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Brain Imaging and Bipolar Disorder

Rashmi Nemade, Ph.D. & Mark Dombeck, Ph.D.

Brain imaging technology has yielded significant insights into bipolar diseases. Brain imaging techniques allow visualization of the whole living brain or slices of the living brain without ever having to perform surgery. Because these procedures are non-invasive and give lots of information about brain structure and function, they have revolutionized research and medicine. Various studies have documented differences in brain structures and functions that are typically present when bipolar and non-bipolar (e.g., healthy) brains are compared.

Structural studies measure brain composition using technologies such as Computerized Axial Tomography (CAT) and Magnetic Resonance Imaging (MRI). In CAT, X-rays are used to scan the brain. With each scan, a digital photograph is taken and a computer compiles these photographs into a three-dimensional image of the brain. In MRI, the brain is scanned by a magnet which is linked to a computer. Each MRI scan produces hundreds of digital images from multiple angles to produce an accurate three-dimensional image. Using these methods, researchers have found enlarged ventricle spaces (spaces which carry cerebrospinal fluid through and around the brain) in those with a bipolar diagnosis. Larger ventricles indicate less brain tissue is present as a whole within the brain and suggests that either deterioration has occurred, or that bipolar brains develop differently than normal brain controls. Another structural anomaly observed is that bipolar brains tend to contain an abnormal amount of small, white areas in the brain known as 'white matter hyperintensities'. White matter is involved in transmitting information from one part of the brain to the other. Patients who have these hyperintensities have an occurrence of bipolar disorder that is three times as likely as the general population. Furthermore, in bipolar patients, there is a reduction in glial cells, which are cells that insulate brain neurons, making them communicate more efficiently. Less glial cell density within bipolar brains means that these brains do not communicate as efficiently as their normal counterparts. If the bipolar brain has a difficult time conversing with itself because of white matter hyperintensities and/or glial cell degeneration, mood fluctuations might be a natural result of this miscommunication. The imaging data are relatively new and preliminary, and their meaning is not known definitively at this time. As more data become available, a clearer picture of how brain structure affects bipolar diagnosis will emerge.

Functional brain imaging studies measure the brain's metabolic rates and neurological activity using Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and functional MRI (fMRI) technologies. In both PET and SPECT, a safe radioactive tracer chemical is injected into the blood stream. This tracer is chosen for its affinity for binding to specific and particular areas inside the brain that researchers wish to study. Most commonly a radioactively labeled sugar molecule is injected and allowed time to become concentrated in tissues of interest. The brain is then scanned for how quickly the sugar and oxygen are metabolized. The major difference between PET and SPECT is that PET produces a three-dimensional image of the brain while SPECT creates two-dimensional slices of the brain.

While PET and SPECT focus on metabolic rates to determine neurological activity levels, fMRI technology yields information by measuring blood flow within the brain. Magnets exploit the natural magnetic properties of blood (blood cells contain iron) allowing an image to be produced on a computer telling researchers which areas of the brain have the highest and lowest blood flows. These imaging technologies make it possible to create real-time movies documenting the functions of the various parts of the brain. Brain parts that consume more oxygen and sugar are working harder than other brain parts.

There is some evidence to suggest that brain parts work harder and possibly faster during periods of mania. Furthermore, using these techniques, researchers have found abnormalities in areas of the bipolar brain important for regulation of mood and logical connections between language and memory. Studies of this type are of the cutting edge variety and will (hopefully) shortly yield a precise understanding of which parts of the brain are most active during mania and depression, and how bipolar patients "think differently" (if, in fact, they do) compared to people without bipolar diagnoses.