The cerebellum's role in WM during recovery from TBI

Open Access
Author:
Medaglia, John Dominic
Graduate Program:
Psychology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 05, 2014
Committee Members:
  • Frank Gerard Hillary, Dissertation Advisor
  • Peter Andrew Arnett, Committee Member
  • Rick Owen Gilmore, Committee Member
  • Peter Cm Molenaar, Committee Member
Keywords:
  • working memory
  • TBI
  • fMRI
  • cerebellum
  • graph theory
Abstract:
Previous studies of WM processing during recovery from traumatic brain injury (TBI) have primarily focused on the nature of functional recruitment of the right dorsolateral prefrontal, anterior cingulate, and inferior parietal cortices following injury. However, overwhelming evidence suggests a role for the cerebellum in a wide range of cognitive processes, including WM. The cerebellum may contribute important timing, patterning, and associative learning functions to WM in healthy individuals and be especially recruited following diffuse injury. Two studies were conducted to examine the contribution of the cerebellum to speeded working memory (WM) processing during recovery from TBI. Analysis 1 was a general linear modeling examination of the relationship between the BOLD fMRI signal in the cerebellum and WM performance. Analysis 2 was a graph theoretical analysis of the nature of whole brain and cerebellar connectivity. For each study, the influence of group, task load, and practice on BOLD activity was examined. Activity in all cerebellar lobules was greater in TBI than controls despite lower functional connectivity with neocortical regions. Response times during the cognitive task significantly predicted BOLD signal in all WM cerebellar lobules (i.e., VI, Crus I, Crus II, VIIB, VIIIA). While no main effects of TBI were found on overall network connectivity during the WM task, most WM lobules demonstrated increased clustering with the rest of the network despite weaker functional connections. Only modest effects of practice and load were found. Thus, local cerebellar resources representing timing, pattern formation, and associative learning functions are recruited following injury similarly to those in the neocortical WM system. In conditions of speeded WM processing, variations load and exposure to task over time do not yield pronounced effects. It is likely that cerebellar resources are recruited at a spatiotemporal scale corresponding to momentary task demands to support low load WM efficiency.