Picturing the mind at work pg. 2
The explosion of fMRI studies in psychiatry and psychology has revealed volumes of information about individual brain regions and their principal functions.
While this may convey the rather simplistic notion that the brain is highly compartmentalized, another imaging technique based on MRI, diffusion tensor imaging (DTI), may help weave these isolated islands of brain activity back together again into a functional network.
“With fMRI, you can look at brain function—where in the brain certain information is processed,” says Adam W. Anderson, Ph.D., associate professor of Biomedical Engineering and of Radiology at Vanderbilt. “With DTI, you can look at the connection between areas of the brain that are processing that information.”
From the energy emitted by the nuclei of hydrogen atoms in the presence of a magnetic field, MRI can generate exquisitely detailed images of soft tissues, including the grayish parts of the brain that contain the neurons (called “gray matter”).
DTI, on the other hand, illuminates “white matter,” bundles of long fibers (axons) that transmit signals between different parts of the brain. In particular, the technique measures “anisotropy,” the degree to which water movement is greater along fibers than in other directions.
Anisotropy may help explain why some patients with schizophrenia experience auditory hallucinations. In 2005, Swiss researchers reported finding increased anisotropy in the brains of patients who frequently heard voices, particularly in the white-matter tracts that connected hearing and language centers.
Increased anisotropy is a measure of greater connectivity in the axon bundles. Neurons that are too strongly coupled to each other may fire off signals too readily, resulting in over-activation of parts of the brain that process external sounds and language, the researchers reported.
For patients with schizophrenia, this may explain the inability to distinguish their own, self-generated thoughts from external speech.
The Swiss report, entitled “Pathways That Make Voices,” reinforces the value of DTI in exploring other neurological and psychiatric diseases, says Anderson.
In collaboration with other Vanderbilt researchers, Anderson is using the technique to investigate known white-matter diseases such as multiple sclerosis, and to determine the effects of prenatal cocaine exposure on brain connectivity.
DTI and other MRI techniques also are proving useful to understanding how the developing brain is wired, and how conditions such as premature birth can affect cognitive development. The goal is to find ways to prevent “anatomic disturbances” from impairing “functional capacities,” according to Anderson, Gore and their colleagues at Yale.
“Neuropsychologists have spent a lot of time looking at the brain as it falls apart from injury,” adds imaging pioneer Marcus E. Raichle, M.D., professor of Radiology, Neurology and Anatomy & Neurobiology at Washington University School of Medicine in St. Louis. “But it would be equally important to watch it being put together during development.”