Appetitive and aversive learning in Spodoptera littoralis larvae

Adult Lepidoptera are capable of associative learning. This helps them to forage flowers or to find suitable oviposition sites. Larval learning has never been seriously considered because they have limited foraging capabilities and usually depend on adults as concerns their food choices. We tested if Spodoptera littoralis larvae can learn to associate an odor with a tastant using a new classical conditioning paradigm. Groups of larvae were exposed to an unconditioned stimulus (US: fructose or quinine mixed with agar) paired with a conditioned stimulus (CS: hexanol, geraniol or pentyl acetate) in a petri dish. Their reaction to CS was subsequently tested in a petri dish at different time intervals after conditioning. Trained larvae showed a significant preference or avoidance to CS when paired with US depending on the reinforcer used. The training was more efficient when larvae were given a choice between an area where CS-US was paired and an area with no CS (or another odor). In these conditions, the memory formed could be recalled at least 24 h after pairing with an aversive stimulus and only 5 min after pairing with an appetitive stimulus. This learning was specific to CS because trained larvae were able to discriminate CS from another odor that was present during the training but unrewarded. These results suggest that Lepidoptera larvae exhibit more behavioral plasticity than previously appreciated.     

Analysis of associative learning in the terrestrial mollusc Limax maximus. II. Appetitive learning

Summary The odor and taste processing systems of the terrestrial mollusc Limax maximus have been shown capable of a number of complex computations. Most of the complex higher-order features of Limax learning have been demonstrated using differential aversive conditioning. The present experiments probe the appetitive learning ability of Limax. In the first experiment a differential appetitive classical conditioning procedure was used. An aversive CS⁺ odor was paired with an attractive taste while a CS^– odor was explicitly unpaired with the attractive taste. This appetitive conditioning procedure dramatically increased the preference for the CS⁺ odor. Further experiments determined the time course of acquisition, the effect of an extinction procedure and long-term retention of the appetitive conditioning. Now that Limax has been shown capable of appetitive conditioning, the neural network simulation of Limax learning, called LIMAX, can be examined for its ability to display appetitive conditioning.Abbreviations AA amyl acetate - CS conditioned stimulus - ISI interstimulus interval - ITI intertrial interval - MCH methylcyclohexanol - US unconditioned stimulus     

Landmark learning and visuo-spatial memories in gerbils

The aim of this study is to understand what a rodent (Meriones unguiculatus) learns about the geometrical relations between a goal and nearby visual landmarks and how it uses this information to reach a goal. Gerbils were trained to find sunflower seeds on the floor of a light-tight, black painted room illuminated by a single light bulb hung from the ceiling. The position of the seed on the floor was specified by an array of one or more landmarks. Once training was complete, we recorded where the gerbils searched when landmarks were present but the seed was absent. In such tests, gerbils were confronted either with the array of landmarks to which they were accustomed or with a transformation of this array. Animals searched in the appropriate spot when trained to find seeds placed in a constant direction and at a constant distance from a single cylindrical landmark. Since gerbils look in one spot and not in a circle centred on the landmark, the direction between landmark and goal must be supplied by cues external to the landmark array. Distance, on the other hand, must be measured with respect to the landmark. Tests in which the size of the landmark was altered from that used in training suggest that distance is not learned solely in terms of the apparent size of the landmark as seen from the goal. Gerbils can still reach a goal defined by an array of landmarks when the room light is extinguished during their approach. This ability implies that they have already planned a trajectory to the goal before the room is darkened. In order to compute such a trajectory, their internal representation of landmarks and goal needs to contain information about the distances and bearings between landmarks and goal. For planning trajectories, each landmark of an array can be used separately from the others. Gerbils trained to a goal specified by an array of several landmarks were tested with one or more of the landmarks removed or with the array expanded. They then searched as though they had computed an independent trajectory for each landmark. For instance, gerbils trained with an array of two landmarks were tested with the distance between two landmarks doubled. The animals then searched for seeds in two positions, which were at the correct distance and in the right direction from each landmark.(ABSTRACT TRUNCATED AT 400 WORDS)     

Optimising synaptic learning rules in linear associative memories

Associative matrix memories with real-valued synapses have been studied in many incarnations. We consider how the signal/noise ratio for associations depends on the form of the learning rule, and we show that a covariance rule is optimal. Two other rules, which have been suggested in the neurobiology literature, are asymptotically optimal in the limit of sparse coding. The results appear to contradict a line of reasoning particularly prevalent in the physics community. It turns out that the apparent conflict is due to the adoption of different underlying models. Ironically, they perform identically at their co-incident optima. We give details of the mathematical results, and discuss some other possible derivations and definitions of the signal/noise ratio.     

