Bilateral recruitment of prefrontal cortex in working memory is a general strategy to master cognitive challenges

Previous neuroimaging research has consistently shown that older adults often exhibit bilateral brain activation during cognitive tasks where younger adults show unilateral activation, a phenomenon known as Hemispheric Asymmetry Reduction in Older Adults (HAROLD). While this has traditionally been interpreted as an age-specific compensation mechanism for neurocognitive decline, the authors investigated whether this bilateral recruitment is actually a general coping strategy triggered by high task difficulty, regardless of age.

To test this, the researchers used functional magnetic resonance imaging (fMRI) to compare brain activity in young and older adults. They employed a delayed match-to-sample working memory (WM) task across three domains: verbal, spatial, and object-based. Crucially, they matched subjective task difficulty for each individual by calibrating memory load to their specific WM capacity. They specifically examined the dorsolateral prefrontal cortex (DLPFC), anterior prefrontal cortex (aPFC), and ventrolateral prefrontal cortex (VLPFC) to see if activation patterns shifted from unilateral to bilateral as tasks became more demanding.

The study found that bilateral recruitment of the DLPFC and aPFC is not an age-specific phenomenon. Instead, both young and older adults shifted from unilateral to bilateral activation in these prefrontal regions when working memory tasks reached their subjective capacity limits. This shift occurred across all tested domains, suggesting a domain-general support mechanism. Conversely, language-related areas, such as the VLPFC, maintained a unilateral activation pattern even during highly demanding tasks, indicating that this compensatory bilaterality is largely confined to the more flexible prefrontal cortex.

This research challenges the view that bilateral brain activation in aging is merely a sign of compensatory decline. By demonstrating that younger adults utilize the same bilateral strategy under high cognitive load, the study supports the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH). It highlights that the prefrontal cortex acts as a flexible resource that can recruit contralateral counterparts to maintain performance when task demands exceed the capacity of a single hemisphere.