The brain has always been the least understood human organ. Now researchers are busy building an atlas, or collection, of digitally mapped brains to find out what constitutes ``normal,'' Andrew Bridges reports Human brains are stunningly diverse. No two are identical, not even those of identical twins.

So when scientists are looking at a brain, how do they know when they're looking at one that's normal? It's hard not to recall the scene in the 1974 Mel Brooks comedy ``Young Frankenstein'' when Igor selects the ``Abby Normal'' brain for his boss to put in the monster. Researchers are now trying to better understand what constitutes a ``normal'' brain by studying a newly compiled atlas that contains digitally mapped images of 7,000 of the organs.

A decade in the making, the brain mapping project quietly debuted this summer. Use of the atlas allows researchers to compare and contrast these brain images, captured from all sorts of people living in seven nations on four continents. Most are between the ages of 20 and 40, but some are as young as 7 and as old as 90.

Along with the brain images of ``normal'' people are those of people suffering from Alzheimer's, fetal alcohol syndrome, autism and schizophrenia. More data are continually being added.

``This is a project born of frustration, basically. For many years, all of us who study brain structure and function have struggled with the fact that no two brains are the same -- not in shape or size and certainly not in function,'' said Dr John Mazziotta of the International Consortium for Brain Mapping, based at the University of California, Los Angeles.

``But how different they were and how to compare them was not known.'' His colleague, Dr Arthur Toga, says the plan is to quantify the differences between brains. Understanding the variations should provide ``a good index between normal populations and a diseased population."

This brain atlas -- freely available to registered users over the Internet -- maps the brains in multiple dimensions. It charts brain activity, pinpointing the seat of functions such as speech, memory, emotion and language and highlighting how those locations can vary among individuals and populations.

A researcher using this resource can call up any number of combinations of brains -- say, those of a group of left-handed, 20-year-old Asian women -- and compare them with another population to illustrate their similarities and differences. ``Might they be different from 90-year-old, left-handed men?'' Toga asked.

Findings from other types of comparisons also might lead in some surprising directions, Toga suggests, such as tweaking primary school curricula.

Some data suggest the brain is more receptive to learning some skills at certain stages of development, so it should be useful to map the growth of regions of the brain connected to specific skills. And since all of the brain images have been stretched, shrunken or otherwise manipulated to fit a standard reference, researchers can make apples-to-apples comparisons.

That sort of big-picture view gives clarity that individual snapshots cannot, said Michael J. Ackerman, of the US National Library of Medicine. ``When you're able to put it together and work with it, you begin to see things that weren't there when it was in individual pieces. That's the beauty of an amalgamated project,'' said Ackerman, who spearheaded the Visible Human Project, a digital atlas of detailed, three-dimensional representations of the human body.

Even so, drawing conclusions about the brain is very tricky. Individual differences may foil even the broadest efforts to generalize, said Stephen Hanson, of Rutgers University, who is not connected with the brain-mapping project. ``It's very hard to say, `that part of tissue is doing that, and that is not doing that.' Different tissues might be recruited at different times -- like Tinkertoys,'' said Hanson, co-director of the Rutgers Mind/Brain Analysis Center.

Toga, however, says the comparisons can tell a researcher where a certain structure or activity is most likely to occur -- even if the precise location varies from person to person. ``I have to use statistics to be sensitive to what clearly are very subtle differences,'' Toga said.

Researcher Arthur Toga at an interview at the University of California in Los Angeles. In the background is a digitally mapped image of a brain. Researchers are nearing completion of the world's first comprehensive atlas that lays out in map-form the function and structure of the normal adult human brain.

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