A concept of welfare based on reward evaluating mechanisms in the brain: anticipatory behaviour as an indicator for the state of reward systems

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Abstract

In this review we attempt to link the efficiency by which animals behave (economy of animal behaviour) to a neuronal substrate and subjective states to arrive at a definition of animal welfare which broadens the scope of its study. Welfare is defined as the balance between positive (reward, satisfaction) and negative (stress) experiences or affective states. The state of this balance may range from positive (good welfare) to negative (poor welfare). These affective states are momentary or transient states which occur against the background of and are integrated with the state of this balancing system. As will be argued the efficiency in behaviour requires that, for instance, satisfaction is like a moving target: reward provides the necessary feedback to guide behaviour; it is a not steady-state which can be maintained for long. This balancing system is reflected in the brain by the concerted action of opioid and mesolimbic dopaminergic systems. The state of this system reflects the coping capacity of the animal and is determined by previous events. In other words, this integrative approach of behavioural biology and neurobiology aims at understanding how the coping capacity of animals may be affected and measured. We argue that this balancing system underlies the economy of behaviour. Furthermore we argue that among other techniques anticipation in Pavlovian conditioning is an easy and useful tool to assess the state of this balancing system: for estimating the state of an animal in terms of welfare we focus on the conditions when an animal is facing a challenge.

Section snippets

Introduction: the economy of behaviour

Living organisms in general, and vertebrates in particular, have achieved a remarkable efficiency in using environmental resources and avoiding potentially harmful stimuli and situations. Behavioural ecologists (see Krebs and Davies (1993) for a review) have captured such efficiency in models which are partly derived from and related to the field of human economy: the relation between the investment of an organism on the one hand and the consequences of its actions on the other can be

Motivational systems

Although the aforementioned studies are clearly able to indicate that such efficient mechanisms operate in a given species it is through the study of the causal analysis or proximate causation of how these mechanisms achieve efficiency and operate, that it becomes conceivable why individuals act in the way they do at any particular point in time. Such causal analysis at the same time allows one to consider constraints of these mechanisms whether due to ontogenetical or environmental factors.

Expected consequences in terms of reward: maximising profit of ongoing behaviour

Ethologically oriented descriptions of motivational systems implicitly seem to assume that the rewarding value of a commodity is selected over generations, i.e. is genetically anchored. This is, for instance, true in the case of milk-drinking in new born animals. This can only be achieved under stable microenvironments, which the early phase of the mother–new-born bond for instance is. However, once animals mature and start to eat other food-items they learn the rewarding value of different

Supervising systems: welfare

From the foregoing delineation of a hierarchically organised reward (likingwanting) system we arrive at a definition of animal welfare. We define pleasure or satisfaction as a transient state when the animal has reduced the difference between actual and expected (reference) state (cf. Wiepkema, 1985). It is transient, as other motivational systems may call for attention of which the actual and expected state are not in line. Similarly we define displeasure (stress) as the (perceived) inability

Anticipatory behaviour: a general expression of the animal’s need

If opioids have an overall function related to the rewarding properties independent of the nature of the reward, then their activation might result into a display of reward related characteristic behavioural patterns. The display of such behavioural patterns in anticipation of a reward is presumably the result of the postulated release of endorphins and dopamine. These behavioural patterns bear similarity to behavioural patterns induced by a low dose of opioids especially. The earliest

Conclusion

Monitoring ongoing and already performed behaviour is a necessity for organisms with the ability to learn and adapt. We propose welfare to be a balance of rewarding and aversive events. Some stressful conditions can be counteracted by the perspective of successful coping or can be partly compensated by other rewarding events. On the other hand deprivation of a single essential need might be crucial whatever the possibilities of other rewards. The plasticity of various needs depends on

Acknowledgements

We would like to thank Prof. Piet Wiepkema (Oosterbeek, The Netherlands), Dr. Georgia Mason (Oxford University, UK) and Prof. Michel Cabanac (Université Laval, Canada) as well as two anonymous referees for helpful comments on the manuscript. Furthermore we would like to thank Mrs. Irene Bos for her secretarial help.

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