Allison Ponzio

Neuromelanin marks the spot: identifying a locus coeruleus biomarker of cognitive reserve in healthy aging

Leading a mentally stimulating life may build up a reserve of neural and mental resources that preserve cognitive abilities in late life. Recent autopsy evidence links neuronal density in the locus coeruleus (LC), the brains main source of norepinephrine, to slower cognitive decline before death, inspiring the idea that the noradrenergic system is a key component of reserve (Robertson, I. H. 2013. A noradrenergic theory of cognitive reserve: implications for Alzheimers disease. Neurobiol. Aging. 34, 298-308). Here, we tested this hypothesis using neuromelanin-sensitive magnetic resonance imaging to visualize and measure LC signal intensity in healthy younger and older adults. Established proxies of reserve, including education, occupational attainment, and verbal intelligence, were linearly correlated with LC signal intensity in both age groups. Results indicated that LC signal intensity was significantly higher in older than younger adults and significantly lower in women than in men. Consistent with the LC-reserve hypothesis, both verbal intelligence and a composite reserve score were positively associated with LC signal intensity in older adults. LC signal intensity was also more strongly associated with attentional shifting ability in older adults with lower cognitive reserve. Together these findings link in vivo estimates of LC neuromelanin signal intensity to cognitive reserve in normal aging.

Hearing something emotional influences memory for what was just seen: How arousal amplifies effects of competition in memory consolidation

Enhanced memory for emotional items often comes at the cost of memory for the background scenes. Because emotional foreground items both induce arousal and attract attention, it is not clear whether the emotion effects are simply the result of shifts in visual attention during encoding or whether arousal has effects beyond simple attention capture. In the current study, participants viewed a series of scenes that each either had a foreground object or did not have one, and then, after each image, heard either an emotionally arousing negative sound or a neutral sound. After a 24-hr delay, they returned for a memory test for the objects and scenes. Postencoding arousal decreased recognition memory of scenes shown behind superimposed objects but not memory of scenes shown alone. These findings support the hypothesis that arousal amplifies the effects of competition between mental representations, influencing memory consolidation of currently active representations.

Higher locus coeruleus MRI contrast is associated with lower parasympathetic influence over heart rate variability

Abstract The locus coeruleus (LC) is a key node of the sympathetic nervous system and suppresses parasympathetic activity that would otherwise increase heart rate variability. In the current study, we examined whether LC‐MRI contrast reflecting neuromelanin accumulation in the LC was associated with high‐frequency heart rate variability (HF‐HRV), a measure reflecting parasympathetic influences on the heart. Recent evidence indicates that neuromelanin, a byproduct of catecholamine metabolism, accumulates in the LC through young and mid adulthood, suggesting that LC‐MRI contrast may be a useful biomarker of individual differences in habitual LC activation. We found that, across younger and older adults, greater LC‐MRI contrast was negatively associated with HF‐HRV during fear conditioning and spatial detection tasks. This correlation was not accounted for by individual differences in age or anxiety. These findings indicate that individual differences in LC structure relate to key cardiovascular parameters. HighlightsWe measured locus coeruleus neuromelanin MRI contrast (LC‐MRI).Participants with higher LC‐MRI had lower high‐frequency heart rate variability.This relationship was not due to individual differences in age or anxiety.

The Effects of Emotion Regulation on Explicit Memory Depend on Strategy and Testing Method

Although previous work has shown that emotion regulation strategies can influence memory, the mechanisms through which different strategies produce different memory outcomes are not well understood. We examined how two cognitive reappraisal strategies with similar elaboration demands but diverging effects on visual attention and emotional arousal influenced explicit memory for emotional stimuli and for the strategies used to evaluate the stimuli. At encoding, participants used reappraisal to increase and decrease the personal relevance of neutral and emotional pictures. In two experiments, recall accuracy was highest for emotional pictures featured on increase trials, intermediate for emotional pictures featured on look (respond naturally) trials, and lowest for emotional pictures featured on decrease trials. This recall pattern emerged after a short delay (15 min) and persisted over a longer delay (48 hr). Memory accuracy for the strategies used to evaluate the pictures showed a different pattern: Strategy memory was better for emotional pictures featured on decrease and increase trials than for pictures featured on look trials. Our findings show that the effects of emotion regulation on memory depend both on the particular strategy engaged and the particular aspect of memory being tested.

Arousal increases neural gain via the locus coeruleus–noradrenaline system in younger adults but not in older adults

In younger adults, arousal amplifies attentional focus to the most salient or goal-relevant information while suppressing other information. A computational model of how the locus coeruleus–noradrenaline system can implement this increased selectivity under arousal and a functional magnetic resonance imaging (fMRI) study comparing how arousal affects younger and older adults’ processing indicate that the amplification of salient stimuli and the suppression of non-salient stimuli are separate processes, with ageing affecting suppression without affecting amplification under arousal. In the fMRI study, arousal increased processing of salient stimuli and decreased processing of non-salient stimuli for younger adults. By contrast, for older adults, arousal increased processing of both low- and high-salience stimuli, generally increasing excitatory responses to visual stimuli. Older adults also showed a decline in locus coeruleus functional connectivity with frontoparietal networks that coordinate attentional selectivity. Thus, among older adults, arousal increases the potential for distraction from non-salient stimuli.High arousal enables young people to better detect salient stimuli. In older people, arousal leads to increased processing of all stimuli. This difference can be explained by age-related changes in how the locus coeruleus–noradrenaline system interacts with cortical attention networks.

Dedifferentiation of emotion regulation strategies in the aging brain

Different emotion regulation strategies are distinctly represented in the brains of younger adults. Decreasing a reaction to a negative situation by reinterpreting it (reappraisal) relies on cognitive control regions in the prefrontal cortex, while distracting away from a stressor involves more posterior medial structures. In this study, we used Multi-Voxel pattern analyses (MVPA) to examine whether reappraisal and distraction strategies have distinct representations in the older adult brain, or whether emotion regulation strategies become more dedifferentiated in later life. MVPA better differentiated the two emotion regulation strategies for younger adults than for older adults, and revealed the greatest age-related differences in differentiation in the posterior medial cortex (PMC). Univariate analyses revealed equal PMC recruitment across strategies for older adults, but greater activity during distraction than reappraisal for younger adults. The PMC is central to self-focused processing, and thus our findings are consistent with the possibility that focusing on the self may be a default mechanism across emotion regulation strategies for older people.