0237 Effect of Chronic Intermittent Hypoxia on Spatial Performance in Rats

Introduction Cognitive and spatial dysfunction is common among patients with obstructive sleep apnea (OSA). The cause of these abnormalities may be related to the effects of hypoxic damage in the brain during sleep. Here we report a rodent model for chronic intermittent hypoxia (CIH) that examines spatial performance tasks via a Barnes Maze paradigm. We hypothesized that increased severity of CIH yields decreased cognitive and spatial performance. Methods Three groups of rats were subject to varying levels of hypoxia conditions: sham (21% oxygen; n = 19), moderate (11% oxygen; n = 14), and severe (6% oxygen; n = 21). To deliver hypoxia, rats were exposed to three-minute cycles of oxygen between 21% and condition-specific nadir oxygen for 12 hours daily (during sleep) in specialized chambers. Barnes maze testing was performed at 0, 1, 2, and 3 months. Rats were placed on a circular platform with 19 shallow holes and one deeper target hole to escape the noxious sound. Each month, rats had 3 minutes to find the target hole in four daily trials over four consecutive days. Average maze completion time on day 4 was recorded. Results Rats from the three hypoxia groups did not differ significantly in mean maze completion time at baseline (0 months). Throughout the three months of exposure to hypoxic conditions, maze completion time on day 4 did not differ significantly from baseline for sham rats. However, by month 3, rats exposed to severe hypoxic conditions had a significantly larger percent increase from baseline compared to sham rats (p = 0.0358). Conclusion Our findings indicate that rats undergoing intermittent hypoxia perform worse than normoxic rats in spatial performance tasks. These data suggest there is a relationship between CIH and cognitive/spatial impairment. Support Funded by NIH P01 HL094307

Scheduling Concurrent Visual Feedback in Learning a Continuous Balance Task

This investigation held concurrent visual feedback frequency at 50% in the acquisition phase and manipulated three different feedback schedules while comparing those to a 0% feedback frequency. In an assessment of dynamic postural stability, young, healthy adults performed 20 acquisition trials and four retention trials 48-hr later on a circular platform that moved in the anterior/posterior and medial/lateral axes simultaneously. Three concurrent feedback schedules were manipulated: a fade schedule consisting of high relative frequency of concurrent feedback early in the acquisition phase which was systematically reduced throughout acquisition (e.g., 100%, 75%, 50%, 25%, 0%), a constant schedule consisting of a uniform scheduling of concurrent feedback on every other acquisition trial, and a reverse fade group consisting of a schedule exactly opposite to that of the fade group. A no concurrent feedback group was also utilized to determine if feedback was necessary to learn the balance task. Acquisition and retention results revealed the concurrent groups performed with significantly greater accuracy and stability than the no concurrent feedback group. There were no significant differences between the three concurrent feedback schedules. Results indicate that manipulating concurrent feedback scheduling did not produce similar results to those investigations manipulating knowledge of results scheduling.

Robust trajectory tracking control of omni-mobile robot with slipping of the wheels

In this paper we consider the problem of constructing a robust controller to track the trajectory of a mobile robot with three omni-wheels moving on a horizontal surface. A dynamic model of the robot has been constructed such that the center of mass of the circular platform is offset from its geometric center and the wheel slippage occurs during braking. The motion control of the wheeled robot is carried out by using three independent DC motors. The torques developed by the engines are linear with respect to voltage supplied to the engine and to angular velocity of the rotor. Basing on the Lyapunov function method we construct a bounded controller without velocity measurement that solves the robust trajectory tracking problem. This means that for all initial deviations the robot's trajectory falls into a given neighborhood of the tracked trajectory after some time and remains there forever. Theorem on an ultimate boundedness of a closed system is proved. The results of numerical simulation are presented confirming the effectiveness of the proposed controller.

An Older Adult Study of Concurrent Visual Feedback in Learning Continuous Balance

This investigation manipulated concurrent visual feedback for older adults learning to perform a continuous balance task. We randomly assigned 21 older adults to one of three knowledge of results (KR) groups with varying concurrent but always 100% terminal feedback percentages during acquisition: 100% Concurrent and Terminal (100% C&T), 50% Concurrent and 100% Terminal (50% C & 100% T), and 0% Concurrent and 100% Terminal (0% C & 100% T). The continuous balance task involved learning to maintain balance on a circular platform that moved simultaneously on both anterior/posterior and medial/lateral axes. We tested participants before acquisition phase learning and two days afterwards (retention test). At retention testing, participants in the 50% C & 100% T and those in the 0% C & 100% T conditions demonstrated significantly greater accuracy and stability than did participants in the 100% C&T condition. These findings extend previous research with young adults in supporting the guidance theory that too frequent a provision of concurrent knowledge of results negatively affects learning.

Laminar organization of encoding and memory reactivation in the parietal cortex

Egocentric neural coding has been observed in parietal cortex (PC), but its topographical and laminar organization is not well characterized. We used multi-site recording to look for evidence of local clustering and laminar consistency of linear and angular velocity encoding in multi-neuronal spiking activity (MUA) and in the high-frequency (300-900 Hz) component of the local field potential (HF-LFP), believed to reflect local spiking activity. Rats were trained to run many trials on a large circular platform, either to LED-cued goal locations or as a spatial sequence from memory. Tuning to specific self-motion states was observed consistently, and exhibited distinct cortical depth-invariant coding properties. These patterns of collective local and laminar activation during behavior were reactivated in compressed form during post-experience sleep, and temporally coupled to hippocampal sharp wave ripples. Thus, PC neuron motion encoding is consistent across cortical laminae, and this consistency is maintained during memory reactivation.

A New Ballasted Floating Support for Offshore Wind Turbine

In the framework of the developments of renewable marine energy and especially offshore wind energy, different design options of floating support have already been presented in the community such as barge-type, spar-type or semi-submersible-type floating structures. In the present paper, a study conducted by IFPEN is presented in order to design of a new floating platform concept dedicated to a multi-megawatt wind turbine. The design of the concept consists in a circular platform ballasted with water and concrete, anchored to the sea bed through a spread mooring system and designed to accommodate a multi-megawatt (in the range of 5 to 8 MW) offshore wind turbine. The paper focuses on the methodology used in the conceptual and preliminary design phases and then on the major results obtained on the performance of the concept for a wide range of design load cases. The results, at current level, show that the concept is viable and interesting, and that the design can be improved further while requiring some additional validation.