Cortical speech envelope tracking reflects lesion-symptom profiles in post-stroke aphasia

Area of Science:

• Neuroscience
• Speech and Hearing Science
• Neurology

Background:

• Comprehending connected speech is vital for interaction but impaired in post-stroke aphasia.
• Understanding neural mechanisms of speech listening is crucial for effective assessment and treatment.
• Neural speech tracking offers insights into naturalistic speech processing and its causal role in comprehension.

Purpose of the Study:

• To investigate neural speech tracking in individuals with aphasia due to left temporal or frontal lesions.
• To examine the relationship between neural tracking (theta and delta rates) and speech comprehension abilities.
• To explore how lesion location and severity influence neural tracking and comprehension.

Main Methods:

• Electroencephalography (EEG) recorded during story listening in individuals with aphasia (temporal/frontal groups) and controls.
• Participants listened to clear, unintelligible, and controlled low-intelligibility stories.
• Analyses included envelope tracking (theta/delta rates), neural decoding, and encoding, with linear mixed-effects regression for group comparisons.

Main Results:

• The temporal group showed significantly impaired comprehension compared to frontal and control groups.
• Speech intelligibility affected delta tracking (higher-order processing), but not theta tracking (sensory responses).
• Reduced theta and delta tracking observed in the temporal group; theta tracking showed a lesion-specific, quadratic relationship with comprehension.

Conclusions:

• Neural speech tracking, particularly theta tracking, reflects both lesion location and symptom severity in aphasia.
• Reduced theta tracking in temporal lobe lesions may hinder speech comprehension by impairing auditory stream representation.
• Envelope tracking is a promising method for investigating speech comprehension mechanisms in neurological conditions like aphasia.