Integrating Spatial Working Memory and Remote Memory: Interactions between the Medial Prefrontal Cortex and Hippocampus

In recent years, two separate research streams have focused on information sharing between the medial prefrontal cortex (mPFC) and hippocampus (HC). Research into spatial working memory has shown that successful execution of many types of behaviors requires synchronous activity in the theta range between the mPFC and HC, whereas studies of memory consolidation have shown that shifts in area dependency may be temporally modulated. While the nature of information that is being communicated is still unclear, spatial working memory and remote memory recall is reliant on interactions between these two areas. This review will present recent evidence that shows that these two processes are not as separate as they first appeared. We will also present a novel conceptualization of the nature of the medial prefrontal representation and how this might help explain this area’s role in spatial working memory and remote memory recall

Continuous Theta Rhythm During Spatial Working Memory Task in Rodent Models of Streptozotocin-induced Type 2 Diabetes

Alzheimer’s disease is a neurodegenerative disorder altering memory loss thought to be due to neuropathological symptoms such as the buildup of beta amyloid plaques (Ab) and neurofibrillary tangles (NFT). The etiology of Alzheimer’s is still unknown; however, potential risk factors such as diabetes may lead to its development. The most common form of diabetes is type 2 diabetes known for persistent insulin resistance leading to a state of hyperglycemia. Insulin resistance has been shown to affect cognitive abilities such as learning, memory and also alters synaptic plasticity. Neural connections between the hippocampus (HC) and anterior cingulate cortex (ACC) are known to be very important for learning and memory and are highly plastic, making them an intriguing target that could be altered by hyperglycemia. We hypothesize that hyperglycemic rodents will exhibit spatial memory deficits that may be associated with cognitively linked interactions between the HC and ACC. Minimal doses of streptozotocin (STZ), which is toxic to insulin producing beta cells, were given for 9-10 weeks. Using a spatial working memory task known as delayed alternation we found significant differences between control and experimental rats in working memory accuracy. This task places strong working memory demands on subjects which may be compromised by a hyperglycemic state. We measured EEG recordings from the HC and ACC during task performance and found that hyperglycemic rats had nearly continuous theta rhythm during the 30-minute session. Control rats however, displayed normal transitions between theta and lower frequency delta. Neural connectivity may be altered due to a change in frequency activity between the HC and ACC due to diabetes which is a risk factor in the development of AD impairments. These results show that hyperglycemia leads to changes along the circuit critical for learning and memory

Changes in Hippocampal-Anterior Cingulate Cortex Interactions During Remote Memory Recall

Spatial memory is an important cognitive process that relies on extensive neural networks throughout the brain. The hippocampus (HC) is important for the formation of these memories but over time, in a process referred to as consolidation, recall becomes increasingly reliant on other brain areas. The anterior cingulate cortex (ACC), a region within the medial prefrontal cortex, is important for spatial learning, spatial working memory, and remote memory recall, but the mechanisms underlying recall processes are still unknown. To better understand the role of the ACC and HC during memory recall, we introduced rodents into a series of spatially and texturally unique environments at differing delay periods (day 1 (learning), day 11 (recent), and day 18 (remote)) while simultaneously recording local field potentials (LFPs) from both areas. We found significant increases in theta band coherence between ipsilateral ACC and HC LFPs during remote memory recall but not recent memory recall. In addition to these changes, directional analysis revealed a reversal in signal initiation, such that during the learning and recent recall condition, hippocampal theta oscillations led ACC theta oscillations. However, during the remote recall condition, the direction changed, and ACC theta led hippocampal theta activity. This experiment provides evidence of time-dependent changes in ACC – hippocampal network interactions, and illustrates a possible mechanism that describes how the ACC mediates recall of remote spatial memories

Construction and Assembly of a Hyperdrive Recording Implant

The ability to record neural activity from multiple brain areas is crucial for the understanding of how different areas of the brain function or interact. This poster will cover instructions on how to construct and assemble a hyperdrive recording implant that bilaterally targets the ACC and the hippocampus. Intriguingly, the design of the hyperdrive recording implant is flexible and can be constructed to target other brain areas. The implant consists of 32 twisted bundles of tetrodes with a total of 128 individual recording wires which are controlled by movable ‘drivers’ (Gray et al., 1995; McNaughton et al., 1983). All 128 recording wires are then connected to an electrode interface board that takes information from the brain and transfers it to online available open-source acquisition software platform running. Using this implant with targeted tetrodes, we are able to look at the neuronal waveforms of individual neurons or the population-level responses in specific brain areas

