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Chakras are spiritual centers in a body, centers that join a  man with spiritual plains. And there are great spiritual powers.
In current westërn texts is strictly recommended meditate about all chakras. But, in eastern countrees are two ways. There about all chakras do a meditation only yogis, who want to awake the Serpent power, Kundalini and terminate the cycle of lifes, to that calculated lives in a spiritual worlds too.
Yogis who wish to obtain a supernatural powers, and another life in a spiritual worlds do meditation only on a one chakra. Mostly the chakra Anahata for a many years. Only this way awaken in the chakra hidden powers and powers of the lower chakras are then assigned themselves.
Several texts recomended concentartion about the chakra Ajna only. But, there is a great danger of self-destruction the yogi, who done it.

For the awakening the Anahata chakra may be used the follow the breath before a bedtime. Very accelerate the achievement of this.

Good books about Chakras are Shiva samita, Sat chakra nirupana and by A. Avalon, The serpent power.

A similar procedure is in Chinese Taoist alchemy, see you
The secret of the Golden flower. But there is chakra Ajna called "Heavenly Heart and Anahata "Fleshly heart".
The Secret of the Golden Flower   
There is a process of concentration of mind for about three months to Ajna chakra and then transfer the attention to chakra anahata with monitoring breath.

This way awake  powers hidden in the chakra.

See you also the path of Alchemy, for example "The book of Lambspring". (On Levity .com alchemy)
Figure III In the Body there is Soul and Spirit.

In the ancient spiritual teachings is the spirit between the eyebrows, Ajna chakra in yoga
and soul in the place of Anahata chakra.

All quoted texts are freely on the net in pdf format