality testing, self-reflection, and metacognition (thinking about thinking). The authors in the 2015 study also conclude from this:

“Our results reveal shared neural systems between lucid dreaming and metacognitive function, in particular in the domain of thought monitoring.”

In other words, we possess brain structures, specifically the frontopolar cortex, that allow our brains to monitor, and to some degree control, their own activity. We experience this as thinking about our own thoughts; being self-reflective.

It is therefore likely that lucid dreaming is an epiphenomenon. It is not something that humans specifically evolved nor does it serve a specific adaptive function. It is simply something that occasionally emerges out of brain function that has a separate function, that of introspection. These structures may have or be part of a deeper function still, such as the ability to pay attention, and just be aware of our own stream of consciousness.

Further, wakefulness and REM sleep are distinct brain states but the separation between the two is not always clean. Actually, it’s remarkable that for the vast majority of the time the separation is complete and clean. However, occasionally hybrid states can emerge. One such hybrid state is lucid dreaming.

Another is hypnagogia or waking dreams. In such states we feel we are awake but dream-like hallucinations may still occur, along with sleep paralysis. Not surprisingly, such states occur in the transition from sleep to wakefulness (or vice versa) or when the system is stressed, by sleep deprivation or pathological sleep conditions.

Conclusion

Our brains are very complex and highly sophisticated machines, but they are machines. The more we study them, the more obvious that conclusion becomes. They are a bit glitchy and also a bit of a kluge. Their functioning can be altered by changing their anatomy or physiology, or by stressing the system beyond tolerance levels.

Lucid dreaming is just one example pointing to the fact that the brain is a biological machine. Lucid dreaming serves no obvious purpose, but it emerges from normal brain function as an occasional glitch. We can see anatomical and functional differences that correlate with lucid dreaming, and to some extent can preliminarily induce them simply by electrically stimulating the brain.

Further, lucid dreaming points to one of the “highest” brain functions that we possess – the ability to monitor and reflect upon our own thoughts.