A recent study reveals that when we focus on searching for something, regions across the brain are pulled into the search. The study sheds light on how attention works.
In the experiments, brain activity was recorded as participants searched for people or vehicles in movie clips. Computational models showed how each of the roughly 50,000 locations near the cortex responded to each of the 935 categories of objects and actions seen in the movie clips.
When participants searched for humans, relatively more of the cortex was devoted to humans, and when they searched for vehicles, more of the cortex was devoted to vehicles.
Now this might not sound very surprising, but it appears to contradict our whole developing picture of the brain as having specialized areas for specific categories — instead, areas normally involved in recognizing categories such as plants or buildings were being switched to become attuned to humans or vehicles. The changes occurred across the brain, not just in those regions devoted to vision, and in fact, the largest changes were seen in the prefrontal cortex.
What this suggests is that categories are represented in highly organized, continuous maps, a ‘semantic space’, as it were. By increasing the representation of the target category (and related categories) at the expense of other categories, this semantic space is changed. Note that this did not come about in response to the detection of the target; it occurred in response to the direction of attention — the goal setting.
In other words, in the same way that gravity warps the space-time continuum (well, probably not the exact same way!), attention warps your mental continuum.
You can play with an interactive online brain viewer which tries to portray this semantic space.
 Attention during natural vision warps semantic representation across the human brain. Nature Neuroscience. advance online publication,(2013).