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Objective: Alzheimer's disease (AD) is a major health concern for aging adults with Down syndrome (DS), but conventional diagnostic techniques are less reliable in those with severe baseline disability. Likewise, acquisition of magnetic resonance imaging to evaluate cerebral atrophy is not straightforward, as prolonged scanning times are less tolerated in this population. Computed tomography (CT) scans can be obtained faster, but poor contrast resolution limits its function for morphometric analysis. We implemented an automated analysis of CT scans to characterize differences across dementia stages in a cross‐sectional study of an adult DS cohort. Methods: CT scans of 98 individuals were analyzed using an automatic algorithm. Voxel‐based correlations with clinical dementia stages and AD plasma biomarkers (phosphorylated tau‐181 and neurofilament light chain) were identified, and their dysconnectomic patterns delineated. Results: Dementia severity was negatively correlated with gray (GM) and white matter (WM) volumes in temporal lobe regions, including parahippocampal gyri. Dysconnectome analysis revealed an association between WM loss and temporal lobe GM volume reduction. AD biomarkers were negatively associated with GM volume in hippocampal and cingulate gyri. Interpretation: Our automated algorithm and novel dysconnectomic analysis of CT scans successfully described brain morphometric differences related to AD in adults with DS, providing a new avenue for neuroimaging analysis in populations for whom magnetic resonance imaging is difficult to obtain. [ABSTRACT FROM AUTHOR]

Introduction: Hippocampal sclerosis of aging (HS) is an important component of combined dementia neuropathology. However, the temporal evolution of its histologically‐defined features is unknown. We investigated pre‐mortem longitudinal hippocampal atrophy associated with HS, as well as with other dementia‐associated pathologies. Methods: We analyzed hippocampal volumes from magnetic resonance imaging (MRI) segmentations in 64 dementia patients with longitudinal MRI follow‐up and post‐mortem neuropathological evaluation, including HS assessment in the hippocampal head and body. Results: Significant HS‐associated hippocampal volume changes were observed throughout the evaluated timespan, up to 11.75 years before death. These changes were independent of age and Alzheimer's disease (AD) neuropathology and were driven specifically by CA1 and subiculum atrophy. AD pathology, but not HS, was associated significantly with the rate of hippocampal atrophy. Discussion: HS‐associated volume changes are detectable on MRI earlier than 10 years before death. Based on these findings, volumetric cutoffs could be derived for in vivo differentiation between HS and AD. HIGHLIGHTS: Hippocampal atrophy was found in HS+ patients earlier than 10 years before death.These early pre‐mortem changes were driven by reduced CA1 and subiculum volumes.Rates of hippocampus and subfield volume decline were independent of HS.In contrast, steeper atrophy rates were associated with AD pathology burden.Differentiation between AD and HS could be facilitated based on these MRI findings. [ABSTRACT FROM AUTHOR]

Responding to threat is under strong survival pressure, promoting the evolution of systems highly optimized for the task. Though the amygdala is implicated in 'detecting' threat, its role in the action that immediately follows—'orienting'—remains unclear. Critical to mounting a targeted response, such early action requires speed, accuracy, and resilience optimally achieved through conserved, parsimonious, dedicated systems, insured against neural loss by a parallelized functional organization. These characteristics tend to conceal the underlying substrate not only from correlative methods but also from focal disruption over time scales long enough for compensatory adaptation to take place. In a study of six patients with intracranial electrodes temporarily implanted for the clinical evaluation of focal epilepsy, we investigated gaze orienting to fear during focal, transient, unilateral direct electrical disruption of the amygdala. We showed that the amygdala is necessary for rapid gaze shifts towards faces presented in the contralateral hemifield regardless of their emotional expression, establishing its functional lateralization. Behaviourally dissociating the location of presented fear from the direction of the response, we implicated the amygdala not only in detecting contralateral faces, but also in automatically orienting specifically towards fearful ones. This salience-specific role was demonstrated within a drift-diffusion model of action to manifest as an orientation bias towards the location of potential threat. Pixel-wise analysis of target facial morphology revealed scleral exposure as its primary driver, and induced gamma oscillations—obtained from intracranial local field potentials—as its time-locked electrophysiological correlate. The amygdala is here reconceptualized as a functionally lateralized instrument of early action, reconciling previous conflicting accounts confined to detection, and revealing a neural organisation analogous to the superior colliculus, with which it is phylogenetically kin. Greater clarity on its role has the potential to guide therapeutic resection, still frequently complicated by impairments of cognition and behaviour related to threat, and inform novel focal stimulation techniques for the management of neuropsychiatric conditions. [ABSTRACT FROM AUTHOR]