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At least 1,639 records · Page 91Linked to original sources
PubMed2006

Optimal strategy for time-limited sequential search.

An optimal strategy is developed for maximizing the expected benefit in time limited sequential search processes with very low candidate encounter rates. We formulate a model for searches where there are k types of candidates whose benefits and encounter rates are known prior to the start of the search. The optimal strategy consists of determining the specific times during the search at which the acceptable candidate pool should be expanded by including the next lower candidate type in the pool. Results indicate that, in general, candidate types with the higher benefits dominate the optimal strategy.

Animals↗
PubMed2004

Time-dependent changes in alcohol-seeking behaviour during abstinence.

Exposure of alcohol addicts to alcohol-related environmental cues may elicit alcohol-seeking behaviour even after protracted abstinence. The purpose of the present study was to assess time-dependent changes in alcohol-seeking behaviour in rats trained to respond for alcohol. The rats were re-exposed to alcohol-associated stimuli after 1, 28 or 56 days of withdrawal. During the re-exposure session, the rats were first allowed to respond in extinction. Then, reinstatement of alcohol-seeking behaviour was evoked by a complex of discrete alcohol-associated cues (auditory and light cues combined with taste and smell of alcohol). Extinction behaviour depended on abstinence duration with maximal responding after 28-day abstinence. Reinstatement of alcohol-seeking behaviour evoked by the discrete cues was highest after 56-day abstinence. No correlations were found between individual alcohol intakes, extinction behaviour and cue-induced reinstatement. These results suggest that: (i) alcohol-seeking behaviour may become more intense after long-term imposed abstinence; (ii) alcohol self-administration, extinction behaviour, and reinstatement of alcohol-seeking behaviour may be regulated by separate neural mechanisms.

Alcoholism↗
PubMed2005

Pandora neoaphidis transmission and aphid foraging behaviour.

Pandora neoaphidis is an aphid-specific entomopathogen that produces infective conidia. As aphid movement increases, so does the likelihood of contact with conidia. Volatile distress signals released in response to aphid infestation as an indirect defence against herbivory may affect aphid foraging and, therefore, the fungus-aphid interaction. In this study, two different methods were used to investigate the effect of plant volatiles and P. neoaphidis-sporulating cadavers on (1) the colonisation of Vicia faba plants by Acyrthosiphon pisum and (2) P. neoaphidis transmission. This study indicates that A. pisum does not avoid bean plants containing P. neoaphidis and that transmission of conidia occurs during plant colonisation and, to a lesser extent, during in situ feeding. Although significantly more aphids were recovered from damaged plants compared to undamaged plants, the likelihood of infection was not affected by previous infestation by aphids.

Animals↗
PubMed2006

Systematic, standardized and comprehensive neurological phenotyping of inbred mice strains in the German Mouse Clinic.

Neurological and psychiatric disorders are among the most common and most serious health problems in developed countries. Transgenic mouse models mimicking human neurological diseases have provided new insights into development and function of the nervous system. One of the prominent goals of the German National Genome Research Network is the understanding of the in vivo function of single genes and the pathophysiological and clinical consequences of respective mutations. The German Mouse Clinic (GMC) offers a high-throughput primary screen of genetically modified mouse models as well as an in-depth analysis in secondary and tertiary screens covering various fields of mouse physiology. Here we describe the phenotyping methods of the Neurological Screen in the GMC, exemplified in the four inbred mouse lines C57BL/6J, C3HeB/FeJ, BALB/cByJ, and 129S2/SvPas. For our primary screen, we generated "standard operating procedures" that were validated between different laboratories. The phenotyping of inbred strains already showed significant differences in various parameters, thus being a prerequisite for the examination of mutant mouse lines.

Analysis of Variance↗
PubMed2004

How to reliably estimate the tortuosity of an animal's path: straightness, sinuosity, or fractal dimension?

