Short- and long-term habituation of photonegative and exploratory responses in the flatworm planaria (Dugesia)

Behavioural ecology meets oncology: quantifying the recovery of animal behaviour to a transient exposure to a cancer risk factor

Wildlife is increasingly exposed to sublethal transient cancer risk factors, including mutagenic substances, which activates their anti-cancer defences, promotes tumourigenesis, and may negatively impact populations. Little is known about how exposure to cancer risk factors impacts the behaviour of wildlife. Here, we investigated the effects of a sublethal, short-term exposure to a carcinogen at environmentally relevant concentrations on the activity patterns of wild Girardia tigrina planaria during a two-phase experiment, consisting of a 7-day exposure to cadmium period followed by a 7-day recovery period. To comprehensively explore the effects of the exposure on activity patterns, we employed the double hierarchical generalized linear model framework which explicitly models residual intraindividual variability in addition to the mean and variance of the population. We found that exposed planaria were less active compared to unexposed individuals and were able to recover to pre-exposure activity levels albeit with a reduced variance in activity at the start of the recovery phase. Planaria showing high activity levels were less predictable with larger daily activity variations and higher residual variance. Thus, the shift in behavioural variability induced by an exposure to a cancer risk factor can be quantified using advanced tools from the field of behavioural ecology. This is required to understand how tumourous processes affect the ecology of species.

A Navigation Algorithm to Enable Sustainable Control of Insect-Computer Hybrid Robot with Stimulus Signal Regulator and Habituation-Breaking Function

The insect-computer hybrid soft robots are receiving increasing attention due to their excellent motor capabilities, small size, and low power consumption. However, the effective control of insects is limited to minutes since the response from insects is reduced as the number of stimulus signal increase. This phenomenon is known as habituation, which causes the loss of control of robots and hinders their application in practical tasks such as search and rescue missions that require several hours. It has been shown that constantly switching the pattern of stimulus signals can slow down the onset of habituation. Moreover, when habituation occurs, applying a different stimulus signal can break the habituation. Based on this, we have designed a navigation algorithm that can extend the control time of insects to several hours. The algorithm is composed of a stimulation decision-making core responsible for deciding on the type of stimulus signal (left, right, acceleration), a stimulation parameters adjustment (SPA) core responsible for adjusting the stimulus signal voltage constantly to delay the occurrence of habituation, and a reactivation function (RF), as a different stimulus signal from the normal stimulus signal, is used to break insects' habituation to the normal stimulus signal. Experiments have shown that our SPA regulator and RF can significantly extend the control time of insects. Navigation experiments demonstrating effective control of the insects for up to 3 h verified the effectiveness of the navigation algorithm, which strikes a balance between control accuracy and control time.

The Sometimes Context-Specific Habituation: Theoretical Challenges to Associative Accounts

Simple Summary

When a stimulus occurs repeatedly without significant consequences, animals tend to decrease their responses to that stimulus. This phenomenon, known as habituation, can be explained by a class of theories that posit that expected events are less effective in provoking their responses than unexpected events. According to Allan Wagner’s priming theory, one of the ways this expectation might happen is via associative learning between the stimulus and the context in which stimulation occurred. In this article, we summarize a few theoretical complexities that derive from this approach along with some relevant empirical questions that remain open to further research.

Abstract

A substantial corpus of experimental research indicates that in many species, long-term habituation appears to depend on context–stimulus associations. Some authors have recently emphasized that this type of outcome supports Wagner’s priming theory, which affirms that responding is diminished when the eliciting stimulus is predicted by the context where the animal encountered that stimulus in the past. Although we agree with both the empirical reality of the phenomenon as well as the principled adequacy of the theory, we think that the available evidence is more provocative than conclusive and that there are a few nontrivial empirical and theoretical issues that need to be worked out by researchers in the future. In this paper, we comment on these issues within the framework of a quantitative version of priming theory, the SOP model.

Analysis of Habituation Learning in Mealworm Pupae (Tenebrio molitor)

The decline of response as a consequence of repeated stimulation is known as habituation. The goal of the present experiments was extending the knowledge about habituation of abdominal contractions in the pupa of Tenebrio molitor. Both experiments consisted of two phases. During Phase 1, all groups were exposed to a continuous stimulus (light in Experiment 1 and vibration in Experiment 2). At the beginning of this phase, pupae showed a high number of abdominal contractions. However, during the last minute of Phase 1, the number of abdominal contractions was lower. In the next phase, the pupae were divided in different groups to test for response recovery. We found an increase in the abdominal contractions when subjects were exposed to a different stimulus, be it within the same or in a distinct sensory modality. In addition, we also reported response recovery when the pupae were re-exposed to the original stimuli after a resting period. Results indicate that the increase in responding cannot be explained by either sensory adaptation or fatigue. The findings are consistent with the perspective that suggests that habituation plays a major role in the survival of the species, even in non-feeding developmental stages.

Effects of pre-exposure and post-exposure of the context in habituation of the retraction response in earthworms (Lumbricidae)

The context specificity of habituation has been demonstrated in earthworms. After the habituation of the retraction response to a light, a recovery of the response was observed when subjects are re-habituated in a different context. Some theories assume that an association between the context and the unconditioned stimulus could underlie this result. A series of experiments were conducted in order to test this issue. We assessed the potential disruptive effects of post-exposure (extinction effect) and pre-exposure of the context (latent inhibition effect) on the establishment of a context-US association. A recovery of response during subsequent rehabituation test was expected. The results of Experiment 1 showed that the extinction was effective, the post-exposure of the context after habituation produced a recovery of the retraction response. This result was replicated in Experiment 2 where the post-exposure condition was compared with a pre-exposure one. However, the pre-exposure to the context did not result in a recovery of the response in the rehabituation test, but also produced a general decrement on the response during the habituation training, that it has been interpreted as decrement in context's salience. In summary, these results suggest the involvement of associative and nonassociative processes in habituation learning.

Nicotine chronic tolerance development and withdrawal in the planaria (Schmidtea mediterranea)

Chronic nicotine exposure reduces sensitivity to the effects of nicotine, which then results in behavioural changes and tolerance development. In the planaria, a valuable first-stage preclinical model for addictive behaviour, acute nicotine administration has been shown to steadily alter the motility of the animals, a result that has been interpreted as evidence of tolerance and withdrawal effects; however, chronic exposure - typically regarded as a condition for the development of tolerance - and the role of the contextual cues have not been systematically assessed. The present study assessed the acute and chronic effects of nicotine on the motility of planarians (Schmidtea mediterranea). The animals in the experimental groups received long chronic exposure to nicotine (ten daily 30 min exposures); a control group was exposed to water in the same context but in the absence of the drug. The motility of the animals was closely monitored on every exposure. Following this phase, all the animals were subject to three different tests: in the presence of the exposure context (without the drug, Test 1); in the presence of nicotine in the exposure context (Test 2); and in the presence of the drug in a novel context (Test 3). Exposure to nicotine consistently reduced motility; the motility in the presence of nicotine increased with repeated exposures to the drug, an instance of tolerance development. Tolerance development was dependent on nicotinic receptor activation, because it was blocked by the co-administration of mecamylamine. However, this tolerance was found to be independent of the contextual cues where the effects of the drug had been experienced. The results are discussed by reference to the existent theories of tolerance development to drugs.