by John Cowley

Created on: August 24, 2008   Last Updated: August 28, 2008

When discussing this question it can be quite misleading to assume that the brain is entirely under our volitional control. In fact many parts of the human brain, such as the cerebellum, the mid brain and the pons, control essential bodily functions such as breathing and other semi automated functions which we are mostly unaware of. What most people are possibly hinting at, in suggesting that we only use ten per cent of our brain, is the role of the cerebrum and its conscious control over our actions. Then again, some psychologists would maintain that the feeling of being in control is an illusion, a way of rationalizing our actions after the event.

Depending on whether we are sleeping, or we are awake and in various levels of activity, we use an ever increasing percentage of our brain which is generally in excess of ten per cent. By way of an analogy we can compare the brain to a generator which is always working to maintain power to our electrical circuits. Degrees of mental activity can be compared to the numbers of lights which are switched on to tap into the generated electrical current. Switching off all the lights still leaves the generator humming away maintaining the power potential. The use of an electroencephalograph, EEG, can actually measure this background hum in the brain.

Perhaps the question ought to be rephrased to relate to what percentage of conscious control we have over activities primarily controlled by the cerebrum. It could be argued that when we are asleep we must be using hardly any of the cerebrum's capacity. However magnetic resonance imaging, MRI, research would tend to contradict this argument, demonstrating that there is a veritable hive of activity taking place even during so-called unconscious states. Some researchers would maintain that we are never truly not conscious as long as we are alive in the sense that we are not brain dead.

In order to understand more fully the role of the cerebrum in conscious activities such as thinking and decision making we need to examine these processes in greater detail. Techniques such as MRI and PET, positron emission topography, reveal extensive downward projections from cortex to thalamus. A consensus view has emerged in which reverberatory feedback between the thalamus and pyramidal cells in the cortex are thought to provide the neural correlate of consciousness. Electrophysiological recordings, EEG, demonstrate coherent firing of thalamo-cortical loops with frequencies from slow EEG frequencies

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