This is driven entirely by proximal input. Each minicolumn has a receptive field, or viewport of the input space. If enough bits in that space are on at any given time step, the minicolumn will become active, always in response to changing spatial proximal input over time.
A minicolumn might go without becoming active if by chance there is just not much spatial input within its receptive field, but we try to encourage minicolumns to represent more patterns with boosting:
