The Neuroimaging Revolution
January 11, 2008
One of the most exciting scientific advances of the past fifty years has been the development of complex neuroimaging techniques. Since computerized axial tomography (CAT or CT) was introduced in the 1970s we have seen the development of positron emission tomography (PET), magnetic resonance imaging (MRI), and functional MRIs (fMRI), each more effective than the one before, and each allowing for a drastically improved understanding of the brain and behavior. The dominant method of imaging through the past twenty years of brain research has been the fMRI. MRIs create an image of the brain out of radio waves emitted by hydrogen atoms in the body when they are manipulated by a magnetic field. fMRIs go a step further, allowing for a measurement of actual brain activity. When brain areas are active, they have an increased need for oxygen, and thus there is an increased amount of oxygenated blood moved to that area. fMRIs take advantage of the fact that oxygenated and deoxygenated blood have different magnetic resonance signals, and create an image of brain activity based on blood oxygenation levels. Here are pictures of an MRI (left) and fMRI (right):
fMRIs are effective and now integral in brain science, but don't think for a second that the desire to create precise brain imaging techniques ends there. There are a number of other techniques still being perfected that you may not hear about until they become more prevalent. One that is already starting to now give us a more complete picture of the brain is diffusion tensor imaging (DTI). While MRI shows the major structures of the brain, it has not been able to recreate the connections between those structures, such as the white matter tracts that connect the two hemispheres of our brain. DTI uses measurement of water diffusion along nerve fibers to image this subarchitecture. Compare the colorful DTI picture below to the MRI and fMRI pictures above.
DTI has already begun to be utilized in research. Randy Buckner and colleagues used DTI to measure white matter integrity in older patients. They studied it along with fMRI, and found that, in older individuals who had experienced a loss of cognitive ability, the integrity of white matter connections was decreased along with that of functional connections. It is hoped that the use of DTI will provide insight into the cognitive loss associated with aging, as well as into dementias like Alzheimer's disease.