Recently I had a dream in which I was called upon to perform emergency surgery on someone outside of the hospital setting. (I am not a surgeon, and this is a bit of a recurring anxiety dream – as a doctor I may be called upon to do something I am not qualified to do, but as the most qualified person present may need to take responsibility for it.) In the dream I was told by a surgeon (and in the dream I did not question why they were not doing the surgery) that the person needed an emergency appendectomy. It did not strike me (my dreaming self) as at all odd that the person’s chest was exposed for surgery, rather than their abdomen, or that the patient was wide awake. My awake self, of course, laughs at the absurdity of the situation with the realization that I would have responded completely differently to the situation than my dreaming self.

Most people have noticed that dreams often have a surreal feel to them, or that your dream-self accepts as perfectly natural absurd occurrences and situations. I was recently asked about this on the SGU forums. Evil Eye asked:

Why when something …ESPECIALLY only one thing… is absurd… in a dream… do we still accept it as normal until we wake up and think about it?

The answer to this question is actually well known. First, we must understand a little bit about the nature of the self – our perception that we exist and are conscious. The self is the net effect of all the parts of our brains working together in real time. Thinking tasks are segregated to specialized parts of the brain, but they combine seamlessly to create the experience of one conscious mind, the self. If you remove or suppress the function of one or more pieces of the brain, then you change the net effect and therefore the self. Neuroscientists are doing this, in fact – using magnetic fields to suppress the functioning of pieces of the brain, while using functional MRI scanning to see the activity in different parts of the brain, all while performing neuropsychological tests.

In order to understand the dreaming state we must fundamentally realize that the dream self is different than the waking self – it is the product of a subset of brain systems functioning to produce awareness. Researchers at present distinguish three types of awareness: awareness of phenomena and events (that stuff is happening), awareness of the the mental state (called meta-awareness, basically the awareness that ourselves and others possess an internal mental state), and awareness of the self (that we exist and are conscious). While our waking selves have all three forms of awareness, current models suggest that our sleeping selves lack meta-awareness.

Another aspect of this is that meta-awareness seems to be a critical part of another brain function called reality-testing, in which we test our internal mental model of reality against external experience. So our reality testing is not functioning during dreaming – we are incapable of noticing that things in our dreams don’t make sense.

Yet another way to explain this is that reality testing serves also to distinguish external reality from ideas that arise within our brain. We can therefore distinguish what we imagine from what we experience. This process is not perfect, and our memories are especially vulnerable to failures of making this distinction. Delusions and hallucinations are also a manifestation of failing to distinguish ideas from external reality.

While we are dreaming the reality testing part of our brains, part of the frontal lobes, is not as active as when we are awake. Therefore our dreaming selves are incapable of noticing that the weird and bizarre stuff of dreams is not “real.”

I don’t know why, evolutionarily, this is how dreaming works. My suspicion is that because dreaming is mostly produced internally within the brain (although it may incorporate some external stimuli) there is no reason to reality test it. In fact, we know what happens when reality testing starts to function while dreaming – this produces a state called lucid dreaming. When a dream becomes lucid you know that you are dreaming, usually because your reality testing kicks in and you can tell that the dream is unreal.

While is is fun, and people have learned to increase the frequency with which they can enter the lucid state, it is inherently unstable. While lucid dreaming there is a tendency to either actually wake up or to dream that you wake up, in which case you no longer know you are dreaming.

This fits with the notion that we do not have reality testing while dreaming in order to make the dream state more stable – to keep us dreaming by preventing the dreaming self from realizing it is dreaming. (This reminds me of the Matrix – the computers that have enslaved the human race have made the Matrix as realistic as possible in order to keep people from realizing they are in a computer simulation. But a few people sense the unreality of the Matrix, they are unstable, and have to be removed from the Matrix.)

There may be other benefits as well, and I suspect dream researchers are and will be sorting this out. For example, lucid dreaming may not be as conducive to restorative sleep and full dreaming. There is evidence to suggest that dreaming serves to consolidate and reinforce memories from the previous day, and perhaps lucid dreaming does not serve this function as well.

Therefore, it is likely that we evolved so that while dreaming our reality testing is turned off, in order to make the dreaming state more stable and perhaps serve other functions. Alternatively, the lack of reality testing during dreaming may just be an epiphenomenon – not necessary, just a random consequence of evolution. Perhaps there is no advantage to having reality testing during sleep, even if there is no disadvantage. I tend to think that the former is true, however.

Getting back to the original question – why are dreams so weird, it is simply because the dream state lacks reality testing. There is a lack of reality testing during dreaming because it is not necessary and probably also because it is counterproductive. This can happen because reality testing is not inherent to brain function or the construction of consciousness. It is, rather, just one component of consciousness that can be localized to a specific part of the brain and can be selectively turned off, as it is during the dreaming state.