Medical Student Research Fellowship for Summer 2011

Mentor:  Hanzhang Lu, Ph.D.                      
Department:   Advanced Imaging Research Center        
Room number: NE3.206
Mail Code:  8542                 
Phone number:  214-645-2761      
E-mail:  Hanzhang.Lu@utsouthwestern.edu                     
Project title:                Characterization of White Matter Hemodynamics with MRI

Human subjects IRB approved project number (where applicable):       STU 082010-238

Animal subjects IRB approved project number (where applicable):      

Project Type (patient-based research, animal-based research, or basic research; this characterization is only to permit a general classification for grouping similar types of projects)

Brief Description of Project:

White matter provides anatomic connections between spatially distinct cortical regions and allows efficient propagation of neural signals. Recent neuroimaging studies have provided evidences that temporal coherence of activities in different gray matter regions is dependent upon the microstructural organization of the white matter connecting them. White matter structural changes have also been implicated in neurological diseases that were previously thought to be primarily affecting cortical regions such as Alzheimer’s Disease. Despite mounting evidence of the role of white matter in understanding brain function, relatively little is known about the physiology of the white matter. The present study aims to investigate blood supply to the white matter in the human brain and its relationship with gray matter activity.

Neuroanatomy studies have revealed that blood vessels that perfuse white matter are branches of intracortical arteries that penetrate the cortical ribbon and often travel in parallel with the axon’s path. Previous neuroimaging studies have also demonstrated the presence of blood flow in the white matter, but have not studied its spatial distribution due to limited sensitivity, resolution and the lack of supporting techniques. White matter contains highly specialized fiber tracts. These fibers serve different functional purposes with some requiring long-distance and rapid signal propagation (e.g. corticospinal tract) and others requiring dense but shorter connections (e.g. tracts connecting association cortices). We therefore hypothesized that cerebral blood flow (CBF) in the white matter varies between fiber tracts and that the tract-specific CBF is correlated with the fiber’s structural property. Furthermore, given previous findings that functional connectivity in the gray matter is supported by white matter structural connection, we hypothesized that functional measures of the white matter, e.g. CBF, may have a strong relationship to gray matter connectivity.

In the present study, we will perform MRI experiments to measure CBF in the white matter and its change with inhalation of 5% CO2. CO2 is a potent vasodilator and has been shown to increase CBF in the gray matter. We hypothesize that white matter hemodynamics are different from that of gray matter in that CO2 inhalation would result in no change or even a decrease in CBF due to “stealing” effect from the gray matter. Healthy subjects with different age will be studied.

Previous Research Activities or Publications with Medical Students:

None