TBI : DMN Flashcards
What have fMRI studies shown us about TBI? (and who?)
Studies using fMRI have demonstrated changes in interactions between nodes in the default mode network (DMN) (Bonnelle et al., 2011).
What does the DMN consist of?
Brain regions that have high metabolic activity and highly coordinated activity.
What are the core nodes of the DMN?
Posterior cingulate cortex (PCC), ventromedial prefrontal cortex (VMPFC) and parahippocampal gyrus
Besides TBI, when is there damage to the DMN (and who?)
Damage to the connectivity and function of these nodes is observed in many types of neurological and psychiatric disease (Leech et al., 2014).
What type of DMN network damage is seen in TBI? (and who?)
In TBI, varying amounts of damage are seen within the cingulum bundle (Bonnelle et al., 2011)—a tract that includes connections between the PCC and VMPFC as well as parahippocampal gyrus and PCC
What are the implications of damage to the cingulum bundle?
Damage correlates with reductions in functional connectivity within the DMN and impairments of sustained attention, whereby patients are unable to maintain attentional focus over time.
What normally happens to the DMN during tasks? (and who?)
The DMN usually shows load-dependent deactivation as task difficulty increases (Singh et al., 2008)
What happens if DMN doesn’t deactivate?
Failure of this network to deactivate has been associated with poorer cognitive function in both healthy individuals and patients with TBI
What studies have implicated dysfunctional FC in TBI patients?
De Simoni et al., (2016)
Using resting-state fMRI to compare 19 individuals with post-traumatic amnesia (PTA) after TBI (an indication of severe TBI) and TBI with controls
What did De Simoni find?
Found that the TBI patients, in particular those with PTA, demonstrated abnormal functional connectivity between the parahippocampal gyrus and PCC; the strength of which correlated with associative memory performance and speed of information processing.
What did diffusion MRI of PTA patients show>
Evidence of widespread traumatic axonal injury which was greatest at the cingulum bundle.
What did De Simoni’s study suggest?
Memory impairment acutely after TBI results from altered parahippocampal functional connectivity, perhaps secondary to the effects of axonal injury on white matter tracts connecting limbic structures involved in memory processing.
