Jul 30 2012
Where is the “seat of consciousness” in the brain? This is often presented as an enduring mystery of modern neuroscience, and to an extent it is. It is a very complex question and we don’t yet have anything like a complete answer, or even a consensus. The question itself may contain false assumptions – what, exactly, is consciousness, and perhaps what we call consciousness emerges from the collective activity of the entire brain, not a subset. Perhaps every network in the brain is conscious to some degree, and what we experience as our consciousness is the aggregate effect of many little consciousnesses.
One way to approach this question (really a set of related questions) is to study different mental states – altered states of consciousness. How those differences relate to brain function are likely to tell us something about the contribution of that brain function to full wakeful consciousness.
A new study by scientists from the Max Planck Institutes of Psychiatry in Munich and for Human Cognitive and Brain Sciences in Leipzig and from Charité in Berlin attempts to do just that. They have studied the brain activity of those in normal dreaming and in a so-called lucid dreaming state.
Dreaming is an excellent subject of study for questions of consciousness. I often use dreaming when discussing this topic as an example of an altered state that everyone experiences. While dreaming we have awareness and experience and are forming memories (at least sometimes). When we remember our dreams, however, they don’t quite make sense to our waking selves. Things happen in dreams, for example, that are clearly impossible and yet that does not seem to bother our dreaming self. We are not aware that we are dreaming, despite the weird and dream-like events that are happening. Our dreaming self also just knows things about the context of the dream without the need for that information to be communicated – since the dream world exists entirely within our own brains there is no real distinction between ourself and the world.
At times, however, a dreamer can become “lucid” – meaning they become aware that they are dreaming. They notice the unreal aspect of the dreamworld. Some people can train themselves to have frequent lucid dreams, and to have a high degree of control of the lucid dream. The lucid dreaming state, however, is inherently unstable. We tend to either wake up, or dream that we wake up, which means losing the lucid state.
There are therefore three different states of consciousness that researchers can safely and reproducibly use to study consciousness – waking, dreaming, and lucid dreaming. What the researchers in the current study found was this:
“The general basic activity of the brain is similar in a normal dream and in a lucid dream,” says Michael Czisch, head of a research group at the Max Planck Institute of Psychiatry. “In a lucid state, however, the activity in certain areas of the cerebral cortex increases markedly within seconds. The involved areas of the cerebral cortex are the right dorsolateral prefrontal cortex, to which commonly the function of self-assessment is attributed, and the frontopolar regions, which are responsible for evaluating our own thoughts and feelings. The precuneus is also especially active, a part of the brain that has long been linked with self-perception.”
This study, therefore, supports the idea that a key difference between the wakeful and dreaming state is the lack of self-assessment in the dreaming state. The dorsolateral prefontal cortex is involved with decision-making, memories that are personally meaningful, and other aspects of self-assessment. The frontopolar regions are also involved with planning, maintaining a primary goal, and multitasking.
One thing that surprises me (a bit) about this study is that reality-monitoring was not directly implicated. Reality-monitoring is related to self-assessment – it is the ability to distinguish a memory from an active experience, or something imagined from something that actually happened. It seems that this is impaired in the dreaming state – we are not aware that we are dreaming, and we cannot distinguish imagined memories that are part of the narrative of the dream from actual memories of real events. This process also localizes to the prefrontal cortex (the anteromedial PFC) – so perhaps it’s close enough for fMRI.
Also (and here is why reverse-engineering brain function is so complex) perhaps the activity in the brain regions identified in this study affect the function of reality monitoring. The brain does not appear to be comprised simply of discrete modules that function all by themselves, but networks of modules all interacting with each other. Change the activity of one brain region or network and you will alter the function of other related networks. Perhaps simply looking at the amount of activity in different brain regions is giving us a very incomplete picture.
The study of the wakeful, dreaming, and lucid dreaming states appears to be a fruitful avenue for addressing questions of consciousness. Of course, it is just one approach to a very complex question. Such questions are best addressed scientifically from multiple angles and perspectives. This and similar research, however, is all premised on the theory that consciousness (whatever it is) emerges from brain activity. We are beginning to piece together the various contributions to consciousness of the various networks and modules in the brain. This kind of research will take us very far, but I think in order to fully understand this process we will need to model consciousness. When we have something like a virtual brain running inside a computer, where we can turn on and off different components at will to see how it affects the behavior of the system, we will have another powerful tool for addressing this question. Of course, we will never know what the system actually experiences – only how it behaves and what it tells us it experiences. But the same is true of human research.
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