Dissertation Defense: Charles Lynch
Candidate Name: Charles Lynch
Dissertation Adviser: Chandan J. Vaidya, Ph.D.
Title: Precision Mapping and Transcranial Magnetic Stimulation of Cortical Hubs in Individuals
Hub nodes serve important roles in modular physical, social, and biological systems. This dissertation focuses upon the role of hubs in one of the most complex, poorly understood biological systems in nature – the human brain. In theory, hub brain areas mapped using non-invasive neuroimaging techniques are compelling sites for intervention in a variety of psychiatric and neurologic conditions. Two challenges, however, currently preclude the development of hub-centric interventions. First, interventions necessarily require mapping targets precisely on an individual basis, but neuroimaging is routinely performed at the group-level. Second, there is no empirical evidence that hub brain areas are causally involved in cognition and behavior. This dissertation describes two investigations that address these challenges. Using a public dataset of highly-sampled individuals, the first investigation revealed that different areas of cortex function as hubs in different individuals, but that single-subject hub estimates were nonetheless highly-reproducible within an individual when using large quantities of per-individual resting-state fMRI data. The second investigation, using a prospective, within-subjects, double-blind design, tested the prediction that inhibiting individual-specific hubs with transcranial magnetic stimulation would disrupt information processing during working-memory, more so than inhibition of nearby non-hubs. Despite hubs and non-hubs stimulation sites being separated by only a few centimeters on the same gyrus in each subject, a drift diffusion model revealed that information processing was disrupted more by hub inhibition. A post-hoc analyses indicated that inhibition of a specific hub subtype linking select control networks.
Friday, May 25 at 1:00pm to 3:00pm
White-Gravenor Hall, 405
37th and O St., N.W., Washington