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,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 techniques take images of the brain:
- Computer axial tomography (CAT) scan X-rays the brain from many angles and show structural abnormalities.
- Structural magnetic resonance imaging takes advantage of water in the brain to create images with better resolution than a CAT scan.
- Diffusion tensor-MRI (DTI) images “tracts” of neurons that connect brain regions by following water movement in the brain.
These techniques examine brain activity:
- Electroencephalography (EEG) indicates electrically active locations in the brain using detectors implanted in the brain or worn on a cap.
- Positron Emission Technology(PET) takes images of radioactive markers in the brain.
- Functional MRI (fMRI) shows images of brain activity while subjects work on various tasks.
- Pharmacological functional MRI (phMRI) shows brain activity as drugs are administered.
- Transcranial magnetic stimulation (TMS)noninvasively stimulates parts of the brain to trigger certain behaviors.
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 . “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? Learn what we can learn from mapping the human brain.
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.
Developmental disorders like autism may 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 that schizophrenic patients lose matter in the temporal and prefrontal cortex over time.
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.