Evidence of Impaired Remote Experience-near Semantic Memory in Medial Temporal Lobe Amnesia

Neuropsychological research suggests that "experience-near" semantic memory, meaning knowledge attached to a spatiotemporal or event context, is commonly impaired in individuals who have medial temporal lobe amnesia. It is not known if this impairment extends to remotely acquired experience-near knowledge, which is a question relevant to understanding hippocampal/medial temporal lobe functioning. In the present study, we administered a novel semantic memory task designed to target knowledge associated with remote, "dormant" concepts, in addition to knowledge associated with active concepts, to four individuals with medial temporal lobe amnesia and eight matched controls. We found that the individuals with medial temporal lobe amnesia generated significantly fewer experience-near semantic memories for both remote concepts and active concepts. In comparison, the generation of abstract or "experience-far" knowledge was largely spared in the individuals with medial temporal lobe amnesia, regardless of whether the targets for retrieval were remote or active concepts. We interpret these findings as evidence that the medial temporal lobes may have a sustained role in the retrieval of semantic memories associated with spatiotemporal and event contexts, which are cognitive features often ascribed to episodic memory. These results align with recent theoretical models proposing that the hippocampus/medial temporal lobes support cognitive processes that are involved in, but not exclusive to, episodic memory. © 2023 Massachusetts Institute of Technology.3 month embargo; published 1 December 2023This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Characterization of Bi4Ge3O12 single crystal by impedance spectroscopy

Bi4Ge3O12 (bismuth germanate - BGO) single crystals were produced by the Czochralski technique and their electrical and dielectric properties were investigated by impedance spectroscopy. The isothermal ac measurements were performed for temperatures from room temperature up to 750 °C, but only the data taken above 500 °C presented a complete semicircle in the complex impedance diagrams. Experimental data were fitted to a parallel RC equivalent circuit, and the electrical conductivity was obtained from the resistivity values. Conductivity values from 5.4 × 10(9) to 4.3 × 10-7 S/cm were found in the temperature range of 500 to 750 °C. This electrical conductivity is thermally activated, following the Arrhenius law with an apparent activation energy of (1.41 ± 0.04) eV. The dielectric properties of BGO single crystal were also studied for the same temperature interval. Permittivity values of 20 ± 2 for frequencies higher than 10³ Hz and a low-frequency dispersion were observed. Both electric and dielectric behavior of BGO are typical of systems in which the conduction mechanism dominates the dielectric response

What should be considered in using standard knee radiographs to estimate mechanical alignment of the knee?

Objective: Anatomical tibiofemoral angle (anatomical TFA) of the knee measured on standard knee radiographs is still widely used as proxy for mechanical tibiofemoral angle (mechanical TFA), because of the practical and economic limitations in using full-limb radiographs. However, reported differences between anatomical and mechanical TFAs show wide variations. The first aim of this study was to determine whether gender, the presence of advanced osteoarthritis (OA), and history of total knee arthroplasty (TKA) influence the differences between anatomical and mechanical TFAs. The second aim was to identify anatomical features that cause divergences between anatomical and mechanical TFAs, and the final aim was to determine whether anatomical TFA measured using reference points more distant from the knee provides more accurate estimates of mechanical TFA. Design: In 102 knees with advanced OA before and after TKAs and 99 control knees with no/minimal OA, we assessed the differences between two anatomical TFAs, namely, anatomical TFA1 and anatomical TFA2, which were based on conventional or more distant proximal and distal reference points on standard knee radiographs, respectively, and the mechanical TFA measured on full-limb radiographs. These differences were investigated for women vs men, no/minimal OA vs advanced OA, and for knees before vs after TKA. Regression analyses were performed to determine associations between femoral and tibial anatomical characteristics and the differences between mechanical and anatomical TFAs. Results: The OA group showed significantly greater differences between mechanical and anatomical TFAs than the control group for both genders. In OA and TKA group, women were more likely to have greater mean differences between mechanical and anatomical TFAs than men. However, TKA did not significantly affect these differences. Femoral and tibial bowing angles, particularly of the femur, were found to be the major contributors to divergences between mechanical and two anatomical TFAs. Furthermore, anatomical TFA2 was found to provide more accurate estimates of mechanical TFA. Conclusions: We found that the differences between mechanical and anatomical TFAs depend on gender and the presence of advanced OA, but not on a history of TKA. These findings indicate that prediction of mechanical TFA based on anatomical TFA is dependent on study population characteristics. This study also shows that the presence of lateral bowing of the femur is a major cause of mechanical TFA to anatomical TFA variations associated with gender and advanced OA. To reduce the adverse effects of anatomical variations on estimations of mechanical TFA based on an anatomical TFA method, more distant proximal and distal reference points are recommended to determine anatomical TFA value on standard knee radiographs. (C) 2010 Osteoarthritis Research Society International. Published by Elsevier Ltd. 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