The concepts want, hope, and exploration cannot be organized in relation to a single type of motive (e.g., motive for food). They require, in addition, the motive for acquiring and maintaining a stable scheme that enables reward-directed activity. Facing unpredictability, the animal has to seek not only reward, but also a new equilibrated state within which reward seeking is possible.

In the theory outlined in the target article, an animal forages continuously, making sequential decisions in a world where the amount of food and its uncertainty are fixed, but delays are variable. These assumptions contrast with the risk-sensitive foraging theory and create a problem for comparing the predictions of this model with many laboratory experiments that do not make these assumptions.

We argue that How Foraging Works sketches a good foundational model, but it needs expanding to incorporate hierarchical and multiscale conceptions of uncertainty and to incorporate inference of environmental controllability. Most pressingly, its algorithmic implementation needs to be better justified in terms of its functional forms and, ultimately, to be more heavily constrained by survival optimality.

We propose that food-related uncertainty is but one of multiple cues that predicts harsh conditions and may activate “incentive hope.” An evolutionarily adaptive response to these would have been to shift to a behavioral-metabolic phenotype geared toward facing hardship. In modernity, this phenotype may lead to pathologies such as obesity and hoarding. Our perspective suggests a novel therapeutic approach.

Uncertainty is caused not only by environmental changes, but also by social interference resulting from competition over food resources. Actually, foraging effort is socially facilitated, which, however, does not require incentive control by the dopamine system; Zajonc's “drive” theory is thus questionable. Instead, social adjustments may be pre-embedded in the limbic network responsible for decisions of appropriate effort-cost investment.

In this commentary, we discuss how the “incentive hope” hypothesis explains differences in food-wasting behaviors among humans. We stress that the role of relevant ecological characteristics should be taken into consideration together with the incentive hope hypothesis: population mobility, animal domestication, and food-wasting visibility.

We discuss how uncertainty underwrites exploration and epistemic foraging from the perspective of active inference: a generic scheme that places pragmatic (utility maximization) and epistemic (uncertainty minimization) imperatives on an equal footing – as primary determinants of proximal behavior. This formulation contextualizes the complementary motivational incentives for reward-related stimuli and environmental uncertainty, offering a normative treatment of their trade-off.

The amplification of reward-seeking behavior under uncertainty described by Anselme & Güntürkün is based on the animal literature. However, this phenomenon could provide valuable information for the understanding of several dysfunctional human behaviors such as overeating and gambling. Therefore, we formulated some considerations on how the “incentive hope” hypothesis could be tested on a human population.

Commonly used measures of human food insecurity differ categorically from measures determining food security in other species. In addition, human foraging behaviors may have arisen in a divergent evolutionary context from nonhuman foraging. Hence, a theoretical framework based on food insecurity and fat storage in nonhumans may not be appropriate for explaining associations between human food insecurity and obesity.

Predictions made by the “incentive hope” hypothesis account for overconsumption in unpredictable food environments. However, when applied to uncertain gambling situations, there are several areas where this theory falls short. Most notably, it has trouble explaining why, in slot machine gambling, players are motivated by extended play to spend time trying to resolve uncertainty, rather than hoarding monetary gains.

Anselme & Güntürkün propose a novel mechanism to explain the increase in foraging motivation when experiencing an unpredictable food supply. However, the physiological mechanisms that maintain energy homeostasis already control foraging intensity in response to changes in energy balance. Therefore, unpredictability may just be one of many factors that feeds into the same dopaminergic “wanting” system to control foraging intensity.

The target article addresses increased food-seeking behaviors in times of instability, particularly in passerines. We note that food instability might have intergenerational effects on birds: Nutritional stress during development affects song-learning abilities, associating parental foraging with offspring sexual selection. We explore the implications of these compounding selection pressures on food-seeking motivation during breeding, as well as the hormonal underpinnings of these behaviors.

Anselme & Güntürkün generate exciting new insights by integrating two disparate fields to explain why uncertain rewards produce strong motivational effects. Their conclusions are developed in a framework that assumes a random distribution of resources, uncommon in the natural environment. We argue that, by considering a realistically clumped spatiotemporal distribution of resources, their conclusions will be stronger and more complete.

Positioning “incentive hope” in a general model of behavioral control systems removes artificial boundaries between mechanisms of incentive motivation in foraging behavior and other functions of the striatum and connected systems. Specifically, incentive hope may involve mechanisms of anticipation of both reward and threat, explaining why anxious individuals show stronger potentiation of incentive motivation under conditions of reward uncertainty.

Low-income environments have been associated with greater levels of impulsive behavior, which contribute to the higher debt and obesity rates that further perpetuate current wealth and health disparities. In this commentary, we describe how this might be explained by an appeal to “incentive hope” and the motivational drive toward consumption triggered by the future uncertainty these groups face.

Information seeking, especially when motivated by strategic learning and intrinsic curiosity, could render the new mechanism “incentive hope” proposed by Anselme & Güntürkün sufficient, but not necessary to explain how reward uncertainty promotes reward seeking and consumption. Naturalistic and foraging-like tasks can help parse motivational processes that bridge learning and foraging behaviors and identify their neural underpinnings.

The “incentive hope” model creatively explains hoarding and fat accumulation by foragers under uncertainty and food seeking when food cues are present but food is not. The model has difficulty explaining why animals driven by cues fare better than animals driven by food reward itself, why human obesity exists when food is abundant, and why people enjoy gambling and care about winning.

Our target article proposes that a new concept – incentive hope – is necessary in the behavioral sciences to explain animal foraging under harsh environmental conditions. Incentive hope refers to a specific motivational mechanism in the brain – considered only in mammals and birds. But it can also be understood at a functional level, as an adaptive behavioral strategy that contributes to improve survival. Thus, this concept is an attempt to bridge across different research fields such as behavioral psychology, reward neuroscience, and behavioral ecology. Many commentaries suggest that incentive hope even could help understand phenomena beyond these research fields, including food wasting and food sharing, mental energy conservation, diverse psychopathologies, irrational decisions in invertebrates, and some aspects of evolution by means of sexual selection. We are favorable to such extensions because incentive hope denotes an unconscious process capable of working against many forms of adversity; organisms do not need to hope as a subjective feeling, but to behave as if they had this feeling. In our response, we carefully discuss each suggestion and criticism and reiterate the importance of having a theory accounting for motivation under reward uncertainty.

Microbiota-gut-brain (MGB) research is a fast-growing field of inquiry with important implications for how human brain function and behaviour are understood. Researchers manipulate gut microbes (“microbiota”) to reveal connections between intestinal microbiota and normal brain functions (e.g., cognition, emotion, and memory) or pathological states (e.g., anxiety, mood disorders, and neural developmental disorders such as autism). Many claims are made about causal relationships between gut microbiota and human behaviour. By uncovering these relationships, MGB research aims to offer new explanations of mental health and potential avenues of treatment.

So far, limited evaluation has been made of MGB's methods and its core experimental findings, many of which are extensively reiterated in copious reviews of the field. These factors, plus the self-help potential of MGB, have combined to encourage uncritical public uptake of MGB discoveries. Both social and professional media focus on the potential for dietary intervention in mental health, and causal relationships are assumed to be established.

Our target article has two main aims. One is to examine critically the core practices and findings of experimental MGB research and to raise questions about them for brain and behavioural scientists who may not be familiar with the field. The other is to challenge the way in which MGB findings are presented. Our positive goal is to suggest how current problems and weaknesses may be addressed, in order for both scientific and public audiences to gain a clearer picture of MGB research and its strengths and limitations.