When right becomes less right: Neural dedifferentiation during suprasegmental speech processing in the aging brain.

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Cognitive Aging

Background:

• The 'Asymmetric Sampling in Time' (AST) hypothesis suggests rightward lateralization for speech perception in younger adults.
• Investigating how auditory processing and brain lateralization change with age is crucial for understanding cognitive aging.

Purpose of the Study:

• To examine if the AST hypothesis's pattern of functional lateralization for speech perception in younger adults is replicated in older adults.
• To explore the relationship between structural brain measurements and functional auditory responses in the aging population.

Main Methods:

• Utilized event-related sparse-temporal acquisition fMRI and structural MRI in older adults (n=26, mean age=70.64).
• Participants performed an auditory pattern-matching task with time-reversed sentences of varying temporal integrity.
• Analyzed functional lateralization in auditory regions of interest: Heschl's gyrus (HG), planum temporale (PT), and posterior lateral superior temporal gyrus (pSTG).

Main Results:

• Older adults did not exhibit the expected rightward lateralization in HG, PT, and pSTG for suprasegmental speech cues.
• Frequentist and Bayesian analyses indicated no significant functional lateralization for speech processing in older participants.
• A positive correlation was found between right PT thickness and reduced variance in lateralization, suggesting structural influences on functional consistency.

Conclusions:

• The findings challenge the universal application of the AST hypothesis across the lifespan, indicating altered speech processing lateralization in older age.
• Structural integrity of the right planum temporale may play a role in stabilizing auditory functional responses in aging.
• This research extends the understanding of auditory cortex division of labor during spoken language processing to a lifespan perspective.