Platform Positions Research Articles

Pretraining or previous non-spatial experience improves spatial learning in the Morris water maze of nucleus basalis lesioned rats

Previous experiments have shown that infusions of ibotenic acid in the nucleus basalis magnocellularis (NBM) induce a strong impairment in spatial navigation for a hidden platform in the Morris water maze. This effect was initially attributed to a cholinergic deficit, but later studies showed that performance level did not correlate with the degree of cholinergic denervation. Therefore, this impairment is due to a combined cholinergic and non-cholinergic deficit. However, it is not clear in which particular processes the NBM is involved. In this study we have evaluated the origin of behavioural impairment in spatial navigation in the water maze after an ibotenic acid-induced lesion of NBM. In the first experiment, Wistar rats were trained preoperatively in an allocentric navigation task. Postoperatively, they were tested in the same task. All lesioned animals showed a performance level similar to controls. Lesions did not impede the acquisition of new positions in the water maze, nor did affect the ability of animals to remember new platform positions after an intertrial interval of 20 s, even if animals had received only allocentric experience with the platform position, or allocentric and path integration information concurrently. Lesions also failed to affect the ability to locate a hidden platform in a new environment. However, hippocampal infusions of scopolamine (5 μg) produced a severe impairment in NBM-damaged animals, without impairing performance of controls. In the second experiment Wistar rats with the same lesion were first trained in a visual-guided task in the water maze, and subsequently evaluated in the spatial task. In both tasks lesioned animals were not different from controls. These results suggest that the NBM played an important role during acquisition phases but not in the execution of spatial navigation. Moreover, the excessive emotional response displayed by lesioned animals is postulated as a relevant cause for the impairment observed in spatial navigation after NBM damage.

Restricted feeding facilitates time–place learning in adult rats

Many species can acquire time-of-day discrimination when tested in food reinforced place learning tasks. It is believed that this type of learning is dependent upon the ability of animals to consult their internal circadian pacemakers entrained by various environmental zeitgebers, such as light–dark cycles and scheduled restricted feeding. In the present study, we examined, (1) whether rats can acquire time-of-day discrimination in an aversively motivated water maze task wherein an escape platform is located in one position in the morning and in another position in the afternoon; (2) whether time-of-day cues provided by the light- and feeding-entrainable pacemakers may have divergent impacts upon the ability of rats to learn this task. Two groups of rats, both maintained on 12-h light:12-h dark cycle, were used; in one group, animals had free access to food, whereas in the other, they were subjected to a restricted feeding protocol (60% of food consumed by rats fed ad libitum, once daily). Despite the heightened difficulty of the task, food-restricted rats were apparently able to acquire associations between two different platform positions and two different times of day, as indicated by the fact that the percentage of discrimination errors in this group declined progressively, as a function of training, and stabilized at the level of 22±9%. In contrast, rats that were fed ad libitum, even after extensive training, failed to perform the task above level of chance. These data indicate that time–place learning is a universal, reward-nonspecific, cognitive phenomenon. They furthermore suggest that the ability of animals to integrate spatial and temporal information can be dependent on the access to timing stimuli provided by the feeding-entrainable circadian system.

Spatial learning, contextual fear conditioning and conditioned emotional response in Fmr1 knockout mice

Fmr1 knockout mice are an animal model for fragile X syndrome, the most common form of heritable mental retardation in humans. Fmr1 knockout mice exhibit macro-orchidism and cognitive and behavioural deficits reminiscent of the human phenotype. In the present study additional behavioural and cognitive testing was performed. Knockouts and control littermates were subjected to a spatial learning test using a plus-shaped water maze. Animals had to learn the position of a hidden escape platform during training trials. The position of this platform was changed during subsequent reversal trials. Previously reported deficits in reversal learning were replicated, but we also observed significant differences during the acquisition trials. A plus-shaped water maze experiment with daily changing platform positions failed to provide clear evidence for a working memory impairment, putatively underlying the spatial learning deficits. Two different test settings were used to examine the reported deficit of Fmr1 knockout mice in fear conditioning. Conditioned fear responses were observed in a contextual fear test, and the ability to acquire an emotional response was tested by means of response suppression in a conditioned emotional response procedure. Neither protocol revealed significant differences between controls and knockouts.

