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PurposeIn vivo measurement of the spatial distribution of neurofibrillary tangle pathology is critical for early diagnosis and disease monitoring of Alzheimer's disease (AD).MethodsForty-nine participants were scanned with 18F-PI-2620 PET to examine the distribution of this novel PET ligand throughout the course of AD: 36 older healthy controls (HC) (age range 61 to 86), 11 beta-amyloid+ (Aβ+) participants with cognitive impairment (CI; clinical diagnosis of either mild cognitive impairment or AD dementia, age range 57 to 86), and 2 participants with semantic variant primary progressive aphasia (svPPA, age 66 and 78). Group differences in brain regions relevant in AD (medial temporal lobe, posterior cingulate cortex, and lateral parietal cortex) were examined using standardized uptake value ratios (SUVRs) normalized to the inferior gray matter of the cerebellum.ResultsSUVRs in target regions were relatively stable 60 to 90 min post-injection, with the exception of very high binders who continued to show increases over time. Robust elevations in 18F-PI-2620 were observed between HC and Aβ+ CI across all AD regions. Within the HC group, older age was associated with subtle elevations in target regions. Mildly elevated focal uptake was observed in the anterior temporal pole in one svPPA patient.ConclusionPreliminary results suggest strong differences in the medial temporal lobe and cortical regions known to be impacted in AD using 18F-PI-2620 in patients along the AD trajectory. This work confirms that 18F-PI-2620 holds promise as a tool to visualize tau aggregations in AD.

Background: Olfactory deficiency can be present in preclinical Alzheimer's (AD) and Parkinson's disease (PD), predicting their subsequent manifestation, including mild cognitive impairment (MCI). Analyzing key regions within the olfactory circuit could reveal important insights into the neuropathological progression. Dysfunction in the olfactory circuit has been shown in the olfactory nerve in limited postmortem studies, including involvement of a key region, the piriform cortex. FDG‐positron emission tomography (PET) and fMRI have shown differential and reduced piriform cortex metabolism/activation in AD. Thus, the piriform cortex is a promising candidate in the early identification of neurodegenerative pathology underlying olfaction. We used tau MR‐PET to analyze the piriform cortex, in comparison to the adjacent medial temporal lobe. Method: We analyzed 115 subjects: 23 were excluded (incomplete data), leaving 31 amyloid‐negative and 25 amyloid‐positive healthy controls, 8 MCI, 15 AD, and 13 PD. All subjects underwent MR‐PET using tau tracer PI‐2620 with a simultaneous coregistered sagittal T1‐weighted 3D IR‐FSPGR and a simultaneous/recently acquired coronal T2‐weighted FSE. Automatic Segmentation of Hippocampal Subfields was performed, including the entorhinal‐perirhinal cortices (Fig. 1D‐F). Referencing published piriform segmentation guidelines, we manually segmented blind to subject diagnosis the frontal/temporal portions of the piriform cortex (Fig. 1C), including multiple independent quality control checks. As tau distributions appeared non‐normal among the five ordinal patient categories (Amyloid–HC, Amyloid+HC, MCI, AD, Normal PD), we used a nonparametric Jonckheere‐Terpstra test in Stata to test for ordinal increase in tau uptake across four regions bilaterally (whole hippocampus = CA1‐4 + DG + subiculum, entorhinal‐perirhinal, amygdala, and piriform). Result: We found an ordinal increase in piriform tau uptake with increasing disease severity (amyloid‐negative controls, amyloid‐positive controls, MCI and AD) (Figure 2A‐D). Amyloid‐positive controls showed significantly greater uptake than amyloid‐negative controls. Piriform uptake was not elevated in cognitively unimpaired PD compared to Amyloid‐HC. Piriform volume was statistically equivalent across groups, except PD had lower volumes (Figure 2E‐H). Negative correlations were present between memory performance and piriform uptake (Figure 3). Conclusion: Cross‐sectionally, there is an early increase in tau uptake in the piriform cortex in AD but not in PD. [ABSTRACT FROM AUTHOR]

The thalamic nuclei are thought to play a critical role in recognition memory. Specifically, the anterior thalamic nuclei and medial dorsal nuclei may serve as critical output structures in distinct hippocampal and perirhinal cortex systems, respectively. Existing evidence indicates that damage to the anterior thalamic nuclei leads to impairments in hippocampal-dependent tasks. However, evidence for the opposite pattern following medial dorsal nuclei damage has not yet been identified. In the present study, we investigated recognition memory in NC, a patient with relatively selective medial dorsal nuclei damage, using two object recognition tests with similar foils: a yes/no (YN) test that requires the hippocampus, and a forced choice corresponding test (FCC) that is supported by perirhinal cortex. NC performed normally in the YN test, but was impaired in the FCC test. Critically, FCC performance was impaired only when the study-test delay period was filled with interference. We interpret these results in the context of the representational-hierarchical model, which predicts that memory deficits following damage to the perirhinal system arise due to increased vulnerability to interference. These data provide the first evidence for selective deficits in a task that relies on perirhinal output following damage to the medial dorsal nuclei, providing critical evidence for dissociable thalamic contributions to recognition memory.

