each individuals images resembled older brains, the poorer the performance on the tests of cognition.Brickman and his colleagues will next attempt to determine what factors might mediate the relationship between age and these structural and functional changes in the brainstudies that may help scientists develop treatments to halt or perhaps even reverse the effects of age on the brain.Most research into the aging brain has focused on gray matter, the darker-colored tissue of the brain composed mainly of the bodies of nerve cells (neurons). Gray matter includes such structures as the cerebral cortex, the thalamus, and the basal ganglia, and is believed to be the thinking center of the brain where memory, among other cognitive functions, is processed. As we age, some neurons shrink and others die, resulting in a loss of gray matter.Although less studied, white matterthe fibers (axons) that connect neurons within and between brain regionsalso shrinks with age. Axons transmit messages among neurons, and are encased in a sheath of fat called myelin. With aging, the thickness of the myelin decreases, resulting in reduced white matter densitya change that can be seen under a microscope, particularly around the brains ventricles (cavities containing cerebrospinal fluid) and in deep white matter. If this shrinkage or deterioration in the brains telephone wires is significant, it may cause interference in communication between areas of gray matter. In turn, this disrupted communication could impact a persons ability to perform complex, coordinated daily tasks, such as remembering to pay the bills on time or doing complicated mathematical calculations in ones head.At the Massachusetts Institute of Technology, David A. Ziegler and his colleagues used a fairly new MRI-based brain imaging technique, diffusion tensor imaging (DTI), to study white matter changes in healthy aging brains and how these changes are linked to cognitive performance. DTI measures the ease with which water molecules move in a particular direction through different types of tissue. Because bundles of myelinated axons create barriers that restrict the movement of water non-randomly, DTI can be used as an indirect measure of the integrity of white matterand, thus, of whether regions of white matter are particularly susceptible to the adverse effects of aging.The cognitive tasks chosen for the study were designed to assess episodic memory (the ability to remember specific events and their contexts), semantic memory (the ability to remember facts), and frontal lobe cognitive control processes (the ability to coordinate ones thoughts and actions). We found that white matter integrity was particularly reduced in the frontal-most parts of the brainareas such as the prefrontal cortex and the anterior portion of the corpus callosum, says Ziegler. We were also able to demonstrate that this decline in integrity is associated with a decreased ability to perform tasks that require cognitive controlprecisely those functions traditionally assigned to the frontal lobes. In contrast, performance on semantic and episodic memory tasks appears to relate more to integrity of white matter in other parts of the brain, such as regions underlying the parietal and temporal lobes.Next, Ziegler and his colleagues intend to determine the extent to which age-related functional