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The Conscious Brain

10/29/17

When people are not conscious, e.g. those in a vegetative state, their brains show very low levels of neuronal activity.  Their neurons may occasionally respond to stimuli, say a loud sound, but not many neurons, and not for very long.

Those in a minimally conscious state, with only occasional periods of awareness, show somewhat higher and more sustained levels of brain activity.

When we are fully conscious, the things we see, think, remember, and our other conscious experiences, are accompanied by strong activation of the neurons in the brain.


So there’s a relationship between conscious awareness and the activity of brain cells.    As I write this post, I’m picturing a brain.  To do this, I'm activating certain neurons in visual areas of my brain that give rise to the mental image.

But not all neuronal activity gives rise to consciousness. Some neurons, for instance, become active just before you grasp a cup, and determine the position for you to place your fingers as you move your hand toward it. If your grasp is wide, these brain areas will quickly send updated commands to your hand muscles so that you grasp the cup in a way that allows you to lift it, and not drop it. Next time you grab for a similar-sized cup, your brain may instruct your hand muscles to produce this 'narrower' grasp. Lots of neurons in several areas of your brain are activated in order to adjust your hand position, and usually this activity falls outside your awareness. The neurons are activated but they don’t give rise to a conscious experience of adjusting your hand position.

What is the difference between the neuronal activity that gives rise to conscious awareness and the neuronal activity that doesn't.
  • Maybe it depends on the part of the brain that's activated.  There may be some brain areas where neuronal activity is off-limits to conscious awareness. You might imagine these areas to include those that control aspects of body movement; habitual, automatized behaviors; and the kinds of thoughts and goals that Freud envisioned residing within the unconscious.
  • Maybe most of the neurons in the brain are off-limits to consciousness. It could be that conscious experiences are made up of the neuronal signals that transmit information to a privileged brain region, a kind of 'seat of consciousness'.  This area (which some neuroscientists imagine to be in the frontal cortex) would be the stage upon which the drama of our inner-lives (the hopes, plans, memories, regrets, and so on) unfold. 
  • Maybe any of my 100-billion-or-so neurons can contribute to a conscious experience -- so long as the neurons fire rapidly enough, or so long as their activity is synchronized with the activity of enough other neurons in the brain.
There are many other 'maybes' about how neural activity could relate to consciousness. But whichever explanations turn out to be true, the nagging and interesting questions would remain: "Why should neurons in those brain areas, and not others, give rise to a conscious experience?" "What's so special about brain area X that I'm only conscious of inputs to that area?" "Why do neurons have to fire at a certain rate, or in a certain rhythm with respect to other neurons, in order to produce a conscious sensation?"