The Brow Chakra
The Brow chakra is thought to be sited in the centre of the forehead, immediately between the eyes, but back into the head. Its usually associated colour is indigo. People sometimes call this centre the third eye, and suggest that the sixth sense comes from here (actually it's interesting how many godforms are described as having only one eye in the centre of the forehead through which they see everything).
This chakra deals with our psychic abilities, which flow through here and into the mind. It also covers the function of the subconscious and unconscious minds.
In addition to these functions, it also provides our objectivity when analysing complex issues, our ability to integrate philosophical material, and develop belief systems. So it's a little like a metaphysical filter.
Physically it controls sight, all frontal lobe brain functions, hearing (with the throat centre) olfactory organs, and some of our ability to speak (again with the throat). Memory, the ability to create mental images, and the ability to connect one concept or idea with another all flow from here.
If function is poor sleeplessness, headaches, confusion, vision disturbance, concentration, and memory will all be affected. When this centre doesn't function healthily we lose our ability to intuit, becoming wooly-headed. we will be unable to think ideas through clearly and come to conclusions. Our ethical integrity may be undermined. In really severe cases we will become delusional.
This centre is quite vulnerable to external influences, and should not be left running full powered for long periods of time, because you will find yourself absorbing unhealthy and unwelcome influences. This is one reason why people are always told to close down contact after meditations and so on.
It's also a good idea to develop a good method of shielding the centre - by imaging something that satisfactorily 'semi-closes' the chakra. Don't close it all the way down though, unless you feel endangered - that'll give you a headache!!!