Appetitive odor learning does not change olfactory coding in a subpopulation of honeybee antennal lobe neurons

Odors elicit spatio-temporal patterns of activity in the olfactory bulb of vertebrates and the antennal lobe of insects. There have been several reports of changes in these patterns following olfactory learning. These studies pose a conundrum: how can an animal learn to efficiently respond to a particular odor with an adequate response, if its primary representation already changes during this process? In this study, we offer a possible solution for this problem. We measured odor-evoked calcium responses in a subpopulation of uniglomerular AL output neurons in honeybees. We show that their responses to odors are remarkably resistant to plasticity following a variety of appetitive olfactory learning paradigms. There was no significant difference in the changes of odor-evoked activity between single and multiple trial forward or backward conditioning, differential conditioning, or unrewarded successive odor stimulation. In a behavioral learning experiment we show that these neurons are necessary for conditioned odor responses. We conclude that these uniglomerular projection neurons are necessary for reliable odor coding and are not modified by learning in this paradigm. The role that other projection neurons play in olfactory learning remains to be investigated.     

Appetitive Aggression as a Resilience Factor against Trauma Disorders: Appetitive Aggression and PTSD in German World War II Veterans

Background

Repeated exposure to traumatic stressors such as combat results in chronic symptoms of PTSD. However, previous findings suggest that former soldiers who report combat-related aggression to be appetitive are more resilient to develop PTSD. Appetitive Aggression should therefore prevent widespread mental suffering in perpetrators of severe atrocities even after decades.

Methods and Findings

To test the long-term relationship between trauma-related illness and attraction to aggression, we surveyed a sample of 51 German male World-War II veterans (age: M = 86.7, SD = 2.8). War-related appetitive aggression was assessed with the Appetitive Aggression Scale (AAS). Current- and lifetime PTSD symptoms were assessed with the PSS-I. In a linear regression analysis accounting for 31% of the variance we found that veterans that score higher on the AAS show lower PSS-I symptom severity scores across their whole post-war lifetime (β = − .31, p = .014). The effect size and power were sufficient (f ² = 0.51, (1-β) = .99). The same was true for current PTSD (β = − .27, p = .030).

Conclusions

Appetitive Aggression appears to be a resilience factor for negative long-term effects of combat experiences in perpetrators of violence. This result has practical relevance for preventing trauma-related mental suffering in Peace Corps and for designing adequate homecoming reception for veterans.     

Appetitive position discrimination in the T-maze

This protocol details a method to perform appetitively motivated tasks in rodents to test cognitive ability. When testing cognition in animals, the simplest paradigms can potentially yield quick results with minimal investment from the experimenter. Although appetitively motivated tasks are generally learnt more slowly than aversively motivated ones, they may be essential for distinguishing the effects of a treatment on learning from its effects on aversive motivation per se. For example, if a treatment improves learning in both types of paradigm, this is better evidence that it affects cognition rather than sensorimotor processes. Rats and mice easily learn position discriminations in a T-maze, especially if multiple cues, such as different objects and floor textures in the goal arms, are provided. To start, the rodent is placed in the maze and it chooses an arm. This Trial 1, however, is the only one on which this arm will be rewarded. From now on, it must always choose the other arm. The rule is simple: for example, always turn left into the arm with diagonal black stripes on the walls and gravel glued to the floor. High levels of correct responding can be achieved within 20-40 trials. The test may therefore be particularly useful with animals of low cognitive ability, such as transgenic mice derived from some 129 or SJL strains. Once the animals are habituated, each trial should take approximately 1 min. Thus, to test ten animals for 40 trials would take around 7 h.     

Appetitive Associative Olfactory Learning in Drosophila Larvae

In the following we describe the methodological details of appetitive associative olfactory learning in Drosophila larvae. The setup, in combination with genetic interference, provides a handle to analyze the neuronal and molecular fundamentals of specifically associative learning in a simple larval brain.Organisms can use past experience to adjust present behavior. Such acquisition of behavioral potential can be defined as learning, and the physical bases of these potentials as memory traces^1-4. Neuroscientists try to understand how these processes are organized in terms of molecular and neuronal changes in the brain by using a variety of methods in model organisms ranging from insects to vertebrates^5,6. For such endeavors it is helpful to use model systems that are simple and experimentally accessible. The Drosophila larva has turned out to satisfy these demands based on the availability of robust behavioral assays, the existence of a variety of transgenic techniques and the elementary organization of the nervous system comprising only about 10,000 neurons (albeit with some concessions: cognitive limitations, few behavioral options, and richness of experience questionable)^7-10.Drosophila larvae can form associations between odors and appetitive gustatory reinforcement like sugar^11-14. In a standard assay, established in the lab of B. Gerber, animals receive a two-odor reciprocal training: A first group of larvae is exposed to an odor A together with a gustatory reinforcer (sugar reward) and is subsequently exposed to an odor B without reinforcement ⁹. Meanwhile a second group of larvae receives reciprocal training while experiencing odor A without reinforcement and subsequently being exposed to odor B with reinforcement (sugar reward). In the following both groups are tested for their preference between the two odors. Relatively higher preferences for the rewarded odor reflect associative learning - presented as a performance index (PI). The conclusion regarding the associative nature of the performance index is compelling, because apart from the contingency between odors and tastants, other parameters, such as odor and reward exposure, passage of time and handling do not differ between the two groups⁹.     

