How Brain Mapping Works

In mapping brain functions, scientists use imaging to watch the brain working on various tasks. Charles Wilson, a neurobiologist at the University of Texas at San Antonio, explains localization of function this way:

Brain mapping also looks from the outside in. It examines how our environment changes our brain's structure by studying, for instance, how the brain changes physically through the learning and aging processes. Brain mapping also examines what goes wrong physically in the brain during mental illnesses and other brain diseases.

Finally, brain mapping aims to give us a thorough picture of our brain's structure.

Google Earth shows us satellite images of our planet and zooms in to continents, countries, states, cities, highways, streets and buildings. A complete structural map of our brain might be similar.

It could show us our whole brain; all the regions, functional lobes, specialized centers, thick neuron "bundles" connecting brain parts, neuron circuits, single neurons, junctions between neurons and finally, neuron parts. Scientists are still developing the parts that might form this massive map.

Brain mapping uses a collection of many different tools. Researchers must collect images of the brain, turn those images into data, and then use that data to analyze what happens in the brain as it develops.

Scientists use both functional and structural neuroimaging in brain mapping research. They take pictures of healthy brains and compare them to diseased brains.

In addition, they examine brains taken from humans, primates and 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 brain mapping 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 called connectomics. The "wiring diagram" of a brain is called a connectome [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 as Brainbow, 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 the ATLUM, or automatic 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 an electron 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? Explore what we can learn from mapping the human brain in the next section.

Can a phMRI Study Pain?

Since 1997, a group of researchers at Britain's Oxford Centre for Functional Magnetic Resonance Imaging of the Brain have recorded images of patients' brains as they experience pain and various forms of relief including distraction and medication.

By measuring a drug's effect on the brain, scientists have been able to learn more about analgesic and psychiatric drugs.

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:

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 like autism may have a structural basis in the brain. Lichtman points out that autism is thought to involve a series of unique 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 differs from a mouse without autism.

Scientists have also sought to illustrate the effects of various psychiatric disorders in the brain, with some success. Brain imaging on these patients revealed structural abnormalities. For example, structural MRI has shown that schizophrenic patients lose matter in the temporal and prefrontal cortex over time [Source: Thompson et al.].

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?

Doctors and scientists have learned more from brain mapping than this article can cover. Here are two highlights:

Sarcasm

We detect sarcasm using a brain region called the right parahippocampal gyrus. Researchers discovered this using functional MRI on patients with deterioration in that region and have lost all sense of sarcasm [source: Hurley].

Consciousness

According to Rodolfo Llinas of New York University, we can divide the brain into a synchronization center deep in the brain and neuron loops that give us higher thought.

We feel conscious when the center keeps the loops working in harmony. But if either part is damaged, we may lose some or all consciousness, says Nicholas Schiff at Cornell University's Weill Medical College.

This may explain why patients with no outward signs of consciousness for years may show completely normal brain activity in response to a familiar voice. They have loops working in isolation, like the neural networks that process language [source: Zimmer].

Neuroinformatics places all the data we have on the brain on the internet in usable form. The data include images, models of neuron behavior and maps of the genes that 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 people with a certain brain architecture predisposed to bipolar disorder? This question, and many others, may one day be answered by computer programs that reanalyze 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:

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.

This complete, Google Earth–type of map is stalled 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.

Mapping the Fruit Fly Brain

For many years, scientists were only able to produce complete maps of interconnecting neurons for species with very simple "brains" consisting of only several hundred neurons. The first of these was Caenorhabditis elegans, "a worm that's a millimeter long and has 300 nerve cells," says Lichtman.

In March 2023, researchers released the first connectome of a complex brain, that of a larval fruit fly (Drosophila melanogaster). Fruit fly brains may seem simple until you realize they have 3,000 neurons and half a million synapses. Mapping the fruit fly brain took over five years.

A Complete Map of the Human Brain

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 may be 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 from birth to death. "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:

You Use It All

It is a myth that we use only 10 percent of our brains. We use it all. Brain images have collectively documented activity in all parts. What's more, damage to a small area can wipe out major abilities. Read more about the 10 percent brain myth on professor Eric Chudler's website at the University of Washington.