The Relationship Between Task-Related Aperiodic EEG Activity, Neural Inefficiency and Verbal Working Memory in Younger and Older Adults.

Younger adults consistently demonstrated steeper aperiodic slopes than older adults across task conditions.

• EEG was recorded from 24 younger adults (18-35 years) and 30 older adults (50-86 years)
• Age-related differences in the aperiodic exponent were observed during a modified Sternberg verbal working memory task
• The steeper slopes in younger adults are consistent with the neural noise hypothesis of cognitive aging
• This age difference was consistent across fixation and task conditions

Both age groups showed decreased (flattened) aperiodic exponents during retention relative to fixation, with minimal load-dependent effects.

• The flattening of the aperiodic exponent during retention was unexpected relative to prior hypotheses
• Load conditions included 1-letter, 3-letter, and 5-letter memory set sizes in a modified Sternberg task
• Minimal differences in the aperiodic exponent were observed across the three load conditions
• This pattern of task-related flattening occurred in both younger and older adult groups

The relationship between task-related aperiodic exponent changes and working memory performance was complex and dependent on the exponent at fixation, particularly in older adults.

• The fixation-period aperiodic exponent moderated the relationship between task-related exponent changes and WM performance
• This moderating effect was especially pronounced in older adults
• The complexity of the relationship suggests that a single measure of the aperiodic exponent is insufficient to characterize its role in WM performance
• Both baseline (fixation) and task-related (retention) exponent values contributed to explaining WM outcomes

Flatter aperiodic exponents during fixation and late retention were associated with greater neural inefficiency, reflected by increased P3b amplitudes without corresponding working memory performance improvements.

• Neural inefficiency was operationalized as larger P3b amplitudes that did not correspond to improved WM performance
• Flatter exponents at both fixation and late retention predicted greater neural inefficiency
• The P3b is an event-related potential component associated with stimulus processing and cognitive resource allocation
• This dissociation between neural activity and behavioral performance indicates less efficient neural processing in individuals with flatter exponents

The study was a reanalysis of previously published data examining EEG aperiodic activity in the context of verbal working memory and aging.

• The sample comprised 24 younger adults (18-35 years) and 30 older adults (50-86 years)
• A modified Sternberg task was used with three load conditions: 1-letter, 3-letter, and 5-letter sets
• EEG was recorded during the task to extract both aperiodic exponent measures and event-related potentials (P3b)
• The aperiodic exponent was analyzed during fixation and retention periods to capture both baseline and task-related neural dynamics