The tortuosity of an animal's path is a key parameter in orientation and searching behaviours. The tortuosity of an oriented path is inversely related to the efficiency of the orientation mechanism involved, the best mechanism being assumed to allow the animal to reach its goal along a straight line movement. The tortuosity of a random search path controls the local searching intensity, allowing the animal to adjust its search effort to the local profitability of the environment. This paper shows that (1) the efficiency of an oriented path can be reliably estimated by a straightness index computed as the ratio between the distance from the starting point to the goal and the path length travelled to reach the goal, but such a simple index, ranging between 0 and 1, cannot be applied to random search paths; (2) the tortuosity of a random search path, ranging between straight line movement and Brownian motion, can be reliably estimated by a sinuosity index which combines the mean cosine of changes of direction with the mean step length; and (3) in the current state of the art, the fractal analysis of animals' paths, which may appear as an alternative and promising way to measure the tortuosity of a random search path as a fractal dimension ranging between 1 (straight line movement) and 2 (Brownian motion), is only liable to generate artifactual results. This paper also provides some help for distinguishing between oriented and random search paths, and depicts a general, comprehensive framework for analysing individual animals' paths in a two-dimensional space.

Animals↗
PubMed2005

Individual discrimination capability and collective decision-making.

Amplification is the main component of many collective phenomena in social and gregarious insects. In a society, individuals face a mixed palette of odours coming from different groups (lines, strains) and individuals present discrimination capabilities. However, often at the collective level, different groups may cooperate and act together. To understand this apparent contradiction, we use a model of food recruitment where each group of foragers have its own blend of pheromone trail that is partly recognized by the others groups. The model shows that a low level of recognition between signals is sufficient to produce a collaborative pattern between groups and that beyond a critical value of recognition, only the aggregation of all the groups around the same food source is observed. The comparison between this model and one describing the site selection by gregarious insects (e.g. cockroach) suggests that such collective response is a generic property of social phenomena governed by amplification processes.

Animals↗
PubMed2006

Food encounter rates of simulated termite tunnels with variable food size/distribution pattern and tunnel branch length.

Subterranean termites excavate tunnels in a search pattern to encounter food in soil. To investigate the effect of food size, food distribution and the branch length of tunnels on food encounter rate we used a lattice gas model to simulate tunnels of the Formosan subterranean termite, Coptotermes formosanus Shiraki. The model made use of minimized local rules derived from empirical data to simulate termite tunnel patterns in featureless soil. Food distributions with three types (uniform, random, and clumped) were defined by using an I-index proposed by Zimmer and Johnson (1985). The food encounter rate was higher in a clumped than in non-clumped (uniform and random) distribution of food particles. When food particle size was varied in random distributions of food particles a maximum encounter rate was found, with particles of larger or smaller size being encountered less frequently. We also discussed the relationship between the branch tunnel length and the tunnel search pattern in minimizing the redundancy of overlapping branches.

Animals↗
PubMed2004

Reinforcement sensitivity theory and personality.

A fully fledged neuroscience of personality is beginning to emerge, shaped and guided in large measure by the seminal work of Jeffrey A. Gray over a period of 40 years. In this Festschrift, I trace the theoretical development of Gray's approach--now known as Reinforcement Sensitivity Theory (RST)--out of the Eysenckian tradition to its most recent articulation. Experimental attempts to test RST are reviewed and the theoretical problems raised by this literature discussed. Also presented are data relating to a recent clarification of RST, viz. the joint subsystems hypothesis, which postulates a fundamental interdependence of appetitive and aversive systems in the typical human laboratory. The value of Gray's general approach to building behavioural theories on the bases of both the conceptual nervous system and the real nervous system is validated in personality, which has long been thought a philosophical mystery rather than a standard problem to be tackled by scientific method.

Animals↗
PubMed2007

Appetitive conditioning: neural bases and implications for psychopathology.

Appetitive conditioning is the process through which new rewards are learned and acquire their motivational salience. Although it has the same evolutionary survival significance as aversive conditioning, appetitive conditioning has rarely been studied in humans. This gap may be explained by the difficulty to find in humans suitable appetitive stimuli that can elicit physiological responses similar to those elicited by aversive stimuli. To help remedy this gap, we review the literature on conditioning, with emphasis on appetitive conditioning. This review comprises three parts. First, we examine the different forms of conditioning. Second, we review the neural basis of appetitive conditioning, particularly from a functional neuroimaging perspective. And third, we demonstrate how perturbations in processes involved in appetitive conditioning can contribute to implicated psychopathologies and suggest neurobiological models underlying these pathologies. The ultimate goal of this review is to stimulate new avenues of research that have direct links to molecular biology, and thus could prove to be invaluable to progress in the understanding and treatment of psychiatric disabilities.

