The Ultimate Test

The Ultimate Test is the sixth chapter of “Consciousness and the Brain:  Deciphering How the Brain Codes our Thoughts” is an outstanding book by the French neuroscientist Stanislas Dehaene who is the Chair of Experimental Psychology at the College of France.  This is the seventh consecutive post on this outstanding book. According to Dr. Dehaene the ultimate test of any theory of consciousness is the clinic.  Every year thousands of patients fall into a coma.  Unfortunately, many of these patients will remain permanently unresponsive in a dreaded condition called the “vegetative state.”  Worse yet, is that in Intensive Care Units (ICUs) over all the world, half of the deaths result from a clinical decision to remove life support.  How many of these decisions are wrongly made?

Coma is defined  clinically as a prolonged  loss of the capacity to be aroused.  However, coma patients are not brain-dead.  Brain death is a distinct state,characterized by a total absence of brain stem reflexes.  In brain-dead patients, positron emission tomography (PET) and other measures such as Doppler ultrasonography show that cortical metabolism and the perfusion of blood to the brain are annihilated.  Most countries, the Vatican included, identity brain death with death, period.

What is of primary interest is the “locked-in syndrome.”  This state typically results from a well-delimited lesion, usually on the protuberance of the brain stem.  Such a lesion disconnects the cortex the cortex from its output pathways  in the spinal cord.  If the cortex and the thalamus are spared, it often leaves consciousness intact.  As you can well imagine, this is a terrible state in which to find oneself.

The book “The Diving Bell and the Butterfly” (there is also an outstanding movie by the same name) was written by Jean-Dominique Baby, who was the editor of the French fashion magazine, “Elle.”  He wrote this book one character at a time by blinking his left eyelid while an assistant recited the letters of the alphabet.  He eloquently told his story with two hundred thousand blinks telling the story of a beautiful mind shattered by a cerebral stroke.  Fortunately he lived to se the book published, but, unfortunately, he died three days later.

Comparatively speaking, Jean-Domonique Baby was well-off. Many locked-in patients have no motor responses, no means of communicating with the world.  Fortunately fMRIs can identify these individuals, given enough time.  Unfortunately, fMRIs are extremely expensive and are beyond the budgets of too many medical facilities.  But, fortunately, Dr. Dehaene has developed an inexpensive test using EEG recordings using 256 electrodes.  Information exchanged over long cortical distances is an excellent index of consciousness in patients with brain lesions.  Computations are done for each pair of electrodes for a mathematical index of the amount of information shared by the underlying brain areas.  Vegetative-state patients showed a much smaller  amount of shared information than conscious patients and control patients.  This finding fits with  with a central tenet of global workspace theory, that information exchange is an essential function of consciousness.  A follow-up study showed that the few vegetative patients who showed high information sharing had a better chance of regaining consciousness within the next days or  months.

So technology and the global workspace theory provide good diagnostic techniques.  It is hoped that interventions will be developed in the future to unlock those in a locked-in state.  Dr. Dehaene has described some promising work being done in this area.


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