Memory Retention Capability Research Articles

Abstract 22: Evaluation of the effects of CD8 knock-out on cognitive decline in the TAC-induced hypertension mouse model

Hypertension is one of the main risk factors for cognitive impairment and dementia. We and others demonstrated the role of immunoinflammatory challenges in the establishment of cerebral injury following hypertension, highlighting a major role of inflammatory cytokines as interferon-gamma (IFN-γ) and finding increased parenchymal infiltration of CD8+ T cells. To establish the mechanistic role of these cells in cognitive impairment we subjected mice lacking CD8 cells (CD8 KO) and matched controls to aortic coarctation (TAC) and performed advanced neuroimaging analyses with a dedicated 7T small animal MRI, evaluating perfusion, brain volumes, and white matter microstructural integrity. Cognitive performance was evaluated at 4 weeks using the Morris Water Maze (MWM) test. Brain perfusion analyses shown protection from cerebral hypoperfusion in TAC CD8 KO mice compared to TAC WT mice (TAC WT vs TAC KO: 108 vs 148 ml/100g/min, p=0.0298) (Figure A). CD8 KO show preserved microstructural structure at DTI MRI, a typical trait of cerebral injury in clinical and experimental hypertension (Fimbria Fractional Anisotropy, TAC WT vs TAC KO: 0.45 vs 0.54, p=0.0210) , and show no a preserved cognition at MWM (Figure B), with a preserved learning curve at acquisition trial and a preserved memory retention capability evidenced at the probe trial (TAC WT vs TAC KO: 16,4 vs 32.2 seconds spent in platform quadrant, p=0.0014). The rescue from cerebral injury evidenced at MRI and the absence of cognitive impairment in CD8 KO mice demonstrate the pivotal role of CD8+ lymphocytes in the pathogenesis of hypertension-induced cognitive impairment.

Aggregation‐induced suppression of quantum tunneling by manipulating intermolecular arrangements of magnetic dipoles

AbstractThe relaxation time under zero field reflects the memory retention capabilities of single‐molecule magnets (SMMs) when used as storage devices. Intermolecular magnetic dipole interaction is ubiquitous in aggregates of magnetic molecules and can greatly influence relaxation times. However, such interaction is often considered harmful and challenging to manipulate in molecular solids, especially for high‐performance lanthanide single‐ion magnets (SIMs). By an elaborately designed combination of ion pairing and hydrogen bonding, we have synthesized two pseudo‐D5h SIMs with supramolecular arrangements of magnetic dipoles in staggered and side‐by‐side patterns, the latter of which exhibits a 104‐fold slower zero‐field relaxation time at 2 K. Intriguingly, the side‐by‐side complex exhibits a significantly accelerated magnetic relaxation upon diamagnetic dilution, contrary to the general trend observed in the staggered complex. This strongly reveals the presence of aggregation‐induced suppression of quantum tunneling in a side‐by‐side arrangement, which has not been observed in mononuclear SMMs. By leveraging ion‐pairing aggregation and converting to a side‐by‐side pattern, this study successfully demonstrates an approach to transform a harmful intermolecular dipole interaction into a beneficial one, achieving a τQTM of 980 s ranking among the best‐performance SMMs.

Tuning Ambipolarity of the Conjugated Polymer Channel Layers of Floating-Gate Free Transistors: From Volatile Memories to Artificial Synapses.

Three-terminal synaptic transistor has drawn significant research interests for neuromorphic computation due to its advantage of facile device integrability. Lately, bulk-heterojunction-based synaptic transistors with bipolar modulation areproposed to exempt the use of an additional floating gate. However, the actual correlation between the channel's ambipolarity, memory characteristic, and synaptic behavior for a floating-gate free transistor has not been investigated yet. Herein, by studying five diketopyrrolopyrrole-benzotriazole dual-acceptor random conjugated polymers, a clear correlation among the hole/electron ratio, the memory retention characteristic, and the synaptic behavior for the polymer channel layer in a floating-gate free transistor is described. It reveals that the polymers with balanced ambipolarity possess better charge trapping capabilities and larger memory windows; however, the high ambipolarity results in higher volatility of the memory characteristics, namely poor memory retention capability. In contrast, the polymer with a reduced ambipolarity possesses an enhanced memory retention capability despite showing a reduced memory window. It isfurther manifested that this enhanced charge retention capability enables the device to present artificial synaptic characteristics. Theresults highlight the importance of the channel's ambipolarity of floating-gate free transistors on the resultant volatile memory characteristics and synaptic behaviors.

