Brain Functioning (by David F. Salisbury)

Different parts of the brain handle fantasy and reality

By David F. Salisbury

March 28, 2002

The ability to recognize objects in the real world is handled by different parts of the brain than those that allow us to imagine what the world is like. That is the result of a brain mapping experiment published in the March 28 issue of the journal Neuron.

The study focused on two cognitive tasks widely used by experimental psychologists. One is mental rotation – mentally a rotating a complex object into a different position to compare it with a second similar shape – and object recognition – determining whether two complex objects are the same or different.

"Mental rotation and object recognition are indistinguishable from a behavioral viewpoint: You can't tell them apart," says the paper's first author, Isabel Gauthier, assistant professor of psychology at Vanderbilt. "As a result, the field has been deadlocked over the question of whether the brain uses the same mechanism and different mechanisms for the two tasks."

Michael J. Tarr, one of the paper's co-authors and professor of cognitive and linguistic sciences at Brown University, had proposed in several papers with Steven Pinker at the Massachusetts Institute of Technology that the same mechanism must be involved in the two tasks. "There are parts of our brain that are involved in our ability to imagine the world," he says. "The question is, ‘Are those the same as the parts of the brain that we use to know what things are?' And the answer appears to be, ‘No, they are not.'

Also collaborating on the study were William G. Hayward of Chinese University of Hong Kong and an fMRI team from the Yale School of Medicine headed by John C. Gore.

To find out what parts of the brain are involved in these two mental tasks, the researchers began with six unfamiliar geometric shapes that look something like the pieces from an unfolded Rubic's cube. They used three of these objects – two of which were mirror images – for the mental rotation tasks and three which were slightly different but similar in appearance for the object recognition tasks. Next, they assembled a group of 15 subjects and used functional Magnetic Resonance Imaging machine to measure activity levels in different parts of their brains.

During the fMRI sessions, the researchers had the subjects perform two types of tasks using the objects. They displayed the objects in pairs on a screen and, in one case, they asked the subjects whether the two are identical or mirror images – a basic mental rotation task. In the other case, they asked them whether the two objects were the same or different – a basic object recognition task. The objects were shown at different angles from each other on the horizontal, vertical and out-of-plane