Animals↗
PubMedDate not supplied

A model of active visual search with object-based attention guiding scan paths.

When a monkey searches for a colour and orientation feature conjunction target, the scan path is guided to target coloured locations in preference to locations containing the target orientation [Vision Res. 38 (1998b) 1805]. An active vision model, using biased competition, is able to replicate this behaviour. As object-based attention develops in extrastriate cortex, featural information is passed to posterior parietal cortex (LIP), enabling it to represent behaviourally relevant locations [J. Neurophysiol. 76 (1996) 2841] and guide the scan path. Attention evolves from an early spatial effect to being object-based later in the response of the model neurons, as has been observed in monkey single cell recordings. This is the first model to reproduce these effects with temporal precision and is reported here at the systems level allowing the replication of psychophysical scan paths.

Animals↗
PubMed2004

Ethanol impairs memory of a simple discrimination in adolescent rats at doses that leave adult memory unaffected.

Adolescent rats are less sensitive than adults to the hypothermic, anxiolytic, motor impairing, hypnotic, and lethal effects of ethanol. In vitro experiments nevertheless suggest that hippocampal neural activity is more affected by ethanol in preweanling or adolescent rats than in adults. These data are complemented by in vivo results showing that pretraining ethanol impairs learning in adolescent rats at doses that do not affect adult learning. In order to determine if posttraining ethanol affects memory differently in adolescents than in adults, Sprague-Dawley albino rats of both ages were trained in an appetitively motivated odor discrimination in which they were required to dig in scented sand for sweetened cereal reward. Immediately after training subjects received intraperitoneal injections of 0, 0.5, or 1g/kg ethanol (12.6%). At test, 48h later, subjects were presented with unbaited discriminanda and the time (s) spent digging in the S+ and S- was measured. Adolescents, but not adults, showed impaired discrimination performance if training was followed by ethanol. A subsequent experiment discounted the possibility that impaired adolescent performance was due to ethanol-induced conditioned taste or odor aversions. It thus appears that relative to adults, memory in adolescent rats is more strongly affected by ethanol in a test of appetitive conditioning that excludes ethanol's effects on sensory and motivational influences during the learning experience.

Aging↗
PubMed2005

The sectored foraging field: a novel design to quantify spatial strategies, learning, memory, and emotion.

Although Norway rats are naturally gregarious, males typically live alone at some point during adulthood. Different social ecologies often require different learning strategies and also modulate response to stressors and gonadal development. To measure effects of the social environment on the interaction between cognition and emotion during aging, we focused on a natural learning context and devised the sectored foraging field, a progressively difficult spatial navigation task. Here, we describe how this apparatus and protocol permits multiple learning strategies in a minimally stressful environment, enabling finely graded analyses of cognition and emotionality. Male Sprague-Dawley rats living alone throughout adulthood adopted a sex-typic discernible spatial strategy. In contrast, males housed in group contexts utilized an algorithmic kinesthetic strategy, repeating the same motor action until they found food. Removal of food and distal, but not local cues, elicited anxious alertness, particularly in group-housed males. Cognitive performance of group-housed rats subsequent to food and cue removal was significantly impaired, yet enhanced in isolates.

Animals↗
PubMed2005

Generalization in place learning across geometrically different environments is impaired by hippocampal lesions in rats.

A recent study (Tommasi & Thinus-Blanc, 2004) found that when rats trained to search for food hidden in the center of a square-shaped enclosure were tested in the absence of food, they searched precisely in the center of the enclosure. Transfer tests carried out in enclosures differing in shape or size (rectangular-, large square-, and equilateral triangle-shaped) showed that rats searched in the geometric center of the novel environments. In the present work, half of those rats were lesioned bilaterally to the hippocampus and were then re-trained and re-tested in the same task, to be compared to sham rats that received the same retraining/re-test protocol. Results show that lesioned rats, although unimpaired in relearning to localize the center of the square-shaped enclosure, performed considerably worse than sham rats in the transfer tests in the enclosures differing in shape, suggesting a relevant role of the hippocampus in geometry-driven place generalization.

