The Mind-Brain Connection

Coma provides a powerful example of the relationship between mind and brain.  There is a remarkable piece of neural circuitry located in your brain stem that functions a bit like an engine for your brain, pumping out energy that determines your level of alertness.  The engine that controls the frequency of brain waves is called the ascending reticular activating system (ARAS). When you are wide awake and engaged in a mentally challenging activity that demands intense concentration and high-level reasoning, then the ARAS pumps out very high frequency waves.  If we were to couple you to an EEG machine at that moment and measure your brain wave activity, we would find that the dominant brain wave forms are so-called gamma waves that range from about 40 Hz to about 100 Hz.

brain waves

When you are awake but not doing anything mentally demanding, then brain waves cycle at between about 14 Hz to 40 Hz, so-called beta waves.  As you relax, the ARAS slows down the frequency to between about 8Hz to 12Hz; alpha waves.  If you nod off and fall asleep, then the ARAS puts out theta waves, which oscillate between about 4 Hz to 8 Hz.

The slowest brain waves are delta waves, which range from about 0.5 Hz to about 4 Hz, and which in normal circumstances are found in infants and young children.  In abnormal circumstances, delta waves are found in comatose patients, and it usually means that the ARAS has been damaged.

The ultimate demonstration of the relationship between brain and mind is when the EEG no longer registers brain wave activity.  This is a major criterion for making a diagnosis of brain death.  In a comatose state, you effectively lose your mind and have no awareness of anything around you.  Damage to the ARAS effectively damages the mind.  Deeply comatose patients are mindless.  As mental activity returns and the patient begins to emerge from coma, so the ARAS begins working normally again.

Thus, the mind depends on the functioning of the brain.  When the brain malfunctions, so does the mind.  At the extreme, severe brain damage equates to complete absence of mind, and the absence of EEG activity is defined as brain death.



The amazing thing about your brain is that you can sit there and read these words and extract meaning from them.  You can take the neural code that I’ve slipped into your mind, think about it, and reach a conclusion.  No other animal can do that, only us, only homo sapiens.  Language, symbolic reasoning, sets us apart.