Well the Brain has gained over the long time more of volume, then the first such as called human. The Nature never has made such waist of material.
For example: In the beginning the human body has produced Vitamins. He was not on the top of the foot pyramid. Today he has almost no natural enemy's and he is not hunted to bee food of some other live forms. Today the human flesh contains near no Vitamin.
There mid be a significant different in active and passive use.
Consider this as close example:
From your main drive of the used space you can still not find all programs as active in you Task manager. It would most times exceed the the strength of the processor.
Here since the Disc material is not organic it needs no power (food) to survive.
If you close some at the moment not used task the speed of the rest remaining function increases.

By the human you call this focusing on something. (You ignore other influence of the environment).
In coma some times the brain starts to cut of to providing not need body parts. Effect is the lost of the oldest long times not used memories. Mussels.
The cells are still there and can be reanimated in a time window.

The passive part of the brain you can take as economy action of the body. He provides this part with only the need. Like you close the light in a unused store room. Yo switch on the light again, maybe also in the line of the shelfs. If you seek something there.
If the content of this sore room needs a special climate, you close by non use the light but not the acclimatisation.
Equal is you brain. If you want to remember you oldest child memory, you start to concentrate (putting the light on) to this time.
Passing marks floor X Shelf Y Nouveau Z... ( 5 years old, garden, withe ball.. a yea he had blue points, yea i remember i did hold him standing... i think the points where actually hexagons...) If you doe this often you train you memory part.
We store every signal we register through our senses. But we use not all.
You may have learned at school something and passed in a test very poor. On day you need exactly this in you life, you brain makes a recall. Then after a less or more active time, you may come to moments where you say >if i would known this at the test time at school i would have done better.< Well you did know this, just did not find it back on time you focus was not set to this point.

If you look the points of dreamed control you can find back, that all of them not already practiced by some few people.
Shaolin's throw needle's through glass without damaging the glass, there just ignore the existents of the glass (control of material)
Lay hands on people to heal them (control of cells)
Fake medicaments cell self control animation...

So if we use the hole capacity of our brain we need a bigger head to increase our capacity. (more space for the brain has caused in time machine the laying free along spinal column).

What most people really are interested in, is the use of need data which comports the life better any gives more independence.

How can you train this:
Train to seek solution, with increasing levels.
Train you imagination.
* Make you self pictures of you dreams.
* play games like what if
* play or doe reorganize you rooms
* draw things no matter how it looks like you have to know what it should show.

read and make mind maps, recall to read content, recall childhood times.
recall in playing what if....
recognize engineered problems and seek solutions
After a while you may even find solutions for energy problems...

Doe not cook only prepared food. THINK

play what is the next step (The Da Vinci Code).

biggest miss behavior of parents today is to give children only toys of TV series. They start to replay the movies without much imagination. give them Legos or somethings like. Animate them to engineer there played stories. If they are old enough don't give them a doll house or a garage for there  cars, give them Lego's and carton and colors. Work with them through the city to let them look buildings and ask them what they would like to have changed IF...
Sure at best is to seek out you child's talent and support those. If you are a ... what would you doe.

>Change you stars< (A Knight's Tale) You have to focus, on you vision.
You can't reach a point if you don't work on the route leading to this point.