Age-related top-down suppression deficit in the early stages of cortical visual memory processing

Abstract

In this study, electroencephalography (EEG) was used to examine the relationship between two leading hypotheses of cognitive aging, the inhibitory deficit and the processing speed hypothesis. We show that older adults exhibit a selective deficit in suppressing task-irrelevant information during visual working memory encoding, but only in the early stages of visual processing. Thus, the employment of suppressive mechanisms are not abolished with aging but rather delayed in time, revealing a decline in processing speed that is selective for the inhibition of irrelevant information. EEG spectral analysis of signals from frontal regions suggests that this results from excessive attention to distracting information early in the time course of viewing irrelevant stimuli. Subdividing the older population based on working memory performance revealed that impaired suppression of distracting information early in the visual processing stream is associated with poorer memory of task-relevant information. Thus, these data reconcile two cognitive aging hypotheses by revealing that an interaction of deficits in inhibition and processing speed contributes to agerelated cognitive impairment.aging ͉ working memory ͉ inhibitory deficit ͉ distraction ͉ attention C ognitive impairment associated with normal aging impacts multiple domains [e.g., attention, working memory (WM) and episodic memory (1)], prompting a search for underlying neural mechanisms that might account for such widespread deficits. Two of the leading cognitive aging hypotheses are the ''processing speed hypothesis,'' in which performance deficits are attributed to a decline in processing speed (2), and the ''inhibitory deficit hypothesis,'' which proposes that impairment in diverse cognitive abilities are the result of an inability to reduce interference from task-irrelevant information (3). Despite widespread behavioral evidence, physiological data characterizing the neural underpinnings of these age-related deficits, and notably the interactions between them, are limited.A recent functional magnetic resonance imaging (fMRI) study supports the presence of an age-related top-down modulation deficit in inhibitory control (4). Top-down modulation is the neural process that underlies our ability to focus on relevant information and ignore irrelevant distractions via both the enhancement and suppression of sensory cortical activity (5, 6). The fMRI data revealed that, although older adults were able to enhance visual cortical activity for relevant information to the same extent as younger individuals, they were unable to adequately suppress activity associated with irrelevant information, and this suppression deficit correlated with their impaired WM performance (4).The current study is directed at exploring the relationship between the inhibitory deficit and processing speed hypothesis, a goal that necessitates obtaining high temporal resolution neural data to dissect the time-course of age-related processing changes. Because of the vascular nature of the fMRI blood o...

Deficit in switching between functional brain networks underlies the impact of multitasking on working memory in older adults

“…From this perspective, our neural findings of persistent connectivity for the interruptor may reflect inadequate deletion of information that is no longer relevant. Therefore, this disengagement deficit seems to represent yet another example of failed inhibition in older adults, which has been extensively characterized as a deficit in suppressing distracting information (5,13,15). Thus, this finding serves as a conceptual bridge to unite age-related distraction and interruption effects under a common mechanism.…”

“…Functional MRI measures revealed that older individuals inappropriately direct excessive attention toward processing visual stimuli that are entirely irrelevant (i.e., distractions), and that this correlates with diminished WM performance (13). EEG studies further showed that this occurs early during visual processing (<200 ms after stimulus onset), whether or not individuals are prepared for the distractor (5,(13)(14)(15). Moreover, the degree that both distractors and interruptors are processed correlates with reduced WM performance in both younger and older adults (4,5).…”

Event-Related Brain Potentials in the Study of Inhibition: Cognitive Control, Source Localization and Age-Related Modulations

“…Within the first 200 ms, the young adults exhibited the largest P1 amplitude and earliest N1 latency for the attended faces, followed by passive faces and then ignored faces, whereas the older adults only exhibited the largest P1 amplitude and earliest N1 latency for the attended faces compared with passive faces. Gazzaley et al (2008) interpreted these results as an indication of sensory suppression deficits in older adults (because there were no differences between the passive and ignore conditions), as well as an indication of preserved enhancement processes (the same change in young and older adults between the passive and attend conditions). In an additional experiment with the selective attention delayed-recognition task, Anguera and Gazzaley (2012) …”

Frontal midline theta connectivity is related to efficiency of WM maintenance and is affected by aging

“…While the behavioral aspects of age-related decline in WM are well known , the changes of functional interactions between brain areas related to WM (especially during the maintenance period) across the lifespan are still largely unclear, and have not as yet been investigated by EEG studies. It is still a matter of debate which WM processes (encoding: Gazzaley et al, 2008;Karrasch et al, 2004, or maintenance: Cappell, Gmeindl, & Reuter-Lorenz, 2010) underlie much of the WM deficits observed in the elderly.…”