Hippocampal acidity and volume are differentially associated with spatial navigation in older adults

The hippocampus is negatively affected by aging and is critical for spatial navigation. While there is evidence that wayfinding navigation tasks are especially sensitive to preclinical hippocampal deterioration, these studies have primarily used volumetric hippocampal imaging without considering microstructural properties or anatomical variation within the hippocampus. T1ρ is an MRI measure sensitive to regional pH, with longer relaxation rates reflecting acidosis as a marker of metabolic dysfunction and neuropathological burden. For the first time, we investigate how measures of wayfinding including landmark location learning and delayed memory in cognitively normal older adults (N = 84) relate to both hippocampal volume and T1ρ in the anterior and posterior hippocampus. Regression analyses revealed hippocampal volume was bilaterally related to learning, while right lateralized T1ρ was related to delayed landmark location memory and bilateral T1ρ was related to the delayed use of a cognitive map. Overall, results suggest hippocampal volume and T1ρ relaxation rate tap into distinct mechanisms involved in preclinical cognitive decline as assessed by wayfinding navigation, and laterality influenced these relationships more than the anterior-posterior longitudinal axis of the hippocampus.

Factors influencing developmental differences in retention of Pavlovian fear conditioning

Modern nonhuman animal research on the rapid forgetting of memories formed early in life-often termed "infantile amnesia"-has focused on neurobiological changes occurring between learning and retention testing to explain age differences in memory. Developmental differences in initial learning have received less attention as a contributing factor to infantile amnesia effects. The present study identifies conditions under which associative learning and memory are comparable between pre and postweaning rats across multiple training-testing intervals. Postnatal day (P) 17-18 or P24-25 littermates were trained with white noise conditional stimuli (CSs) alone, forward-paired, or explicitly unpaired with floor shock unconditional stimuli (USs), and tested for retention at intervals ranging between 5 min and 15 days later. Findings from within- and across-institution replications revealed that age differences in CS freezing were influenced by (a) the associative nature of the CS and US at training, (b) the number of CS, US presentations at training, and (c) the interval between training and testing. Rats trained on P17 or 18 displayed robust retention comparable to rats trained on P24 or 25 only when training in younger rats involved additional forward-paired CS-US presentations. Poor long-term retention observed at multiple training-testing intervals in rats trained on P17 or 18 was overcome with many additional forward-paired CS-US presentations at training. Conditions necessary for appropriate developmental comparisons of learning and memory relevant to the future neurobiological studies are discussed. (PsycInfo Database Record (c) 2021 APA, all rights reserved).