Summary: A new USC-led study links age-related increases in distractibility to changes in the locus coeruleus, a small brainstem region that helps sharpen attention under stress or emotional arousal. The findings help explain why older adults can struggle to focus when aroused or stressed.
Source: USC
Older adults become more prone to distraction when emotionally aroused or stressed, and researchers say a weakening of the locus coeruleus — a tiny but widely connected brainstem region — may underlie this change in attention with age.
Researchers led by Mara Mather at the USC Leonard Davis School of Gerontology examined how the locus coeruleus and its network connections influence attention in younger and older adults. The locus coeruleus releases norepinephrine, a neurotransmitter that adjusts the brain’s signal-to-noise ratio: it amplifies highly active neural signals while suppressing weaker ones, helping us focus on what matters most during moments of stress or excitement.
The study found that while arousal narrowed attention in younger adults—amplifying relevant information and suppressing distractions—older adults showed a different pattern. Under arousal, older participants exhibited increased processing of both salient and non-salient stimuli, making them more likely to be distracted by irrelevant information.
“When younger adults try hard, the arousal that accompanies effort tends to boost their ability to ignore distractions,” said Mather, director of the USC Emotion and Cognition Laboratory and a professor at USC Dornsife. “But in older adults, that same arousal appears to make both target information and irrelevant input stand out, reducing selectivity.”
For example, an older person taking a memory test in a clinic may concentrate intensely, but background noises or unrelated thoughts may capture their attention more readily than they would in a younger person.
The study was published May 7 in Nature Human Behavior.
The locus coeruleus and Alzheimer’s-related pathology
Previous work from Mather’s lab has highlighted the locus coeruleus not only as a key regulator of attention and memory but also as an early site for tau pathology — the protein tangles associated with Alzheimer’s disease. Tau accumulation in the locus coeruleus can begin decades before clinical symptoms, making its functional changes across the lifespan an important area of study for aging and dementia research.
Mather and colleagues emphasize that understanding how locus coeruleus function and connectivity change with age could inform strategies to protect cognitive function and delay or mitigate the impacts of neurodegeneration.
How the study measured a tiny region’s big impact
The research combined functional brain imaging and physiological measures to investigate arousal, locus coeruleus activity, and attention. The study included 28 younger adults and 24 older adults. The team used pupil dilation as an external index of physiological arousal and locus coeruleus engagement, alongside fMRI to track activity across brain regions.
During the experiment, participants viewed pairs of images—one depicting a building and the other an object—where the visual contrast was manipulated so that sometimes the building image was clear and the object faint, and other times vice versa. On each trial, participants indicated which image appeared highlighted.
Some trials began with a tone signaling a possible electric shock at the end of the trial, creating higher physiological arousal, while other tones signaled no shock. Trials with the possible shock produced larger pupil dilation and increased sweat responses, confirming greater arousal.
Age-related disruption in network connectivity
In younger adults, anticipating a shock increased activity selectively in the parahippocampal place area when the building image was the salient target, and decreased activity when that image was non-salient. Functional connections between the locus coeruleus, the place area, and frontoparietal attention-control networks remained robust, enabling efficient suppression of irrelevant information under arousal.
In contrast, older adults displayed weaker functional connectivity between the locus coeruleus and frontoparietal attention networks when aroused. They also showed heightened place-area responses regardless of whether an image was salient, indicating a generalized increase in responsiveness to visual stimuli rather than the selective amplification seen in younger adults. In short, arousal increased the potential for distraction in older adults by reducing the network’s capacity to suppress non-salient inputs.
“Understanding how these network changes unfold with age may lead to interventions that preserve selective attention and reduce vulnerability to distraction and cognitive decline,” Mather said.
Co-authors include Tae-Ho Lee, Steven G. Greening, Allison Ponzio (USC), Taiji Ueno (Takachiho University), David Clewett (New York University), and Michiko Sakaki (University of Reading). The work received funding from the National Institute on Aging and grants from the Japan Society for the Promotion of Science and European funding agencies supporting related investigations into locus coeruleus function, attention, and aging.
Abstract
Arousal increases neural gain via the locus coeruleus–noradrenaline system in younger adults but not in older adults
This study shows that arousal sharpens attention in younger adults by amplifying salient information while suppressing non-salient input. Using a computational model and fMRI, the authors demonstrate that aging selectively impairs the suppression process under arousal: younger adults show increased processing of salient stimuli and decreased processing of non-salient stimuli, whereas older adults show heightened processing of both, reflecting greater excitatory responses to visual input and reduced functional connectivity between the locus coeruleus and frontoparietal networks. Consequently, arousal increases the likelihood of distraction in older adults.
Journal: Nature Human Behavior. Publication date: May 7, 2018. DOI: 10.1038/s41562-018-0344-1. Publisher summary adapted from university reporting. Image credited as public domain.