ACC Theta Improves Hippocampal Contextual Processing during Remote Recall

Consolidation studies show that, over time, memory recall becomes independent of the medial temporal lobes. Multiple lines of research show that the medial frontal cortex, including the anterior cingulate cortex (ACC), is involved with contextual information processing and remote recall. We hypothesize that interactions between the ACC and hippocampal area CA1 will change as memories became more remote. Animals are re-exposed to multiple environments at different retention intervals. During remote recall, ACC-CA1 theta coherence increases, with the ACC leading area CA1. ACC theta regulates unit spike timing, gamma oscillations, and ensemble and single-neuron information coding in CA1. Over the course of consolidation, the strength and prevalence of ACC theta modulation grow, leading to richer environmental context representations in CA1. These data are consistent with the transference of contextual memory dependence to the ACC and indicate that remote memories are retrieved via ACC-driven oscillatory coupling with CA1

Diabetes Mellitus Affects Working Memory

Alzheimer’s disease (AD) degrades the brain’s ability to remember, think, and carry out tasks. The exact cause is not known, but several risk factors have been identified, including diabetes mellitus (DM). DM causes elevated blood sugar levels due to reduced insulin production in the pancreas. The linkage between elevated glucose levels and the behavioral impairments are not fully understood, which was the focus of this study. Rats were trained to alternate directions in a maze to receive a reward on consecutive trials. After training, five rats were injected with streptozotocin (STZ), which induces hyperglycemia by injuring pancreatic beta cells. Three control animals received benign vehicle injections. All eight rats then underwent implant surgery and received an implant with 128 recording probes attached to an electronic interface board. The recording electrodes targeted the hippocampus and the anterior cingulate cortex (ACC), which are both associated with learning and memory processes. We found that STZ rats had reduced accuracy after long delay periods compared to the control rats. During task performance, there was a decrease in the power of theta activity and an increase in delta activity moments before starting a new trial. This was the opposite of control animals, who before starting new trials had higher theta power and less delta power as they focused. These findings imply that the STZ rats were impaired on longer delay periods. These findings are like reports from animal models of AD and may help explain why DM is a risk factor for AD

Ecological resilience indicators for salt marsh ecosystems

Salt marshes are coastal ecosystems within the intertidal zone, characterized by hypoxic, saline, soil conditions and low biodiversity. Low diversity arises from frequent disturbance and stressful conditions (i.e., high salinity and hypoxia), where vegetative reproduction and low competition result in mostly monotypic stands, with some differences in plant community influenced by flooding regime (described below). While there are several types of salt marshes in the Northern Gulf of Mexico (NGoM), ranging from low to high salt marshes and salt flats (Tiner, 2013), Spartina alterniflora–dominated salt marshes in the Coastal and Marine Ecological Classification Standard (CMECS) Low and Intermediate Salt Marsh Biotic Group (FGDC, 2012) are the most extensive and are the focus of this project. These salt marshes are classified as “Gulf Coast Cordgrass Salt Marsh” (CEGL004190; USNVC, 2016). Within the NGoM region, some salt marsh areas are dominated by other species such as Spartina patens and Juncus roemerianus, which both occupy higher elevations in high-precipitation zones (e.g., Louisiana, Alabama, Mississippi, and Florida). In lower precipitation regions (southern Texas), hypersaline conditions often develop yielding communities of succulent salt marsh plants (Batis and Salicornia spp.). In climatic zones with warmer winter temperatures, temperate salt marshes naturally transition to mangrove (generally in the southern Gulf of Mexico range) or, in areas with lower precipitation, to salt flats (generally in western part of the study area)

A Comparison of Cervical and Trunk Musculoskeletal Characteristics between Female and Male Army Helicopter Pilots

