Owen Carmichael, Ph.D.
Associate Professor and Director of Biomedical Imaging
Associate Professor and Director of Biomedical Imaging
The brain is active when one is just sitting there staring off into space, not performing any noteworthy mental task. Neurons are firing in a very coordinated fashion even though they are not being provoked to do so. In particular, there is a network of brain regions, termed the “default mode network,” whose neurons fire in a concerted fashion in individuals who are at rest. A depiction of some of the brain regions that are in the default mode network, provided by postdoctoral fellow Jing He based on functional MRI data, is shown at upper left. It is not entirely clear why this network-level brain activity is going on despite a lack of overt mental tasks. It is also unclear why the degree of coordination of this activity—called “functional connectivity”—is diminished in elderly individuals, individuals who harbor Alzheimer’s disease pathology in the brain, individuals with genetic risk factors for Alzheimer’s disease, and those who show signs of the disease clinically. I have been working on functional MRI data collected in elderly individuals who are at rest in an attempt to address these questions.
One possibility is that the functional connectivity is there to compensate for brain damage of the type that is caused by the wear and tear of life or by Alzheimer’s disease. If the brain is injured, perhaps the coordinated activity fires up, like turning up the idle on an old car. Jing’s data supports this notion: among individuals with the smallest amount of gray matter (i.e., the most injured brains), the functional connectivity was greatest. And, both gray matter volume and functional connectivity were associated with cognitive functioning. While there are numerous other roles that functional connectivity could be playing, this intriguing finding suggests that functional connectivity may be a marker of brain compensation.
Publications:
Jing He, Owen Carmichael, Evan Fletcher, Baljeet Singh, Ana-Maria Iosif, Oliver Martinez, Bruce Reed, Andy Yonelinas, Charles DeCarli. Influence of Functional Connectivity and Structural MRI Measures on Episodic Memory. Neurobiology of Aging, Volume 33, Issue 11, November 2012, Pages 2612-2620. DOI