Everyday actions such as sending an email or eating a sandwich are governed in the brain by a cascade of decision-making that runs from abstract to concrete, rather as in a large corporation, a new study has shown.
The process takes place along a path moving from front to back in a key region in the brain called the prefrontal cortex, located just behind the forehead.
"It is among the strongest evidence to date for a systemic organization of the frontal cortex," said lead author David Badre of Brown University in Providence, Rhode Island.
When tissue somewhere along this trajectory is damaged, only the abstract decisions -- choosing the sandwich, for example -- are impaired, leaving the more mechanical task of actually bringing the food to one's mouth unaffected, the study found.
Earlier research had shown that the prefrontal cortex handles so-called "executive functions" such as sorting out conflicting thoughts, achieving goals, and exercising social control over sexual and emotional urges.
It controls the capacity to plan, reason, conduct higher-level thinking and connect what we know about the world to how we behave.
But how the information pouring in from all the senses is hierarchically organised -- or whether there is any hierarchy at all -- has been hotly debated among neuroscientists.
The new study adds weight to theories pointing to a flow of decision-making within the prefrontal cortex in which abstract trumps concrete.
"It is like a hierarchy in a company. The CEO (chief executive officer) can direct the people directly below him, or all the way down to the lowest levels," Badre explained by phone.
"But the person in the mail room can't direct the CEO, so there is an asymmetry of influence."
Badre and colleagues arrived at these conclusions by studying 11 stroke victims who suffered damage to different parts of the frontal lobe.
The patients were given a series of four tests that required progressively greater degrees of complexity and abstract thinking. The location of their lesions along the abstract-to-concrete axis in the frontal lobe corresponded to how well they performed.
"If you take out the middle manager" -- the equivalent of damaged brain tissue -- "the people in the mailroom can still operate," Badre said, extending the metaphor.
"But if they need direction from up above they can no longer be directed."
The findings, published online Sunday in the journal Nature Neuroscience, fill in an important piece of the puzzle of how this part of the brain directly human behaviour, and could also lead to new treatments for stroke victims, Badre said.