Abstract
Background: The hippocampus and its subfields (HippSub) are reported to be diminished in patients with Alzheimer's disease (AD), bipolar disorder (BD), and major depressive disorder (MDD). We examined these groups vs healthy controls (HC) to reveal HippSub alterations between diseases.Methods: We segmented 3T-MRI T2-weighted hippocampal images of 67 HC, 58 BD, and MDD patients from the AFFDIS study and 137 patients from the DELCODE study assessing cognitive decline, including subjective cognitive decline (SCD), amnestic mild cognitive impairment (aMCI), and AD, via Free Surfer 6.0 to compare volumes across groups.Results: Groups differed significantly in several HippSub volumes, particularly between patients with AD and mood disorders. In comparison to HC, significant lower volumes appear in aMCI and AD groups in specific subfields. Smaller volumes in the left presubiculum are detected in aMCI and AD patients, differing from the BD group. A significant linear regression is seen between left hippocampus volume and duration since the first depressive episode.Conclusions: HippSub volume alterations were observed in AD, but not in early-onset MDD and BD, reinforcing the notion of different neural mechanisms in hippocampal degeneration. Moreover, duration since the first depressive episode was a relevant factor explaining the lower left hippocampal volumes present in groups.
Highlights
The human hippocampus is known as a brain structure pivotal for memory formation
Participants were classified as having SCD in case of self-reported subjective cognitive decline and a neuropsychological test achievement superior than −1.5 standard deviation (SD) on each subtest of the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) test battery (Jessen et al, 2014, 2018, 2020)
Clinic and demographic data of study participants (n = 195) are presented in Table 1, showing sex, age, onset age of depressive episodes, number of depressive episodes, age at onset of condition, and duration since first depression compared across all groups (HC, SCD, amnestic mild cognitive impairment (aMCI), Alzheimer’s disease (AD), bipolar disorder (BD), and major depressive disorder (MDD))
Summary
The human hippocampus is known as a brain structure pivotal for memory formation. It is the plasticity of the hippocampus to form memory that makes it vulnerable to damage and volume reduction. HippSub fields are suitable biological imaging markers of early stages of AD, as the presubiculum-subiculum complex (Carlesimo et al, 2015; Jacobs et al, 2020), CA2– 3 (Hanseeuw et al, 2011), or CA1 region (de Flores et al, 2015) are often atrophied Supporting this idea, recent work indicates that lower subicular volumes in patients with memory impairment are related to the grade of ß-amyloid depositions independent of the presence of neurodegeneration assessed by fluorescence desoxyglucose positron emission tomography (FDG PET) (Filho et al, 2021). We examined these groups vs healthy controls (HC) to reveal HippSub alterations between diseases
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