Honest signaling in mouse lemur vocalizations?

Animal vocalizations may provide information about a sender’s condition or motivational state and, hence, mediate social interactions. In this study, we examined whether vocalizations of gray mouse lemurs (Microcebus murinus) emitted in aggressive contexts (grunts, tsaks) co-vary with physical condition, which would underly and indicate honest signaling. We recorded calls from captive individuals that were subjected to a caloric restricted (CR) or ad libitum (AL) diet, assuming that individuals on an ad libitum dietary regime were in better condition. We analyzed 828 grunts produced by seven CR and nine AL individuals and 270 tsaks by eight CR and five AL individuals. Grunts consisted of two separate elements, with the 1st element having more energy in higher frequencies than the 2nd element. Body mass correlated negatively with acoustic features of grunts, and heavier individuals produced lower-frequency grunts. Acoustic features of grunts did not differ between sexes. Acoustic features of tsaks were predicted by neither body mass nor sex. However, tsaks produced by AL individuals were noisier than those of CR individuals. Hence, manipulation of body condition via dietary regimes affected acoustic features of calls given during aggression in different ways: acoustic features of grunts varied according to the rule of acoustic allometry, and can be considered as honest signals. Acoustic features of tsaks, however, varied according to motivational structural rules. Longitudinal studies are now indicated to examine whether intra-individual changes in body mass are also reflected in the acoustic structure of calls, allowing callers to signal more flexible variation in condition.

Activation of LH GABAergic inputs counteracts fasting-induced changes in tVTA/RMTG neurons.

Dopamine neurons in the ventral tegmental area (VTA) are strongly innervated by GABAergic neurons in the tail of the VTA (tVTA), also known as the rostralmedial tegmental nucleus (RMTg). Disinhibition of dopamine neurons through firing of the GABAergic neurons projecting from the lateral hypothalamus (LH) leads to reward seeking and consumption through dopamine release in the nucleus accumbens. VTA dopamine neurons respond to changes in motivational state, yet less is known of whether tVTA/RMTg GABAergic neurons or the LH GABAergic neurons that project to them are also affected by changes in motivational state, such as fasting. An acute 16 h overnight fast decreased the excitability of tVTA/RMTg GABAergic neurons of male and female mice. In addition, fasting decreased synaptic strength at LH GABA to tVTA/RMTg GABAergic synapses, indicated by reduced amplitude of optically evoked currents, decreased readily releasable pool (RRP) size and replenishment. Optical stimulation of LH GABA terminals suppressed evoked action potentials of tVTA/RMTg GABAergic neurons in unfasted mice, but this effect decreased following fasting in both males and females. Furthermore, during fasting, LH GABA inputs to tVTA/RMTg neurons maintained functional connectivity during depolarization, as depolarization block was reduced following fasting. Taken together, inhibitory synaptic transmission from LH GABA inputs onto tVTA/RMTg GABAergic neurons decreases following fasting, however ability to functionally inhibit tVTA/RMTg GABAergic neurons is preserved, allowing for possible disinhibition of dopamine neurons and subsequent foraging.

A Diary Study on Anticipated Leisure Time, Morning Recovery and Employees’ Work Engagement

Recovery during yesterday’s leisure time is beneficial for morning recovery, and morning recovery fosters employees’ work engagement, a positive, motivational state associated with job performance. We extended existing research by assuming that both, morning recovery (considered a resource) and anticipated leisure time (considered an anticipated resource gain), relate to work engagement. Anticipated leisure time comprises two constructs: general anticipation of leisure time, which refers to employees’ cognitive evaluation of their entire upcoming leisure time, and pleasant anticipation of a planned leisure activity, which describes a positive affective reaction because of one specific, upcoming leisure activity. We suggested that employees with high pleasant anticipation generate more thoughts of a planned leisure activity (ToPLA), which may distract them from their work, reducing their work engagement. A diary study over five days showed that morning recovery and general anticipation of leisure time were positively related to work engagement. Furthermore, employees with higher pleasant anticipation of a planned leisure activity reported more ToPLA. In contrast to our expectations, neither pleasant anticipation nor ToPLA was related to work engagement. In sum, this study introduced anticipated leisure time as a novel antecedent of work engagement and demonstrated that anticipated resource gains are important for high work engagement.

Olfactory perceptual decision-making is biased by motivational state

Growing evidence suggests that internal factors influence how we perceive the world. However, it remains unclear whether and how motivational states, such as hunger and satiety, regulate perceptual decision-making in the olfactory domain. Here, we developed a novel behavioral task involving mixtures of food and nonfood odors (i.e., cinnamon bun and cedar; pizza and pine) to assess olfactory perceptual decision-making in humans. Participants completed the task before and after eating a meal that matched one of the food odors, allowing us to compare perception of meal-matched and non-matched odors across fasted and sated states. We found that participants were less likely to perceive meal-matched, but not non-matched, odors as food dominant in the sated state. Moreover, functional magnetic resonance imaging (fMRI) data revealed neural changes that paralleled these behavioral effects. Namely, odor-evoked fMRI responses in olfactory/limbic brain regions were altered after the meal, such that neural patterns for meal-matched odor pairs were less discriminable and less food-like than their non-matched counterparts. Our findings demonstrate that olfactory perceptual decision-making is biased by motivational state in an odor-specific manner and highlight a potential brain mechanism underlying this adaptive behavior.