Learning deficits occurs prior to memory retrieval impairment in female Senescence Accelerated Mouse (SAMP8)

AbstractBackgroundThe most regularly used mouse models of Alzheimer's disease in drug development include APP/PS1, 3xTg, and 5xFAD mice. This is a limitation as all these mice represent familial AD. Given sporadic AD accounts for the majority of the AD cases in human, there is an unmet need to validate potential rodent models to better represent sporadic AD. SAMP8 is a naturally‐occurring mouse line that displays many characteristics identified in Alzheimer’s disease (AD) patients, such as learning and memory deficits, and accumulation of beta‐amyloid. In people with preclinical AD, deficits in learning manifest faster than decline in memory retrieval. It is unclear if SAMP8 mice also exhibit this feature, and therefore the current study aims to determine if this feature can be observed in SAMP8, to support the use of SAMP8 as a mouse model of sporadic AD for drug development.MethodThe cognitive function of SAMP8 mice and their age‐matched non‐AD control SAMR1 mice (at various ages) were assessed using Y maze spatial memory test, with 3‐10 min training duration and 1.5‐3 h interval between training and testing session.ResultAt 3‐4 months old, SAMP8 but not SAMR1 failed to differentiate the novel arm from familiar arm in a standard Y maze test (3 min training, 3 h interval). When training time was increased to 10 min, SAMP8 passed the test, while increased training time did not affect the performance of SAMR1 mice. These data indicated that longer training time is required by SAMP8 than SAMR1 to achieve the expected performance, suggesting the presence of learning deficits in SAMP8. Interestingly, at 6‐7 months old, though both SAMP8 and SAMR1 received 10‐min training, only SAMR1 passed the test. The performance of SAMP8 mice was successfully improved by shortening the interval between training and testing (from 3 h to 1.5 hr). These data indicate a deteriorated memory retention capability and a possible impairment in memory retrieval in SAMP8.ConclusionOverall, this study has provided supportive evidence that learning deficits occurs prior to memory retrieval impairment in SAMP8, and the use of SAMP8 as mouse model for AD.

Performance comparison of SRAM cells in 45NM technology in the presence of a memory cell control circuit

Lowering power consumption and increasing the noise margin have become the two most important aspects to be considered in SRAM design. Additionally, a stable operation with good memory retention capability has gained greater importance in obtaining good yield at low-voltage and low-power SRAM designs, due to the fact that parameter variations play a major role in scaled technologies. In this paper, the 6T SRAM, 7T low power SRAM and 7T multi threshold low power SRAM designs are designed, to incorporate power gating technique. The architecture of each of the SRAM designs and their working are analyzed thoroughly. The outputs of the read, write and hold operations with transient response are observed and the power dissipation and static noise margin (SNM) of the each of the SRAM cells is calculated and compared. The paper also presents new power reduction solution through the cell control circuit which reduces the unwanted and spurious switching activities during read and writes operations. The paper demonstrates the reduction of the power con- sumption through the use of cell control circuit.

Something worth remembering: visual discrimination in sharks.

This study investigated memory retention capabilities of juvenile gray bamboo sharks (Chiloscyllium griseum) using two-alternative forced-choice experiments. The sharks had previously been trained in a range of visual discrimination tasks, such as distinguishing between squares, triangles and lines, and their corresponding optical illusions (i.e., the Kanizsa figures or Müller-Lyer illusions), and in the present study, we tested them for memory retention. Despite the absence of reinforcement, sharks remembered the learned information for a period of up to 50weeks, after which testing was terminated. In fish, as in other vertebrates, memory windows vary in duration depending on species and task; while it may seem beneficial to retain some information for a long time or even indefinitely, other information may be forgotten more easily to retain flexibility and save energy. The results of this study indicate that sharks are capable of long-term memory within the framework of selected cognitive skills. These could aid sharks in activities such as food retrieval, predator avoidance, mate choice or habitat selection and therefore be worth being remembered for extended periods of time. As in other cognitive tasks, intraspecific differences reflected the behavioral breadth of the species.

Disordered self assembled monolayer dielectric induced hysteresis in organic field effect transistors.

A memory device using an organic field effect transistor (OFET) with copper phthalocyanine (CuPc) as active material was fabricated and studied. For this purpose, SiO2 dielectric surface was modified with a disordered self assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) molecule which was found to induce large disorder in CuPc film thereby generating more traps for charge carriers. Drain current-drain voltage characteristics at zero gate voltage exhibited large hysteresis which was not observed in OFET devices with ordered OTS monolayer modified and unmodified SiO2 dielectrics. The extent of hysteresis and drain current on/off ratio, reading voltage etc. were found to be dependent on the sweep rate/step voltage employed during scanning. Highest hysteresis with on/off ratio of about 240 was obtained for an optimum step voltage of 2 V while it decreased with further reduction in the same. This was attributed to the longer scanning time leading to release of trapped carriers during forward scan itself. The OFET device was found to exhibit excellent memory retention capability where OFF and ON current measured for about 2 hours after stressing the device at write and erase voltages showed good retention of on/off ratio.

