Aliens can restore brain power by two different ways. Either by being told to restore brain power, where they will then do this weird sound and I think have their hands out and their brain powers will start to refill.
The second way, which I have used when they need a quick boost, or can't go and sit somewhere to restore brain power, is to consume space rocks. I keep four or five in my sims inventory to have when they get low on brain power and need a quick boost. I can't remember if they have to sit to restore their brain power, but I had them go and sit somewhere away from others as they refilled their brain powers.
In breaking space rocks, when your sim has reached a high enough rank in board breaking they can break open what is called space rocks. They look just like a board but are made of space rocks. In doing so they can find all kinds of gems, many which are the ones that can be hard to find elsewhere. I had tiberium, soulpeace, pink diamonds and many other gems show up when my sims were breaking space rocks.