Sequential elections and overlapping terms: voting for US Senate

This paper presents a model in which voters attempt to balance the ideological positions of their Senate representatives. Candidate positions are determined endogenously through a primary system. The median voter theorem is applied in each election to determine winning platforms based on voter preferences which may differ from their individual bliss points. Contrary to the original median voter theorem, the main implications of this model are that: (i) convergence on platform positions is not achieved in the general election, and (ii) extremist candidates defeat moderates in the stable long-run equilibrium.

Polarized platforms and moderate policies with checks and balances

In standard spatial models of elections, parties with policy preferences take divergent positions. Their platform positions are less separated than are the parties’ ideal policies. If policy is the result of an executive–legislative compromise, the policy preferences of the parties can be moderated by voter behavior. Divided government may result. Since parties anticipate the moderated outcomes, they have an added incentive to choose separated platforms. Consequently, divergence in platforms is greater than in the standard model, especially when uncertainty is high and the legislature more powerful than the executive. For some parameters, parties may even ‘posture’ by adopting platforms that are more extreme than their ‘true’ ideal points.

The effect of water maze spatial training on posterior parietal cortex transcallosal evoked field potentials in the rat.

Long-term potentiation (LTP) is the principal model of synaptic plasticity often used to explain the changes that occur in the brain as a result of learning and memory. In this experiment the relationship between rat posterior parietal cortex (PPC) transcallosal evoked field potentials (TCEPs) and spatial training in the water maze was examined to determine if LTP-like changes (i.e. learning-induced LTP) in PPC TCEPs occur as a result of spatial training. Spatial training consisted of 10 trials per day for 10 consecutive days. The location of the hidden platform was changed over the course of spatial training to ensure the rats' acquisition of several different platform positions. TCEPs were taken 1 and 23 h after each training session. Upon completion of all water maze training, the animals were administered LTP-inducing trains to ensure that the recording arrangement and procedure was capable of detecting LTP. The results showed that the rats quickly acquired the water maze task and that the recording arrangement and procedure were capable of detecting LTP, even after the first session of induction. However, despite robust place learning, the TCEPs taken after water maze training did not differ from those taken before water maze training. Although the present results failed to provide any evidence for a role of neocortical LTP in learning and memory, further studies of this nature are required to determine if the present results generalize to different behavioural tasks and/or cortical areas.

Working memory deficits following traumatic brain injury in the rat.

This study was designed to examine working memory following fluid-percussion traumatic brain injury (TBI) using the Morris water maze (MWM). Rats were injured (n = 9) at a moderate level of central fluid percussion injury (2.1 atm) or were prepared for injury but did not receive a fluid pulse (sham injury) (n = 10). On days 11-15 postinjury, working memory was assessed using the MWM. Each animal received 8 pairs of trials per day. For each pair of trials, animals were randomly assigned to one of four possible starting points and one of four possible escape platform positions. On the first trial of each pair, rats were placed in the maze facing the wall and were given 120 sec to locate the hidden escape platform. After remaining on the goal platform for 10 sec, they were placed back into the maze for the second trial of the pair. The platform position and the start position remained unchanged on this trial. After the second trial, the animal was given a 4 min intertrial rest. Between pairs of trials, both the start position and the goal location were changed. Analyses of the latency to reach the goal platform indicated that sham-injured animals performed significantly better on the second trial than on the first trial of each pair. However, injured animals did not significantly differ between first and second trial goal latencies on any day. These results indicate that injured animals have a profound and enduring deficit in spatial working memory function on days 11-15 after TBI.

Texas Woman's University and White House Communications on the Internet

During the course of the 1992 United States Presidential campaign, electronic discussion lists were established on Bitnet which allowed "subscribers" to openly discuss issues relevant to each candidate's campaign. A discussion list was formed for each of the three candidates. In the summer of 1992, the Clinton and Bush campaigns began posting full-text documents (speeches, interviews, platform positions, etc.) to each respective list on Bitnet, making available information that was almost nonexistent in any other format to faculty and students at Texas Woman's University. It was soon discovered that these documents were available elsewhere, but only through the Internet, and they were readily accessible for the taking. Organizations such as the federally sponsored Hermes Project and the National Public Telecmuting Network (NPTN) also provided access to these documents. The reference department at TWU soon took advantage of this information, and with the realization that most of the university community was still alien to electronic file transfer and Bitnet discussion lists, decided to make these documents available in a more traditional manner by retrieving them either through the discussion list or through one if the their organizations providing campaign documents via the Intemet. This article documents the reference department as an instrumental part in using the IInternet in the acquisistion of these campaign documents both before and after the November election for use by faculty and students, as well as members of the city Denton, Texas.