Introduction: Neck pain (NP) and low back pain (LBP) are prevalent among military helicopter pilots. Although there have been few studies on sex differences in the NP/LBP prevalence in this population, females are shown to be at a greater risk of NP/LBP in civilian studies. This disparity may be due to musculoskeletal characteristics differences that predispose females for NP/LBP. The purpose of this study was to compare cervical and trunk musculoskeletal characteristics between male and female pilots. Methods: A total of 8 female pilots (Age: 27.6 ± 4.2yrs, HT: 166.1 ± 7.7cm, WT: 67.9 ± 10.6kg) were tested, and they were matched (1:1 matching ratio) with male pilots (Age: 27.8 ± 4.2yrs, HT: 175.0 ± 6.8cm, WT: 79.5 ± 5.8kg), based on age (± three years) and flight experience (± two years). Cervical/trunk strength and flexibility were tested using the hand-held/isokinetic dynamometer and inclinometers, respectively. Strength values were normalized to body weight for analyses. Paired t-tests or Wilcoxon Signed Rank tests were used to examine sex differences across all variables (p \u3c 0.05). Results: Female pilots had significantly lower cervical flexion strength, trunk flexion strength, and trunk rotation strength (p \u3c 0.05). For flexibility measures, female pilots had significantly greater cervical rotation flexibility (p \u3c 0.05). No significant differences were observed in the lumbar spine flexibility. Discussion/Conclusion: The current preliminary study found sex differences in cervical and trunk musculoskeletal characteristics in Army helicopter pilots. Continued efforts are warranted to explore sex-specific intervention strategy and its effectiveness in reducing the NP/LBP prevalence among military helicopter pilots

The Hydrogen Epoch of Reionization Array Dish II: Characterization of Spectral Structure with Electromagnetic Simulations and its science Implications

We use time-domain electromagnetic simulations to determine the spectral characteristics of the Hydrogen Epoch of Reionization Arrays (HERA) antenna. These simulations are part of a multi-faceted campaign to determine the effectiveness of the dish's design for obtaining a detection of redshifted 21 cm emission from the epoch of reionization. Our simulations show the existence of reflections between HERA's suspended feed and its parabolic dish reflector that fall below -40 dB at 150 ns and, for reasonable impedance matches, have a negligible impact on HERA's ability to constrain EoR parameters. It follows that despite the reflections they introduce, dishes are effective for increasing the sensitivity of EoR experiments at relatively low cost. We find that electromagnetic resonances in the HERA feed's cylindrical skirt, which is intended to reduce cross coupling and beam ellipticity, introduces significant power at large delays ($-40$ dB at 200 ns) which can lead to some loss of measurable Fourier modes and a modest reduction in sensitivity. Even in the presence of this structure, we find that the spectral response of the antenna is sufficiently smooth for delay filtering to contain foreground emission at line-of-sight wave numbers below $k_\parallel \lesssim 0.2$ $h$Mpc$^{-1}$, in the region where the current PAPER experiment operates. Incorporating these results into a Fisher Matrix analysis, we find that the spectral structure observed in our simulations has only a small effect on the tight constraints HERA can achieve on parameters associated with the astrophysics of reionization.Comment: Accepted to ApJ, 18 pages, 17 Figures. Replacement matches accepted manuscrip

The Hydrogen Epoch of Reionization Array Dish I: Beam Pattern Measurements and Science Implications

The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer aiming to detect the power spectrum of 21 cm fluctuations from neutral hydrogen from the Epoch of Reionization (EOR). Drawing on lessons from the Murchison Widefield Array (MWA) and the Precision Array for Probing the Epoch of Reionization (PAPER), HERA is a hexagonal array of large (14 m diameter) dishes with suspended dipole feeds. Not only does the dish determine overall sensitivity, it affects the observed frequency structure of foregrounds in the interferometer. This is the first of a series of four papers characterizing the frequency and angular response of the dish with simulations and measurements. We focus in this paper on the angular response (i.e., power pattern), which sets the relative weighting between sky regions of high and low delay, and thus, apparent source frequency structure. We measure the angular response at 137 MHz using the ORBCOMM beam mapping system of Neben et al. We measure a collecting area of 93 m^2 in the optimal dish/feed configuration, implying HERA-320 should detect the EOR power spectrum at z~9 with a signal-to-noise ratio of 12.7 using a foreground avoidance approach with a single season of observations, and 74.3 using a foreground subtraction approach. Lastly we study the impact of these beam measurements on the distribution of foregrounds in Fourier space.Comment: 13 pages, 9 figures. Replaced to match accepted ApJ versio