Disconnection between the default mode network and medial temporal lobes in post-traumatic amnesia
Sara De Simoni1, Patrick J Grover1, Peter O Jenkins1
11 Computational, Cognitive and Clinical Neuroimaging Laboratory, Imperial College London, Division of Brain Sciences, Hammersmith Hospital, London, UK.
Brain : a Journal of Neurology
|November 1, 2016
Summary
Post-traumatic amnesia after brain injury is linked to disrupted connections within the brain's default mode network. This study shows impaired functional connectivity in patients with post-traumatic amnesia, improving as memory recovers.
Area of Science:
- Neuroscience
- Cognitive Neurology
- Radiology
Background:
- Post-traumatic amnesia (PTA) is a common state after traumatic brain injury (TBI), characterized by confusion and memory deficits.
- The underlying pathophysiology of PTA remains poorly understood, despite its significance as a predictor of functional outcomes.
- Memory relies on limbic structures and the default mode network (DMN), whose connectivity can be assessed using resting-state fMRI.
Purpose of the Study:
- To investigate the hypothesis that mnemonic symptoms in PTA result from functional disconnection within the DMN.
- To assess transient disconnection between the hippocampus/parahippocampus and cortical memory regions in TBI patients with PTA.
- To explore the relationship between altered functional connectivity, cognitive deficits, and axonal injury in PTA.
Main Methods:
- Resting-state functional magnetic resonance imaging (fMRI) was used to assess DMN connectivity in 19 TBI patients.
- Patients were categorized into PTA and TBI control groups based on paired associates learning task performance.
- Diffusion MRI measured widespread traumatic axonal injury, particularly within the cingulum bundle.
Main Results:
- Patients with PTA exhibited impaired associative memory, information processing speed, and spatial working memory.
- Abnormal functional connectivity was observed between the parahippocampal gyrus and posterior cingulate cortex in PTA patients.
- The strength of this connection correlated with memory and processing speed, normalizing with functional improvement.
Conclusions:
- Acute memory impairment following TBI is associated with altered parahippocampal functional connectivity.
- Axonal injury within the cingulum bundle may underlie these connectivity changes, affecting limbic structures crucial for memory.
- These findings offer novel insights into the pathophysiology of PTA and its mnemonic symptoms.
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