Spatial learning and memory retention in the grey bamboo shark (Chiloscyllium griseum)

Like other vertebrates, fish can learn to solve a wide variety of tasks; however, many of their cognitive abilities, particularly in cartilaginous fishes, still remain unknown. This study investigated memory retention capabilities of spatial learning tasks in the grey bamboo shark (Chiloscyllium griseum, n=8) after behavioural training in a two-choice experiment (T-maze). Sharks learned to obtain food at a goal location, either by performing a specific turn response or by using a variety of external landmarks for guidance. Following successful training, sharks were subjected to several training breaks ranging from one to six weeks, after which they were tested again for memory retention capabilities. Sharks successfully mastered the spatial tasks after 5–21 sessions and retained this knowledge in the absence of reinforcement for a period of up to six weeks. This is the first study to show that sharks, like stingrays and other vertebrates, can solve spatial tasks and retain spatial knowledge for an extended period of time, possibly aiding them in activities such as food retrieval, predator avoidance, mate choice and habitat selection.

Microgeographical variability in long-term memory formation in the pond snail, Lymnaea stagnalis

The ability to learn and form long-term memory (LTM) can enhance an animal’s fitness, for example by allowing it to remember predators, food sources or conspecific interactions. Here we used the great pond snail, Lymnaea stagnalis, to assess whether variability among natural populations in memory-forming capabilities occurs on a microgeographical scale. We used four populations from two different habitat types separated by 1–20 km: two from large, permanent canals and two from small, fluctuating drainage ditches. Of the four populations tested, only one, from a small drainage ditch, formed LTM lasting 24 h after a 0.5 h operant training session to reduce aerial respiration in hypoxic conditions when trained in pond water alone. Each of the four populations demonstrated the same memory retention capability over 2 consecutive years, indicating temporal stability within each population tested. Despite this lack of a consistent ability for LTM formation among populations in pond water, all populations tested demonstrated LTM formation in the presence of predator kairomones, from both tench, Tinca tinca, a predatory fish present at the large canal sites, and crayfish, Pacifastacus leniusculus, known to extend memory in a Dutch L. stagnalis population. Therefore, while we found differences between populations in LTM retention after training in pond water, the response to predator kairomones during training, an ecologically relevant stressor, appears highly conserved in this species, enabling all populations to form LTM.

Radiation Induced Charge Loss Mechanisms Across the Dielectrics of Floating Gate Flash Memories

One of the key factors permitting the extraordinary success of floating gate (FG) nonvolatile memories relies on the excellent insulating properties of the dielectric layers surrounding the FG itself. Among other threats, ionizing radiation may effectively affect such insulating characteristics, leading to a degradation of the FG stored charge. Radiation effects have been traditionally studied for niche applications such as the high energy physics or the satellite industry. However, modern semiconductor technologies are becoming more and more sensitive to the deposition of small amounts of charge, such as those generated by the byproducts of atmospheric neutrons, and FG memories are in fact aggressively scaled following Moore's law predictions. Loss of information may derive from two broad categories of phenomena, Total Ionizing Dose and Single Event Effect, whose actions on the FG dielectrics are reviewed in this contribution from the viewpoints of the prompt induced damage and long-term degradation effects, affecting the memory retention capabilities.

On-line learning without forgetting for language acquisition

In this paper, a new method for on-linetraining that overcomes interference in neural networks is presented. The language acquisition problem is modeled as a system of linear equations as first given by Gorin etal. [A. Gorin etal., ‘‘Adaptive Acquisition of Language,’’ in NeuralNetworks, TheoryandApplications, edited by R. J. Mammone and Y. Y. Zeevi (Academic, New York), p. 125]. The new method encodes data patterns or words that have been learned previously as a set of convex constraints. On-line training is then implemented using the row action projection (RAP) algorithm to readjust the weights subject to these convex constraints. The RAP algorithm asymptotically converges to the pseudoinverse solution in the case of simple linear constraints. The computational complexity of conventional methods of calculating the pseudoinverse make them unsuitable for on-line applications. The previously learned patterns are viewed as long-term memory while the on-line data is considered to reside in short-term memory. Memory retention is obtained in the new approach by storing the patterns that are close to the feature space boundaries in long-term memory. These stored patterns are then used as convex constraints for any subsequent on-line learning. In contrast to previous block learning strategies, the new approach learns the meaning of words sequentially. This enables the on-line training of a connectionist network. Computer simulations are presented that demonstrate the memory retention capabilities of the new on-line training algorithm.

Memory Performance of MOS Transistors with SiO2 Films Prepared by SiH4–H2O System

Memory characteristics of MOS transistors and MOS diodes with SiO2 films deposited by using the SiH4–H2O system were evaluated by measuring the I–V characteristics, the C–V hysteresis, the shift in threshold voltage (ΔVT) and memory retention capability. These characteristics were compared with those of MNOS transistors. The results indicate that MOIOIIOIIIS structure (OI: SiO2 film deposited using the SiH4–NO2 system, OII: SiO2 film deposited using the SiH4–H2O system, OIII: thermally grown SiO2 film) has a good retention capability, and MOIIOIIIS transistor is more likely to show the shift characteristics of ion drift type than MNOIIIS transistor of the same dimensions. From the various experimental results, it is concluded that memory performance of MOIIOIIIS transistor exhibiting the shift characteristics of ion drift type is better than that of MNOIIIS transistor.