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51 Pupillary Responses During Verbal Fluency Tasks as a Biomarker of Risk for Alzheimer's Disease
- Veronica Gandara, Mark Bondi, Jeremy Elman, William Kremen, David Salmon, Jason Holden, Alexandra Weigand, Seraphina Solders, Peter Link, Eric Granholm
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- Journal:
- Journal of the International Neuropsychological Society / Volume 29 / Issue s1 / November 2023
- Published online by Cambridge University Press:
- 21 December 2023, pp. 258-259
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Objective:
We examined the use of pupillometry as an early risk marker of Alzheimer's disease (AD). Pupil dilation during a cognitive task has been shown to be an index of cognitive effort and may provide a marker of early change in cognition even before performance begins to decline. Individuals who require more effort to successfully perform a task may be closer to decline. We previously found greater compensatory effort to perform the digit span task in individuals with amnestic mild cognitive impairment (aMCI) who may be at greater risk for AD than individuals with non-amnestic MCI (naMCI). Task evoked pupil dilation is linked to increased norepinephrine output from the locus coeruleus (LC), a structure affected early in the AD pathological process. In this study, we measured pupil dilation during verbal fluency tasks in participants with aMCI or naMCI, and cognitively normal (CN) individuals. Based on our findings using the digit span task, we hypothesized that participants with aMCI would show greater compensatory cognitive effort than the other two groups.
Participants and Methods:This study included 101 older adults without dementia recruited from the UC San Diego Shiley-Marcos Alzheimer's Disease Research Center and San Diego community (mean [SD] age = 74.7 [5.8]; education = 16.6 [2.5]; N=58 female; N=92 White); 62 CN, 20 aMCI and 19 naMCI participants. Pupillary responses (change relative to baseline at the start of each trial) were recorded at 30 Hz using a Tobii X2-30 (Tobii, Stockholm, Sweden) during semantic (animals, fruits, vegetables) and phonemic (letters F, A, S) fluency tasks. Participants generated as many words as possible in a category (semantic) or starting with a given letter (phonemic) in 60 seconds.
Results:Repeated measures ANOVA (3 groups X 2 fluency conditions) with age, education and sex as covariates showed a significant main effect of group (F(2,95)=3.64, p=.03), but no group X condition interaction (F<1). Pairwise comparisons showed significantly greater fluency task-evoked dilation for aMCI relative to CN (p=.015) and naMCI (p=.019) participants. When controlling for performance (total letter or category words produced), pupil dilation (cognitive effort) remained significantly greater in aMCI relative to the other two groups in both fluency conditions, suggesting pupil dilation informs risk beyond information provided by task performance.
Conclusions:In a previous sample of community-dwelling men who were an average of 13 years younger than the present sample, we found significantly greater pupil dilation during a digit span task in aMCI relative to naMCI and CN groups. In the present study, we replicated those findings in an older sample using a different cognitive task. Significantly greater pupil dilation was found in individuals with aMCI on verbal fluency tasks, indicating greater compensatory cognitive effort to maintain performance. Pupillometry provides a promising biomarker that might be used as an inexpensive and noninvasive additional screening tool for risk of AD.
10 Pupil Dilation During the Stroop Task Offers a Sensitive and Scalable Biomarker of Locus Coeruleus Integrity
- Alexandra J Weigand, Jeremy A Elman, Seraphina K Solders, Alyssa J Macomber, Lawrence R Frank, Eric L Granholm, Mark W Bondi
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- Journal:
- Journal of the International Neuropsychological Society / Volume 29 / Issue s1 / November 2023
- Published online by Cambridge University Press:
- 21 December 2023, pp. 802-803
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Objective:
Neuronal dysfunction of the locus coeruleus (LC), the primary producer of norepinephrine, has been identified as a biomarker of early Alzheimer's disease (AD) pathophysiology. Norepinephrine has been implicated in attentional control, and its reduced cortical circulation in AD may be associated with selective attentional difficulties. Additionally, greater pupil dilation indicates greater effort needed to perform a cognitive task, and greater compensatory effort to perform the digit span task has been found in individuals at risk for AD. In this study, we examined associations between a neuroimaging biomarker of the LC and pupil dilation during the Stroop task as a sensitive measure of attentional control.
Participants and Methods:64 older adults without dementia were recruited from the San Diego community (mean [SD] age = 74.3 [6.3]; 39 cognitively unimpaired and 25 with mild cognitive impairment). All participants underwent magnetic resonance imaging of the LC and generated behavioral data from a computerized Stroop task that included 36 incongruent trials (e.g., GREEN presented in red ink), 36 congruent trials (e.g., GREEN presented in green ink), and 32 neutral trials (e.g., LEGAL presented in green ink) in a randomized presentation. Mean pupil dilation for each trial (change relative to baseline at the start of each trial) was measured at 30 Hz using the Tobii X2-30 system (Tobii, Stockholm, Sweden) and averaged within each Stroop condition. Paired t-tests assessed for differences in mean pupil dilation across incongruent and congruent Stroop conditions. Iterative re-weighted least squares regression was used to assess the association between a rostral LC contrast ratio measure derived from manually marked ROIs and mean pupil dilation during incongruent trials divided by congruent trials, adjusting for age, sex, and education. Follow-up analyses also assessed the association of these variables with mean reaction time (RT) for incongruent trials divided by congruent trials.
