MadSci Network: Neuroscience

Re: When a person is in a coma, do they have brain waves?

Date: Fri Apr 21 08:36:59 2000
Posted By: James Goss, Post-doc/Fellow, Neurology, University of Pittsburgh
Area of science: Neuroscience
ID: 954953648.Ns

   The simple answer to your question is yes, people in comas have brain 
waves.  But, this does not mean that they are only 'asleep'.  The 
measurement of brain waves (called electroencephalography or EEG) can show 
the activity level of the brain.  When people are awake they display 
certain types of brain waves that are characteristic of high activity.  
During sleep, these same high activity brain waves can still be recorded, 
especially when the person is dreaming.  
   A coma is a condition that is behaviorally and physiologically different 
from sleep.  A person in a coma is unconscious and not able to be awakened. 
 This differs from sleep, because you can easily wake up someone who is 
asleep.  Coma and sleep also differ in the amount of blood that flows into 
the brain (blood carries oxygen and the brain needs more oxygen than any 
other organ in the body).  During sleep, the blood flow in the brain is the 
same or higher than when the person is awake.  However, in a coma, the 
blood flow is always lower.  The brain waves, or EEGs, of coma patients are 
also different from patients who are awake or sleeping, but not all coma 
patients have the same EEG patterns.  Doctors can often tell what part of 
the brain was injured and thus tell what caused a coma by looking at EEGs. 
 Additionally, there are different levels of coma.  While you cannot 'wake 
up' a person in a coma, some coma patients can respond to some stimuli.  
For example, some patient's EEGs show a reaction when a loud noise is made 
near the ear.  Other patients in coma show absolutely no reaction to any 
stimuli.  Once a person has no brain waves, that person is said to be 
'brain dead'.
   Hope this answered your question.

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