Interhemispheric interactions during sentence comprehension in patients with aphasia

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Neurolinguistics

Background:

• Left-hemisphere damage, common in stroke, often leads to aphasia, impacting language.
• The role of the right hemisphere (RH) in language recovery is debated, with theories suggesting compensation or maladaptive inhibition.
• Understanding inter-hemispheric connectivity is crucial for explaining language deficits and recovery patterns.

Purpose of the Study:

• To investigate inter-hemispheric effective connectivity during language processing in patients with post-stroke aphasia.
• To compare connectivity patterns between patients and healthy controls (age-matched and younger).
• To correlate connectivity measures with language comprehension performance in patients.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to assess effective connectivity.
• Dynamic Causal Modeling (DCM) was applied to analyze connectivity in specific brain regions (inferior frontal gyri and auditory cortices).
• Fifteen patients with post-stroke aphasia and control groups participated in a sentence comprehension task.

Main Results:

• Satisfactory DCM model fit was achieved in 9 out of 15 patients.
• In young controls, excitatory RA1-LA1 connectivity and inhibitory LIFG-to-A1 connections were observed.
• Patient connectivity, particularly top-down coupling (LIFG-to-A1), negatively correlated with sentence comprehension scores, suggesting maladaptive changes.

Conclusions:

• The study did not find evidence for new compensatory right-to-left excitation or left-to-right suppression in controls.
• Altered excitatory and inhibitory connections (homotopic and heterotopic) following left-hemisphere damage appear maladaptive.
• Disruptions in inter-hemispheric coordination and communication likely contribute to language deficits in aphasia.