Levels of Consciousness and Brain Activity

 When beginning to unravel the mystery of consciousness and all of its complex layers, it can be hard to know where to start.  Not only are there multiple levels of consciousness, but there are also different patterns of brain activity that correspond to each level.  In The Ravenous Brain, Daniel Bor explores this topic and attempts to navigate through the inevitable complexity of the subject by zeroing in on one aspect at a time.  His chapter "The Tip of the Iceberg" discusses how active our brains can be even when we are unconscious.

Source: Deric Bownds

When a patient is being prepped for an invasive surgery, typically they receive some sort of anesthetic.  The anesthetic makes us unconscious because it increases the production of the neurotransmitter GABA (gamma-amino-butyric acid) which puts a damper on neuronal activity throughout the brain.  When we are unconscious, the firing of our neurons becomes more uniform, meaning neurons fire together in a more slow and rhythmic pattern than usual.  What is interesting is that even though we are not conscious, our brain is still very active and neurons are firing in a bit of a stronger sense even though there is little information for the brain to attend to.  However, neurons in this state will struggle to communicate with neurons that are outside their immediate brain region since the brain isn't receiving any important information worthy of passing on.

Yeah...what he said.  Source: Freud-Sigmund.com

Since it is obviously important for a patient to actually be unconscious during surgery, it is helpful for doctors to be aware of these characteristic brain wave patterns.  Distinctive brain wave patterns also carry over to other levels of consciousness.  Marcello Massimini's team from the University of Milan discovered just this in a study of consciousness that used Transcranial Magnetic Stimulation.  They found that people in different states of consciousness did indeed respond to TMS with distinctive patterns of brain waves.  When the magnetic pulse activated a specific area of the brain, the team measured brain waves using EEG electrodes on the scalp.  To analyze EEG data, they created an algorithm called the "perturbational complexity index" or PCI that ranged from 0 to 1.  Basically they created a scale to measure the strength of the brain waves recorded by EEG.

The PCI was able to identify levels of consciousness in people with brain injuries.  For example, a patient who was in a vegetative state had a PCI score between .19 and .31.  This is the same score a healthy person would have if they were drugged or in deep sleep.  Similarly, a person who has normal thinking capabilities and full awareness, but cannot communicate with others because of total body paralysis have a PCI score of .51 to .62 which is the same as someone who is completely healthy.

What this study shows is that there is a lot that can be learned from studying the unconscious.  Even when one is unconscious, there is still a considerable amount of brain activity that goes on without us. Consciousness and related brain activity can be viewed on a spectrum that will never fully hit zero until after death. Our brains are always at work whether we are awake, asleep, day dreaming, or completely unconscious.  While this area of research is still in its early stages, Massimini's team hopes to gain further insight in to these patterns in hopes that it will help doctors treat people with brain injuries.

Source:  Hughes, Virginia. "Consciousness is a Process." National Geographic. N.p., 20 Aug. 2013. Web. 15 Oct. 2013. <http://phenomena.nationalgeographic.com/2013/08/20/consciousness-is-a-process/>.