Locating the brain's daily planner

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McGill Reporter
December 7, 2000 - Volume 33 Number 07
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Home > McGill Reporter > Volume 33: 2000-2001 > December 7, 2000 > Locating the brain's daily planner

Locating the brain's daily planner

Photo Psychology professor Michael Petrides
PHOTO: Claudio Calligaris

| There is a watchdog in your head.

Don't worry, it's not Big Brother. In fact, it's a part of your brain known as the pre-frontal cortex, the area directly behind your forehead. According to psychology professor Michael Petrides, this area is responsible for monitoring our own thoughts.

"The pre-frontal cortex is the best developed area of the brain in humans and in apes — less so in other animals," says Petrides.

"But its role in high cognitive processes has always been a mystery. Through our experiments using neuro-imaging technology, positron emission tomography (PET) and magnetic resonance imaging (MRI) we have pinpointed its contribution for the first time."

Specifically, the mid-dorsolateral region is in charge of keeping track of our thoughts and memories.

"We knew that patients with injuries to their pre-frontal cortex don't become amnesiacs. They still have their memories. But they have problems in planning and organizing their lives."

The ability to monitor thoughts is what makes planning and organization possible.

"Other parts of the brain hold our memories, the place where information and intentions are stored. The pre-frontal cortex allows us to look into the contents of our memories and thoughts, and to keep track of what's happening in our own mental world.

"Someone with damage to this area can tell you what they had to do today, yet they didn't do them, or they failed to do them efficiently. They have lost the capacity to keep track of their mental checklist, and to plan and organize accordingly."

Petrides believes that the pre-frontal cortex evolved late in humans and primates, perhaps as a result of increasingly mental demands from a more complex world.

"This area of the brain is critical for multitasking, juggling many tasks simultaneously, which we all do in our daily lives."

Beyond practical matters such as these, the pre-frontal cortex also allows the most profound forms of cognitive behaviour.

"We are discovering the neural basis of our highest forms of thought, our capacity to introspect, to think about our own thinking. Until now, it was more difficult to put your finger on the origin of these processes. They belonged more to the realm of philosophy than of science."

The ability to examine one's own thinking includes an element of self-policing.

"One of the big problems of patients with pre-frontal lesions is an inflexibility of behaviour and thinking; they have lost a system which gives constant feedback on our thinking processes. The feedback, and the emotional responses to this information, prompts us to change or modify our thinking patterns, according to our values and intentions."

Petrides started to study the pre-frontal cortex in the 1980s. He discovered that another area, the posterior dorsolateral region, is responsible for behaviour and thought processes which depend on conditional rules; for example, what to do when the traffic light is green, yellow or red.

The recent winner of the $600,000 James S. McDonnell 21st Century Scientist award, Petrides is now studying the ventrolateral region. He believes that this part of the pre-frontal cortex is involved in judgement and decision making using information stored in the posterior cortical area of the brain. He hopes to be able to map out the interactions between these various regions.

"Once we have identified their individual roles, the goal is to show how these regions of the pre-frontal cortex work together, and with the rest of the brain. Together, they provide a very powerful way of regulating our own actions, emotions and mental activity.

"There is still a lot of work to be done, but at least we have made a good beginning."

Petrides presented his findings in a lecture at Harvard University last week. The November issue of Nature Reviews Neuroscience featured an article on his work.

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