In a Yes/No object recognition memory test with similar lures, older adults typically exhibit elevated rates of false recognition. However, the contributions of impaired retrieval, relative to reduced availability of target details, are difficult to disentangle using such a test. The present investigation sought to decouple these factors by comparing performance on a Yes/No (YN) test to that on a Forced Choice (FC) test, which minimizes demands on strategic retrieval processes, enabling a more direct measure of the availability of object details. Older adults exhibited increased lure false recognition across test formats (Experiment 1), suggesting a decline in the availability of object details contributes to deficits in performance. Manipulating interference by varying the number of objects studied selectively enhanced performance in the FC test, resulting in matched performance across groups, whereas age differences in YN performance persisted (Experiment 2), indicating an additional contribution of impaired strategic retrieval. Consistent with differential sensitivity of test format to strategic retrieval and the quality of stimulus representations among older adults, variability in the quality of object representations, measured using a perceptual discrimination task, was selectively related to FC performance. In contrast, variability in memory control processes, as measured with tests of recall and executive function, was related to performance across test formats. These results suggest that both declines in the availability of object details and impaired retrieval of object details contribute to elevated rates of lure false recognition with age, and highlight the utility of test format for dissociating these factors in memory-impaired populations.

INTRODUCTION: In this study, we leverage proteomic techniques to identify communities of proteins underlying Alzheimer's disease (AD) risk among clinically unimpaired (CU) older adults. METHODS: We constructed a protein co‐expression network using 3869 cerebrospinal fluid (CSF) proteins quantified by SomaLogic, Inc., in a cohort of participants along the AD clinical spectrum. We then replicated this network in an independent cohort of CU older adults and related these modules to clinically‐relevant outcomes. RESULTS: We discovered modules enriched for phosphorylation and ubiquitination that were associated with abnormal amyloid status, as well as p‐tau181 (M4: β = 2.44, p < 0.001, M7: β = 2.57, p < 0.001) and executive function performance (M4: β = −2.00, p = 0.005, M7: β = −2.39, p < 0.001). DISCUSSION: In leveraging CSF proteomic data from individuals spanning the clinical spectrum of AD, we highlight the importance of post‐translational modifications for early cognitive and pathological changes. [ABSTRACT FROM AUTHOR]

Introduction: The availability of amyloid beta (Aβ) targeting therapies for Alzheimer's disease (AD) is increasing the demand for scalable biomarkers that are sensitive to early cerebral Aβ accumulation., Methods: We evaluated fully-automated Lumipulse plasma Aβ 42 /Aβ 40 immunoassays for detecting cerebral Aβ in 457 clinically unimpaired (CU) and clinically impaired (CI) Stanford Alzheimer's Disease Research Center (Stanford ADRC) participants and 186 CU in the Stanford Aging and Memory Study (SAMS). Longitudinal change in ADRC plasma Aβ 42 /Aβ 40 and cognition and cross-sectional associations with SAMS memory and tau positron emission tomography (PET) were examined., Results: Plasma Aβ 42 /Aβ 40 exhibited high performance in detecting amyloid positivity defined by PET (area under the curve [AUC]: 0.885, 95% confidence interval [CI]: 0.816-0.955). Once abnomal, plasma Aβ 42 /Aβ 40 remained low and predicted cognitive decline in both CU and CI individuals. Among SAMS CU, plasma Aβ 42 /Aβ 40 was associated with poorer hippocampal-dependent memory and elevated tau accumulation., Discussion: Lumipulse plasma Aβ 42 /Aβ 40 is a scalable assay for detection of cerebral Aβ and prediction of risk for cognitive decline across the AD continuum., Highlights: Lumipulse plasma amyloid beta (Aβ) 42 /Aβ 40 exhibited high accuracy in detecting amyloid positivity. Plasma amyloid-positive (Aβ+) individuals exhibited stability of Aβ 42 /Aβ 40 over time. Plasma Aβ 42 /Aβ 40 predicted future cognitive decline across the Alzheimer's disease (AD) spectrum. Plasma Aβ 42 /Aβ 40 was sensitive to memory and tau burden in clinically unimpaired older adults., (© 2024 The Author(s). Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Human aging affects the ability to remember new experiences, in part, because of altered neural function during memory formation. One potential contributor to age-related memory decline is diminished neural selectivity -- i.e., a decline in the differential response of cortical regions to preferred vs. non-preferred stimuli during event perception -- yet the factors driving variability in neural selectivity with age remain unclear. We examined the impact of top-down attention and preclinical Alzheimer's disease (AD) pathology on neural selectivity during memory encoding in 156 cognitively unimpaired older participants who underwent fMRI while performing a word-face and word-scene associative memory task. Neural selectivity in face- and place-selective cortical regions was greater during events that were later remembered compared to forgotten. Critically, neural selectivity during learning positively scaled with memory-related variability in top-down attention, whereas selectivity negatively related to early AD pathology, evidenced by elevated plasma pTau 181 . Path analysis revealed that neural selectivity at encoding mediated the effects of age, top-down attention, and pTau 181 on associative memory. Collectively, these data reveal multiple pathways that contribute to memory differences among older adults -- AD-independent reductions in top-down attention and AD-related pathology alter the precision of cortical representations of events during experience, with consequences for remembering., Competing Interests: Competing interests: The authors declare no compete of interests.

Introduction: In this study, we leverage proteomic techniques to identify communities of proteins underlying Alzheimer's disease (AD) risk among clinically unimpaired (CU) older adults., Methods: We constructed a protein co-expression network using 3869 cerebrospinal fluid (CSF) proteins quantified by SomaLogic, Inc., in a cohort of participants along the AD clinical spectrum. We then replicated this network in an independent cohort of CU older adults and related these modules to clinically-relevant outcomes., Results: We discovered modules enriched for phosphorylation and ubiquitination that were associated with abnormal amyloid status, as well as p-tau 181 (M4: β = 2.44, p < 0.001, M7: β = 2.57, p < 0.001) and executive function performance (M4: β = -2.00, p = 0.005, M7: β = -2.39, p < 0.001)., Discussion: In leveraging CSF proteomic data from individuals spanning the clinical spectrum of AD, we highlight the importance of post-translational modifications for early cognitive and pathological changes., (© 2023 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)