How right hemisphere damage after stroke can impair speech comprehension

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neurolinguistics

Background:

• Acquired language disorders are typically linked to left hemisphere brain damage.
• Right hemisphere strokes are often presumed to cause language difficulties only in cases of atypical brain organization.

Purpose of the Study:

• To investigate the mechanisms and prevalence of language disorders following right hemisphere strokes.
• To identify specific brain regions and functions affected by right hemisphere damage that lead to language deficits.

Main Methods:

• Behavioral and lesion data from stroke patients (n=475) were analyzed.
• Functional MRI (fMRI) was used in neurologically normal individuals to map brain activity.
• Patients with right hemisphere strokes and auditory sentence-to-picture matching impairments were compared to those without such impairments.

Main Results:

• Right hemisphere strokes frequently impaired auditory sentence-to-picture matching, unlike left hemisphere strokes which primarily affected spoken picture description.
• Patients with comprehension deficits showed significant damage to the right superior longitudinal fasciculus and right inferior frontal sulcus.
• Damage to these right hemisphere regions resulted in long-term speech comprehension difficulties in 67% of affected patients.
• fMRI revealed that the right inferior frontal sulcus is involved in tasks requiring high working memory capacity for language processing.

Conclusions:

• The right inferior frontal cortex plays a crucial role in executive functions, specifically working memory, which is vital for sentence comprehension.
• Right hemisphere strokes can cause substantial and long-lasting language deficits, independent of atypical language lateralization.
• These findings challenge the traditional view of language lateralization and highlight the contribution of the right hemisphere to language processing and executive functions.