An ecological approach to measuring synchronization abilities across the animal kingdom

In this perspective paper, we focus on the study of synchronization abilities across the animal kingdom. We propose an ecological approach to studying nonhuman animal synchronization that begins from observations about when, how and why an animal might synchronize spontaneously with natural environmental rhythms. We discuss what we consider to be the most important, but thus far largely understudied, temporal, physical, perceptual and motivational constraints that must be taken into account when designing experiments to test synchronization in nonhuman animals. First and foremost, different species are likely to be sensitive to and therefore capable of synchronizing at different timescales. We also argue that it is fruitful to consider the latent flexibility of animal synchronization. Finally, we discuss the importance of an animal's motivational state for showcasing synchronization abilities. We demonstrate that the likelihood that an animal can successfully synchronize with an environmental rhythm is context-dependent and suggest that the list of species capable of synchronization is likely to grow when tested with ecologically honest, species-tuned experiments. This article is part of the theme issue ‘Synchrony and rhythm interaction: from the brain to behavioural ecology’.

Evaluating the accuracy of facial expressions as emotion indicators across contexts in dogs

Facial expressions potentially serve as indicators of animal emotions if they are consistently present across situations that (likely) elicit the same emotional state. In a previous study, we used the Dog Facial Action Coding System (DogFACS) to identify facial expressions in dogs associated with conditions presumably eliciting positive anticipation (expectation of a food reward) and frustration (prevention of access to the food). Our first aim here was to identify facial expressions of positive anticipation and frustration in dogs that are context-independent (and thus have potential as emotion indicators) and to distinguish them from expressions that are reward-specific (and thus might relate to a motivational state associated with the expected reward). Therefore, we tested a new sample of 28 dogs with a similar set-up designed to induce positive anticipation (positive condition) and frustration (negative condition) in two reward contexts: food and toys. The previous results were replicated: Ears adductor was associated with the positive condition and Ears flattener, Blink, Lips part, Jaw drop, and Nose lick with the negative condition. Four additional facial actions were also more common in the negative condition. All actions except the Upper lip raiser were independent of reward type. Our second aim was to assess basic measures of diagnostic accuracy for the potential emotion indicators. Ears flattener and Ears downward had relatively high sensitivity but low specificity, whereas the opposite was the case for the other negative correlates. Ears adductor had excellent specificity but low sensitivity. If the identified facial expressions were to be used individually as diagnostic indicators, none would allow consistent correct classifications of the associated emotion. Diagnostic accuracy measures are an essential feature for validity assessments of potential indicators of animal emotion.

Selective Devaluation Affects the Processing of Preferred Rewards

The present study investigated whether the representation of subjective preferences in the event-related potential is manipulable through selective devaluation, i.e., the consumption of a specific food item until satiety. Thirty-four participants completed a gambling task in which they chose between virtual doors to find one of three snack items, representing a high, medium, or low preference outcome as defined by individual desire-to-eat ratings. In one of two test sessions, they underwent selective devaluation of the high preference outcome. In the other, they completed the task on an empty stomach. Consistent with previous findings, averaged across sessions, amplitudes were increased for more preferred rewards in the time windows of P2, late FRN, and P300. As hypothesised, we also found a selective devaluation effect for the high preference outcome in the P300 time window, reflected in a decrease in amplitude. The present results provide evidence for modulations of reward processing not only by individual factors, such as subjective preferences, but also by the current motivational state. Importantly, the present data suggest that selective devaluation effects in the P300 may be a promising tool to further characterise altered valuation of food rewards in the context of eating disorders and obesity.

Injury alters motivational trade-offs in calves during the healing period

Injury can produce long-lasting motivational changes that may alter decisions made under risk. Our objective was to determine whether a routine painful husbandry procedure, hot-iron disbudding, affects how calves trade off risk avoidance against a competing motivation (i.e., feeding), and whether this response depends on time since injury. We used a startle test to evaluate this trade-off in calves disbudded 0 or 21 days previously and non-injured control calves. For 3 days, calves were individually habituated to the testing arena in which they received a 0.5 L milk meal via a rubber teat. On the 4thday, upon approaching the milk reward, the calf was startled by a sudden noise. We assessed the duration and magnitude of the calf’s startle response, their latency to return to the milk bottle, and duration spent suckling after startling. No treatment differences were observed in the duration and magnitude of the startle response or in the probability of returning to the bottle after startling. However, among those who did return, disbudded calves spent longer suckling, indicating they accepted more risk in order to feed compared to controls. In addition, calves with 21-day-old injuries tended to return to the bottle faster compared to newly disbudded calves and controls. We suggest that hot-iron disbudding increases calves’ motivation to suckle, as they were more likely to prioritize this behaviour over risk avoidance compared to control calves. This effect was most evident 21 days after disbudding, indicating that injury can produce long-term changes in motivational state.

Devaluation of a conditioned reinforcer requires its reexposure

A change in motivational state does not guarantee a change in operant behaviour. Only after an organism has had contact with an outcome while in a relevant motivational state does behaviour change, a phenomenon called incentive learning. While ample evidence indicates that this is true for primary reinforcers, it has not been established for conditioned reinforcers. We performed an experiment with rats where lever-presses were reinforced by presentations of an audiovisual stimulus that had previously preceded food delivery; in the critical experimental groups, the audiovisual stimulus was then paired a single time with a strong electric shock. Some animals were reexposed to the audiovisual stimulus. Lever-presses yielding no outcomes were recorded in a subsequent test. Animals that had been reexposed to the audiovisual stimulus after the aversive training responded less than did those that had not received reexposure. Indeed, those animals that were not reexposed did not differ from a control group that received no aversive conditioning of the audiovisual stimulus. Moreover, these results were not mediated by a change in the food’s reinforcement value, but instead reflect a change in behaviour with respect to the conditioned reinforcer itself. These are the first data to indicate that the affective value of conditioned stimuli, like that of unconditioned ones, is established when the organism comes into contact with them.