A study, published in the November issue of the international Journal of Cognitive Neuroscience, has shown that it is possible for researchers to look at brain imaging data and determine whether a person is imagining a face or a place.

"With the technology available to us today, we are now able to identify the content of a person's thought, albeit in a very limited context," says Dr. Kathleen O'Craven, a cognitive neuroscientist who led the study at Massachusetts General Hospital. Dr. O'Craven is now with Toronto's Rotman Research Institute at Baycrest Centre for Geriatric Care.

In the study, six women and two men, aged 20 to 39, were put through two cognitive exercises: one involved looking at pictures of faces, and a second involved looking at pictures of places or landscapes. Later these same adults were asked to mentally 'imagine' the faces and the places they had earlier seen. During both tests, functional magnetic resonance imaging (fMRI) scans were taken of their brains.

Many previous studies have shown that brain areas can be selective for processing a particular type of visual information. In the cortical brain regions associated with mental processing, the 'fusiform' face area responds strongly to faces while the 'parahippocampal' place area responds strongly to indoor and outdoor scenes depicting the layout of local space.

In this study, Dr. O'Craven and colleague Dr. Nancy Kanwisher of the Massachusetts Institute of Technology found the strongest evidence yet that this specialization holds true even when participants were given no visual stimulus and were simply asked to 'imagine' a face or a place. They also found that the magnitude of activity in these two brain areas is much livelier or stronger when one is seeing the picture (physically present in front of them) compared with just imagining it.

The most fascinating finding, however, is when 'data coders' (researchers who interpret data) were asked to look at fMRI scans and guess whether the study participant was thinking of a face or place. They were able to accurately report what the participant was thinking about on 85 percent of the trials!

"What we've shown is that we can actually tell, on a moment-by-moment basis, what an individual is thinking about, by measuring brain activity rather than having the person tell us," says Dr. O'Craven. "Of course, this can be done only in a limited context -- we've been able to demonstrate it for differentiating between faces and places -- but the implications are far-reaching."

She says the technique could be used to gain some insight into what is happening in the minds of people who are unable to communicate because they are suffering from an injury or disorder that makes speech impossible.

"We may someday be able to get a glimpse of what a patient is able to comprehend, even when that person can't answer questions directly. We could show them pictures of faces and places and, using fMRI technology, see whether their visual system is processing them. In addition, if these brain areas respond differentially to the 'spoken' names of people and places, we may be able to infer that they understand."

The study was supported by The Bunting Institute at Radcliffe College and by grants from the National Institute of Mental Health, the Human Frontiers Science Program, and the Dana Foundation.

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