How Brain Mapping Works

Scientists use many methods to study the brain's structure and function. They take pictures of healthy brains and compare them to diseased brains. In addition, they examine brains taken from humans,primatesand small mammals and try to understand how invertebrates' smaller nervous systems work. On a microscopic level, they also examine neurons.

Here are some tools used in brain mapping. These techniques take images of the brain:

These techniques examine brain activity:

New methods allow researchers to see all the connections between neurons in an intact brain. This branch of study is calledconnectomics.The "wiring diagram" of a brain is called aconnectome[source:Lichtman]. "Until recently, we've had no hope of getting these wiring diagrams," says Jeff Lichtman, a Harvard biologist who led the group that developed some of the new techniques. "We could see individual cells, but never all of them at once."

One such technique, known asBrainbow, labels every neuron in a live animal's brain a different color. By generating images of the animal's brain, scientists can see where and how neurons connect to each other. As the animal grows and ages, they can also watch how the neurons change connections.

Another technique uses theATLUM,orautomatic tape-collecting lathe ultramicrotome. This machine reads the wiring diagram of a brain. "We do something akin to paring an apple," explains Lichtman. "We essentially shave off a spiral cut as we rotate the brain on a lathe and put this ribbon of tissue onto a tape. We'll eventually get a hugely long tape, which is essentially the whole brain. Using anelectron microscope, we will image that to see the structure of the wiring."

So far, Brainbow and the ATLUM are being used only to study animals with relatively small brains, like mice.

So, what's the point? What, if anything, can mapping accomplish? Learn what we can learn from mapping the human brain on the next page.

Why would scientists take on the arduous task of brain mapping? The answer is simple, says Lichtman: to understand our brains more intimately. We have never seen a diagram of how all of the neurons in the brain connect. As Jeff Lichtman puts it, "A lot of our thinking about the brain is based on incomplete knowledge of what is actually there. So we would like to see what is actually there."

The brain's wiring diagram may help us better understand how we learn and adapt, says Lichtman. "We start out being less well adapted to our environment than any other animal. By the time we're adults, we can use tools that our genetic heritage couldn't possibly have taught our nervous system to use -- like iPods. No other animal can do that. During our development, we must wire ourselves to [be able to] use these machines."

Brain mapping is also of practical use to doctors. Neurosurgeons use brain mapping to plan safer surgeries. One treatment for epilepsy, for example, removes the affected part of the brain. Using functional MRI and EEG, surgeons can locate the seizure center in a patient's brain -- as well as areas that are active during speaking and moving -- down to the millimeter. These images tell doctors what to leave and what to cut out.

Brain imaging is not only used in treatment. It is used to diagnose neurodegenerative diseases like Parkinson's and Alzheimer's [source: Wilson]. Using tagging techniques like PET, doctors look for drops in certain brain chemicals, or they may use MRI to examine shrinkages in areas show tissue loss. Over time, doctors can map what the brain looks like as diseases progress or as treatments work [source:Institute for Neurodegenerative Disorders].

Developmental disorders likeautismmay have a structural basis in the brain. Lichtman points out that autism is thought to involve a series of wrong connections between neurons. By applying Brainbow to a mouse with autism, researchers might see the wiring diagram evolve to find out how, when and if the wiring goes wrong.

Scientists have also sought to illustrate the effects of various mental illnesses in the brain, with some success. Brain imaging on these patients revealed structural abnormalities. For example, structural MRI has shown thatschizophrenicpatients lose matter in thetemporalandprefrontal cortexover time [Source:Rapoport]. These findings have yet to lead to treatments.

Panic disorder,bipolar disorder,depression, anxiety, eating disorders and more are being examined using different brain imaging techniques, but how do we interpret scientists' findings? More importantly, where can we see them? Find out on the next page.

Neuroinformatics places all the data we have on the brain on theInternetin usable form. The data include images, models of neuron behavior and maps of thegenesthat are "turned on" in different brain regions. By making the data sharable and searchable, brain researchers can piggyback off of one another's studies and discover more.

Engineers are writing software to help brain researchers share and compare data. Software now analyzes, for instance, whether MRIs of Alzheimer's patients with different brain sizes and shapes have similar brain features. Are men with a certain brain architecture predisposed to bipolar disorder? This question, and many others, may one day be answered by computer programs that re-analyze images of past patients rather than by studying new ones.

Here are examples of brain atlases that researchers can mine for answers:

Images aren't the only source of information. Here are examples of databases brain researchers use:

Now that we can map the human brain, how far have we gotten? Are we done yet? Are we even close? Find out on the next page.

After imaging the brains of populations large enough to generate statistics, researchers have made sophisticated brain maps. There are maps to illustrate where we lose brain volume as we age, as AIDS progresses and as we use methamphetamines.

What would a complete map of the human brain look like? That depends on your interests. If you thirst to know the brain's structure, you might want to see that hypothetical Google Earth version that can begin with a picture of our cortex and zoom in to neuron number 888,898,432,857.

这个完整的,谷歌地球的地图是停滞不前at many points. One such point is the imaging of all of the human brain's neurons and their connections. Even getting this data in the mouse is painstaking, says Harvard biologist Jeff Lichtman. At the rate theATLUMand an electron microscope are now working, getting a map of all the interconnected neurons in the mouse brain would take 200,000 weeks, Lichtman estimates. The data would be "bigger than all the data on the Internet -- bigger than all the data in all the libraries in the world," he says. "At the moment, the kind of storage that's possible on computers is not quite up to task." The only "brain" for which we have a complete map of interconnecting neurons belongs toC. elegans, "a worm that's a millimeter long and has 300nervecells," says Lichtman.

Again, your definition of a complete brain map depends on your interests. If you're a neuropsychiatrist, for example, a complete map of the brain might be a time-lapse image showing how bipolar disorder unfolds in the brain from birth to the first symptom and what lithium does to stop the process.

That might not be enough for you. You might want to know the function of the brain's every last inch. Unfortunately, that's impossible. We can't capture functions that happen too quickly or too slowly, says neurobiologist Charles Wilson. Other processes take a lifetime. No imaging study has followed someone frombirthtodeath. "No method that we know of handles every time of interest. No method we know of handles more than a tiny piece of it," says Wilson. At this point, Lichtman says there is no current effort underway to integrate all of these maps into one.

But there's no fundamental reason why we can't eventually have any - or all -- of these maps, says Wilson. "The problems are all practical technology problems that can be overcome. As with any map, if you start with a crude map, it's better than no map. And you don't need a new map. You just add information to the old map to make it more refined. We aren't going to wake up one day and have this. We are going to add a little today, a little tomorrow, and at some point, we are going to say, 'Wow, this is starting to look pretty good.'"

For more information on the process of brain mapping, take a look at the next page.