Appetitive response of the nematodeCaenorhabditis elegans to oxygen

Summary Using a technique of recording the behavior of individual nematodes during exposure to various solutions, it was demonstrated thatC. elegans made more reversal behaviors after transfer to solutions of lower oxygen tension than higher. The response was stronger after the first hour in the apparatus than initially. This change was not dependent on reduced oxygen availability during the initial period. Starvation is the most likely cause of this change. A variety of mutant strains ofC. elegans that are defective in response to most known chemotactic stimuli, including two strains that have been shown to be severely abnormal in the ciliated endings of all sensory neurons of the worm's snout, all responded to changes in oxygen tension. This observation suggests that oxygen is sensed internally rather than by specialized peripheral receptor cells.I thank Deborah Higgins for technical assistance. This work was supported by a grant awarded by the Biomedical Research Support Grant Program of the National Institutes of Health.     

Miasmatic calories and saturating fats: fear of contamination in anorexia

This paper draws on ethnographic material to challenge the taken-for-granted relationship between anorexia and fear of fat. While popular understandings assume anorexia to be an extension of everyday dietary guidelines and a fear of weight gain from foods high in fats and calories, I argue that it is fear of contamination rather than fear of fat per se that is at issue. Through a critique and extension of Mary Douglas' structuralist typology and Julia Kristeva's embodied theory of abjection, I demonstrate that it is the qualities of certain foods, and in particular their amorphous natures, that render them contaminating. Saturating fats and invisible calories are considered dangerous by people with anorexia because they have the ability to move, seep, and infiltrate the body through the interplay of senses. Foods that transgress conceptual and bodily boundaries are thus to be avoided at all costs, for they have the potential to defile and pollute. In light of the low recovery rates for those with anorexia within Australia (and internationally), the findings of this paper have significant implications for the understanding and treatment of this disorder.     

Hyperactivity in anorexia nervosa: warming up not just burning-off calories

Excessive physical activity is a common feature in Anorexia Nervosa (AN) that interferes with the recovery process. Animal models have demonstrated that ambient temperature modulates physical activity in semi-starved animals. The aim of the present study was to assess the effect of ambient temperature on physical activity in AN patients in the acute phase of the illness. Thirty-seven patients with AN wore an accelerometer to measure physical activity within the first week of contacting a specialized eating disorder center. Standardized measures of anxiety, depression and eating disorder psychopathology were assessed. Corresponding daily values for ambient temperature were obtained from local meteorological stations. Ambient temperature was negatively correlated with physical activity (p = −.405) and was the only variable that accounted for a significant portion of the variance in physical activity (p = .034). Consistent with recent research with an analogous animal model of the disorder, our findings suggest that ambient temperature is a critical factor contributing to the expression of excessive physical activity levels in AN. Keeping patients warm may prove to be a beneficial treatment option for this symptom.     

Spatial adaptations for plant foraging: women excel and calories count

We present evidence for an evolved sexually dimorphic adaptation that activates spatial memory and navigation skills in response to fruits, vegetables and other traditionally gatherable sessile food resources. In spite of extensive evidence for a male advantage on a wide variety of navigational tasks, we demonstrate that a simple but ecologically important shift in content can reverse this sex difference. This effect is predicted by and consistent with the theory that a sexual division in ancestral foraging labour selected for gathering-specific spatial mechanisms, some of which are sexually differentiated. The hypothesis that gathering-specific spatial adaptations exist in the human mind is further supported by our finding that spatial memory is preferentially engaged for resources with higher nutritional quality (e.g. caloric density). This result strongly suggests that the underlying mechanisms evolved in part as adaptations for efficient foraging. Together, these results demonstrate that human spatial cognition is content sensitive, domain specific and designed by natural selection to mesh with important regularities of the ancestral world.     

Managing memories in post-war Sarajevo: individuals, bad memories, and new wars

In the wake of the 1992-5 war in Bosnia a number of anthropologists have written about the role of memory in creating and sustaining hostility in the region. One trend focuses on the authenticity and power of personal memories of Second World War violence and on the possibility of transmitting such memories down the generations to the 1990s. Another focuses less on memory as a phenomenon which determines human action than on the 'politics of memory': the political dynamics which play on and channel individuals' memories. In this article I use the example of three Sarajevo Bosniacs whom I have known since the pre-war 1980s in order to propose the merit of a third, additional, focus on the individual as an active manager of his or her own memories. I briefly consider whether work by Maurice Bloch on the nature of semantic and of autobiographic memory supports a strong version of the first interpretative trend, or whether, as I suggest, the conclusions of this work instead leave room for individual memory management and for change down the generations.