Aging modulates the oscillatory dynamics underlying successful working memory encoding and maintenance

Abstract

Working memory is central to the execution of many daily functions and is typically divided into three phases: encoding, maintenance, and retrieval. While working memory performance has been repeatedly shown to decline with age, less is known regarding the underlying neural processes. We examined age-related differences in the neural dynamics that serve working memory by recording high-density magnetoencephalography (MEG) in younger and older adults while they performed a modified, high-load Sternberg working memory task with letters as stimuli. MEG data were evaluated in the time-frequency domain and significant oscillatory responses were imaged using a beamformer. A hierarchical regression was performed to investigate whether age moderated the relationship between oscillatory activity and accuracy on the working memory task. Our results indicated that the spatiotemporal dynamics of oscillatory activity in language-related areas of the left fronto-temporal cortices were similar across groups. Age-related differences emerged during early encoding in the right-hemispheric homologue of Wernicke's area. Slightly later, group differences emerged in the homologue of Broca's area and these persisted throughout memory maintenance. Additionally, occipital alpha activity during maintenance was stronger, occurred earlier, and involved more cortical tissue in older adults. Finally, age significantly moderated the relationship between accuracy and neural activity in the prefrontal cortices. In younger adults, as prefrontal activity decreased, accuracy tended to increase. Our results are consistent with predictions of the compensation-related utilization of neural circuits hypothesis (CRUNCH). Such differences in the oscillatory dynamics could reflect compensatory mechanisms, which would aid working memory performance in older age.

Neuroimaging with magnetoencephalography: A dynamic view of brain pathophysiology

“…For example, Proskovec and colleagues reported widespread neural activity in left fronto-temporal regions of both young and older adults during the encoding and maintenance periods of a verbal working memory task, but only older adults also engaged the right prefrontal cortices during task performance. 156 Results for the retrieval phase of working memory were reported by Aine et al 157 Notably, no age-related differences in working memory performance were observed in either of these studies. 156-157 Together, these studies support the compensation hypothesis of cognitive aging.…”

“…156 Results for the retrieval phase of working memory were reported by Aine et al 157 Notably, no age-related differences in working memory performance were observed in either of these studies. 156-157 Together, these studies support the compensation hypothesis of cognitive aging. 136 Essentially, older adults recruited more neural resources during working memory performance across encoding, maintenance, and retrieval periods compared with younger adults, while performance was relatively equal between groups.…”

“…Interestingly, the Proskovec study also found strong alpha (9-12 Hz) synchronization in the occipital cortices during memory maintenance in both age groups, although this response occurred earlier and encompassed more cortical tissue in older adults (Figure 8). 156 Occipital alpha synchronization is believed to reflect inhibition of the dorsal visual stream during memory maintenance, which would aid in blocking incoming visual distractions and help preserve memory representations in more anterior cortical regions. 158-160 Thus, the earlier and more widespread increase in occipital alpha activity in older adults likely reflects an additional compensatory mechanism.…”

“…Conversely, older adults demonstrated a progressive increase in alpha activity across bilateral occipital cortices, with the increases in alpha occurring earlier and involving more cortical tissue in older adults relative to younger adults. 156 Such alpha synchronization is thought to decrease or inhibit visual input and thereby aid in maintaining memory representations.…”

Attention training improves aberrant neural dynamics during working memory processing in veterans with PTSD

“…The MEG preprocessing and imaging analysis pipeline was closely based on the methods reported in our recent WM papers (Heinrichs-Graham & Wilson, 2015; McDermott et al, 2015; Proskovec, Heinrichs-Graham, & Wilson, 2016; Wiesman et al, 2016). The continuous magnetic time series was divided into epochs of 6,900 ms duration, with 0 ms being the onset of the encoding grid and the baseline being the −400–0 ms time bin (see Fig.…”