Results:Mean pupil dilation significantly differed across conditions (t = 3.74, mean difference = .13, 95% CI [.06, .20]) such that dilation was higher during the incongruent condition (mean [SD] dilation = .18 [.38] mm) relative to the congruent condition (mean [SD] dilation = .05 [.35] mm). A significant association was observed between pupil dilation and LC contrast ratio, such that increased levels of mean dilation during incongruent trials relative to congruent trials were observed at lower levels of LC contrast ratio (i.e., lower LC integrity; r = -.37, 95% CI [-.55, -.13]). This association was not observed for mean dilation during only congruent trials (r = -.08, 95% CI [-.31, .18]). Additionally, neither LC contrast ratio [r = .24, 95% CI [-.02, .46]) nor mean incongruent/congruent pupil dilation (r = .14, 95% CI [-.13, .37]) were associated with incongruent/congruent RT.
Conclusions:Findings suggest that increased pupil dilation during a demanding attentional task is indicative of increased compensatory effort needed to achieve the same level of performance for individuals with reduced LC biomarker integrity. Pupillometry assessment offers a low-cost, non-invasive, and scalable biomarker of LC dysfunction that may be indicative of preclinical AD.
49 Locus Coeruleus MR Signal Interacts with CSF p-tau/AB42 to Predict Attention, Executive Function, and Verbal Memory
- Seraphina K Solders, Tamara R Shabi, Alexandra J Weigand, Jeremy A Elman, Eric L Granholm, Lawrence R Frank, Mark W Bondi
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- Journal:
- Journal of the International Neuropsychological Society / Volume 29 / Issue s1 / November 2023
- Published online by Cambridge University Press:
- 21 December 2023, pp. 921-922
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Objective:
The locus coeruleus (LC) plays a key role in cognitive processes such as attention, executive function, and memory. The LC has been identified as an early site of tau accumulation in Alzheimer’s disease (AD). LC neurons are thought to survive, albeit with limited functionality, until later stages of the disease, though how exactly this limited functionality impacts cognition through the course of AD is still poorly understood. We investigated the interactive effects of an imaging biomarker of the LC and AD-related cerebrospinal fluid (CSF) biomarkers on attention, executive function, and memory.
Participants and Methods:We recruited 67 older adults from the San Diego community (mean age=74.52 years; 38 cognitively normal, 23 with mild cognitive impairment, and 6 with probable AD). Participants had LC-sensitive magnetic resonance imaging (MRI) used to obtain a measure of LC signal relative to surrounding tissue, with lower LC signal possibly indicating limited functionality. Participants also underwent a lumbar puncture to obtain CSF measurements of amyloid-beta 42 (Ab42) and phosphorylated tau (p-tau). We calculated the p-tau/Ab42 ratio, which is positively correlated with AD progression. Finally, participants were administered a comprehensive neuropsychological battery, and cognitive composites were created for attention (Digit Symbol, Digit Span Forward, Trails A), executive function (Digit Span Backward, Trails B, Color-Word Inhibition Switching), and two measures of verbal memory [learning (CVLT List A 1-5, Logical Memory Immediate Recall) and delay (CVLT Long Free Recall, Logical Memory Delayed Recall)]. Four multiple linear regressions modeled the relationship between each composite with age, gender, education, p-tau/Ab42, average LC contrast, and interactions between average LC contrast and p-tau/Ab42. For models that were statistically significant, additional regressions were assessed to determine which segment of the LC (caudal, middle, rostral) contributed to the relationship.
Results:Our model predicted attention (p=.001, R2=.298) with main effects of average LC signal, p-tau/Ab42, and LC by p-tau/Ab42 interaction. Follow-up regressions revealed that each LC segment contributes to this relationship. Our model predicted executive function (p=.006, R2=.262) with a main effect of average LC signal and LC by p-tau/Ab42 interaction. Follow-up regressions revealed that this relationship was limited to the caudal and middle LC. Our models predicted both verbal learning (p<.001, R2=.512) and delayed memory (p<.001, R2=.364); both with main effects of gender and education. Follow-up regressions revealed that the rostral LC signal interacts with p-tau/Ab42 to predict both verbal learning and delayed memory. For all interactions, those with low p-tau/Ab42 exhibited a positive relationship between LC signal and cognition, whereas those with higher p-tau/Ab42 showed a negative relationship.
Conclusions:MR-assessed LC signal relates to attention, executive function, and verbal learning and memory in a manner that depends on CSF levels of p-tau and Ab42. The relationship between LC signal and cognition is positive at low levels and negative at higher levels of p-tau/Ab42. If lower LC signal indicates reduced integrity, these findings imply that MR-assessed LC signal may be a more meaningful marker of AD progression in earlier stages of the disease. Alternatively, this measure may capture a different underlying mechanism depending on tau and amyloid biomarker status.