Animals↗
PubMed2006

Post-training amphetamine administration enhances memory consolidation in appetitive Pavlovian conditioning: Implications for drug addiction.

It has been suggested that some of the addictive potential of psychostimulant drugs of abuse such as amphetamine may result from their ability to enhance memory for drug-related experiences through actions on memory consolidation. This experiment examined whether amphetamine can specifically enhance consolidation of memory for a Pavlovian association between a neutral conditioned stimulus (CS-a light) and a rewarding unconditioned stimulus (US-food), as Pavlovian conditioning of this sort plays a major role in drug addiction. Male Long-Evans rats were given six training sessions consisting of 8 CS presentations followed by delivery of the food into a recessed food cup. After the 1st, 3rd, and 5th session, rats received subcutaneous injections of amphetamine (1.0 or 2.0 mg/kg) or saline vehicle immediately following training. Conditioned responding was assessed using the percentage of time rats spent in the food cup during the CS relative to a pre-CS baseline period. Both amphetamine-treated groups showed significantly more selective conditioned responding than saline controls. In a control experiment, there were no differences among groups given saline, 1.0 or 2.0 mg/kg amphetamine 2 h post-training, suggesting that immediate post-training amphetamine enhanced performance specifically through actions on memory consolidation rather than through non-mnemonic processes. This procedure modeled Pavlovian learning involved in drug addiction, in which the emotional valence of a drug reward is transferred to neutral drug-predictive stimuli such as drug paraphernalia. These data suggest that amphetamine may contribute to its addictive potential through actions specifically on memory consolidation.

Amphetamine↗
PubMedDate not supplied

Toluene alters appetite, NPY, and galanin immunostaining in the rat hypothalamus.

Toluene is a neurotoxic organic solvent widely used in industry and extensively inhaled by solvent abusers. Toluene, diluted 1:1 in olive oil, was administered intraperitoneally at a dose of 1.3 ml/kg/day for 4 days. Controls received the vehicle in the same dose and duration. Food intake and body weight were measured daily. A regional hypothalamic NPY and galanin immunocytochemical study was also performed. Acute toluene administration in rats generated a reduction in food intake and body weight gain. A significant decrease in NPY immunostaining in the paraventricular nucleus and an increase in arcuate nucleus without changes in other hypothalamic regions were observed. Also, acute toluene administration increased galanin immunostaining in paraventricular and arcuate nuclei. These results suggest that the hypothalamic NPY arcuate-paraventricular projection is involved in the anorectic effect of acute high-dose toluene administration. Changes in regional hypothalamic galanin expression could represent a compensatory mechanism against toluene-induced anorexia.

Animals↗
PubMed2004

Effects of chronic ICV leptin infusion on motor-activating effects of D-amphetamine in food-restricted and ad libitum fed rats.

Recently, attention has turned to the possibility that endocrine adiposity hormones, such as leptin, may regulate appetitively motivated behavior by modulating brain dopamine function. By extension, it has been hypothesized that the increased behavioral sensitivity of food-restricted, underweight rats to psychostimulant challenge may be triggered by the accompanying hypoleptinemia. The purpose of the present study was to determine whether two weeks of continuous intracerebroventricular (ICV) infusion of leptin alters the motor-activating effect of D-amphetamine (0.75 mg/kg, IP) in food-restricted rats. Lateral ventricular infusion of leptin, using a regimen that decreases food intake and body weight in ad libitum fed rats (12 microg/day), had no effect on the locomotor response to D-amphetamine in food-restricted rats that were maintained at 80% of prerestriction body weight. This result may indicate that hypoleptinemia is not involved in the induction/maintenance of neuroadaptations that mediate enhanced behavioral sensitivity to psychostimulant challenge. Interestingly, ad libitum fed rats treated with leptin displayed an increased locomotor response to D-amphetamine that was most prominent 3-5 days after termination of the infusion. Body weights and D-amphetamine sensitivity of these subjects returned to control values by 8-10 days postinfusion. The enhanced behavioral sensitivity to D-amphetamine in leptin-treated ad libitum fed rats may be a by-product of adipose depletion and, if so, would further support involvement of a peripheral signal other than hypoleptinemia in the modulation of central sensitivity to psychostimulant challenge.

Animals↗