Neurophysiological alterations during strategy-based verbal learning in traumatic brain injury

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neurology

Background:

• Verbal learning and strategic processing deficits are common after traumatic brain injury (TBI).
• The underlying neurophysiological mechanisms of these deficits are not well understood.

Purpose of the Study:

• To investigate the neurophysiological mechanisms of verbal learning and strategic processing deficits in individuals with chronic TBI.
• To examine brain activity and functional connectivity during verbal encoding tasks using functional magnetic resonance imaging (fMRI).

Main Methods:

• fMRI scans were conducted on 25 individuals with chronic TBI and 20 healthy controls during verbal encoding tasks.
• Participants encoded word lists under varying strategic processing loads: unrelated words, spontaneous related words, and directed related words.
• Behavioral measures included free recall, recognition, and semantic clustering; fMRI assessed brain activity and functional connectivity.

Main Results:

• Behavioral performance improved with increased strategic load (Unrelated < Spontaneous < Directed) in both groups, with TBI individuals showing parallel but impaired performance.
• fMRI revealed decreased activity in the left dorsolateral prefrontal cortex (DLPFC; BA 9) and left angular/supramarginal gyri (BA 39/40) in TBI participants.
• Functional connectivity analysis showed a breakdown between the DLPFC and other regions in TBI participants specifically under directed strategic processing conditions.

Conclusions:

• The DLPFC becomes functionally decoupled from other brain regions during strategic processing in individuals with TBI.
• This decoupling specifically impacts tasks requiring strategic control, contributing to verbal learning deficits after TBI.
• Targeting strategies to re-couple the DLPFC may offer a promising avenue for TBI cognitive rehabilitation.