Episodic memory reconsolidation and strengthening

Episodic memories are not always accurate, subject to false recollection due to the process of memory reconsolidation (Loftus, 2005). Memory reactivation places memory to a labile state and can lead to two phenomena: memory updating/reconsolidation with possibility of having inaccurate memories (Hupbach et al. 2007) and memory strengthening. By replicating Hupbach et al. (2007, 2008) study, Study 1 aimed to investigate the impact of music upon memory reconsolidation whereas Study 2 explored whether exposure to original learning context is sufficient to trigger reconsolidation. Study 1 found out that reconsolidation process may not be as reliable as suggested in existing reconsolidation studies. Study 2 discovered dissociation between updating of list memory and resistance to the memory-weakening effect of interference, suggesting reactivation-induced reconsolidation can maintain or even strengthen memories. Study 3 tested directly the capacity of memory reactivation to facilitate memory strengthening. An idea of implementing 6 hours interval in between Day 2 sessions was suggested, aimed to determine whether or not the learning effect is mediated by reconsolidation processes. The common effects of retrieval-relearning, relearning-retrieval, relearning-relearning, retrieval-6 hours-relearning, relearning-6 hours-retrieval to strengthen episodic memory may reflect different underlying processes, one or more of which might be related to memory reconsolidation

Postretrieval Relearning Strengthens Hippocampal Memories via Destabilization and Reconsolidation.

Memory reconsolidation is hypothesized to be a mechanism by which memories can be updated with new information. Such updating has previously been shown to weaken memory expression or change the nature of the memory. Here we demonstrate that retrieval-induced memory destabilization also allows that memory to be strengthened by additional learning. We show that for rodent contextual fear memories, this retrieval conditioning effect is observed only when conditioning occurs within a specific temporal window opened by retrieval. Moreover, it necessitates hippocampal protein degradation at the proteasome and engages hippocampal Zif268 protein expression, both of which are established mechanisms of memory destabilization-reconsolidation. We also demonstrate a conceptually analogous pattern of results in human visual paired-associate learning. Retrieval-relearning strengthens memory performance, again only when relearning occurs within the temporal window of memory reconsolidation. These findings link retrieval-mediated learning in humans to the reconsolidation literature, and have potential implications both for the understanding of endogenous memory gains and strategies to boost weakly learned memories

Drumhead Surface States and Topological Nodal-Line Fermions in TlTaSe2

A topological nodal-line semimetal is a new condensed matter state with one-dimensional bulk nodal lines and two-dimensional drumhead surface bands. Based on first-principles calculations and our effective k . p model, we propose the existence of topological nodal-line fermions in the ternary transition- metal chalcogenide TlTaSe2. The noncentrosymmetric structure and strong spin-orbit coupling give rise to spinful nodal-line bulk states which are protected by a mirror reflection symmetry of this compound. This is remarkably distinguished from other proposed nodal-line semimetals such as Cu3NPb(Zn) in which nodal lines exist only in the limit of vanishing spin-orbit coupling. We show that the drumhead surface states in TlTaSe2, which are associated with the topological nodal lines, exhibit an unconventional chiral spin texture and an exotic Lifshitz transition as a consequence of the linkage among multiple drumhead surface-state pockets.Comment: Related papers at http://physics.princeton.edu/zahidhasangroup/index.htm

Potential of naturally derived alkaloids as multi-targeted therapeutic agents for neurodegenerative diseases

Alkaloids are a class of secondary metabolites that can be derived from plants, fungi and marine sponges. They are widely known as a continuous source of medicine for the management of chronic disease including cancer, diabetes and neurodegenerative diseases. For example, galanthamine and huperzine A are alkaloid derivatives currently being used for the symptomatic management of neurodegenerative disease. The etiology of neurodegenerative diseases is polygenic and multifactorial including but not limited to inflammation, oxidative stress and protein aggregation. Therefore, natural-product-based alkaloids with polypharmacology modulation properties are potentially useful for further drug development or, to a lesser extent, as nutraceuticals to manage neurodegeneration. This review aims to discuss and summarise recent developments in relation to naturally derived alkaloids for neurodegenerative diseases