Electroencephalograph (EEG)

The EEG measures electrical activity of the brain using pairs of electrodes placed at different (internationally specified) points on the scalp. It is used by doctors for diagnosis and research.

It seemed that the EEG would provide the key to understanding how the brain functions, but it proved very difficult to interpret these brain waves, or to deduce from where in the brain they originated.

Magnetoencephalograph (MEG)

The MEG, however, can measure

the oscillating millisecond fluxes of the brain in real time. Furthermore, unlike the EEG, granted enough mathematical sophistication and computing power, you get a good idea of the location of the electromagnetic source in the brain.

And it can be used to

record magnetic and electrical fields within the brain simultaneously, tracking impulses moving (a distance of) a few millimetres at up to 200 miles per hour.

In real time, that is 'in perhaps 10 milliseconds'. And 'usually accurate to within one or two millimetres in pre-surgical mapping'.

And in this way enabling responses to be tracked within the brain.

The brain functions by sending electrical signals from one place to another. Very small charges pass between nerve cells, accompanied by changes in electrical potential, in voltage.

This activity can be measured and displayed as a wave form called brain wave or brain rhythm. The height of the wave is a measure of the potential difference, its frequency is a measure of the rate at which electrical charges pass through a nerve cell or nerve fibre.

A person's brain is active all the time, waking and sleeping, producing and shifting between distinct wave forms which are commonly grouped as follows:

Table 1

Brain Waves

When delta waves predominate then one is said to be in a delta state.

People can think of relaxing and so strengthen alpha waves, or can do mental arithmetic and so weaken them. This enables people 'to perform an on-off decision, switching a light on or off or moving a cursor on a screen'.