Dynamics of Trunk Performance during One-Handed Lifting

This study investigated the biomechanical effects of using one hand to perform a materials handling task. Subjects were asked to lift a box from a lower to an upper platform using either one or two hands. Three weight levels and four lower platform positions were examined. Subjects wore a back monitor (from which was calculated motion components in the three cardinal planes of the body), stood on a force plate, and were asked to give a rating of perceived exertion for each lift. Results of this study showed that one-handed lifts produced significantly higher ranges of lumbar spine motion in the lateral and transverse planes and greater flexion in the sagittal plane. Back motion risk factors previously found to be associated with high risk of injury jobs all were significantly higher for one-handed lifts. Two-handed lifts, however, produced overall faster motions in the sagittal plane, and equal or larger acceleration and deceleration magnitudes in all planes of motion. Results from the psychophysical measure found no differences in perceived exertion between one- and two-handed lifts. These results suggest that one-handed lifts load the spine more than two-handed lifts due to the added coupling and increase one's risk of suffering a low back disorder. This study also agrees with previous research finding that increased load weight and lifting from asymmetric positions increase risk of low back injury.

Pretraining morphine impairs acquisition and performance in the Morris water maze: Motivation reduction rather than anmesia

Two experiments were designed to assess the contribution of central opioid systems to spatial memory in the rat. In Experiment 1, rats were given morphine (5, 10, or 20 mg/kg), naloxone (2 mg/kg), morphine (20 mg/kg) plus naloxone (2 mg/kg), or saline and were trained to locate either a submerged or a visible platform in the Morris water maze. Pretraining, but not posttraining, morphine dose-dependently impaired acquisition and retention of the submerged platform tasks. Morphine also impaired acquisition of the visible-platform task. Naloxone reversed the morphine deficits but had no effect on place or cue learning when administered alone. In Experiment 2, rats were given morphine (10 mg/kg), naloxone (2 mg/kg), or saline and were required to locate a series of novel platform positions in either warm (38 °C, low incentive) or cold (10 ° C, high incentive) water. Morphine-treated rats showed large deficits in the warm water but minimal deficits in the cold water for both the submerged and the visible platforms, suggesting that morphine impairs place and cue learning by reducing the incentive to escape.

A method for locating targets using range only

Suppose that we have the distances to p + 1 targets obtained from a moving platform at discrete times with the ( p + 1)st target being a reference beacon. Assume that the distances are measured with an additive error which has a zero mean and that the errors are uncorrelated in time and space. Given the knowledge of the error structure, the position of the reference target, and the set of the successive simultaneous ranges, we present a statistical method for accurately determining the positions of the remaining targets in a computationally reasonable manner, assuming that the platform positions satisfy a certain constraint. Alternatively, reversing the roles of targets and observer, the method can be used to track a moving target platform using ranges simultaneously measured from p observers whose fixed positions are known, provided that there is a ( p + 1)st observer at a known position. As long as the target track is sufficiently variable, the discrete-time range data can be used to estimate the position of the p observers and the target track. In practice the method could be used to refine the location estimates of the observers based on successive simultaneous range measurements of the target while tracking the target. If {\sl two} observer positions {sl are known}, {sl no constraint} has to be put on the target track. The technique is analyzed using several artificial data sets for one reference target (or observer). We show that when the error is small we obtain an accurate map of ten fixed targets from 500 platform locations, and the map is also reasonably accurate even when the mean error is 70 percent of the average true distance. We also analyze another model that has 14 targets observed from 1000 locations but where the location of two of these targets are known. In any of the scenerios, as the number of successive range measurements whose errors are uncorrelated grows to infinity, the coordinate estimates of the p target (observer) locations converges in probability to the true coordinates.

A Random Doppler Measurement Technique for the Global Atmospheric Research Program

Abstract A proposed satellite-based environmental measurement system could contribute some Of the important basic variables to the Global Atmospheric Research Program (GARP) initial data set at low cost and within acceptable limits of accuracy. Randomly-timed signals from constant-level balloons, free-drifting buoys, and remote land stations would transmit in situ data to the satellite via low power modulated oscillators; doppler shifts in the signal frequency would allow computation of the platform positions. No satellite interrogation of the environmental platforms would be necessary. The capabilities, function, and comparative advantages of the proposed system are enumerated.