ReviewAnimal models of human psychopathology based on individual differences in novelty-seeking and anxiety
Introduction
Quantitative individual behavioural differences were not systematically addressed until the late 18th century when interest was directed to the ‘personal equations’ used by astronomers for measuring stellar transits. Then, scientists discovered not only differences between individuals, but also that the individual's ‘personal equation’ also varied over time, suggesting that the rather large individual differences were not invariant. These differences involved visual as well as auditory reaction times, and attention and vigilance also played a role (Anastasi 1958, cited from Brush, 1991). Today, one of the major challenges of personality research is to understand the causes of individual differences and their consequences in terms of fitness, adaptive capacity, and individual vulnerability to diseases. Animal research has also been used to investigate individuality. Thus, there is a range of methods that can be applied in different species (for review see Gosling, 2001). In this literature, individuality is defined as a collection of behavioural or physiological traits, both innate and acquired, that distinguish one individual from near relatives, which as far as possible share the same genetic and environmental background.
The role of individual difference factors in behavioural neuroscience is an important, but still neglected area of research. One problem is the need for higher numbers of participants or subjects than the commonly used approach. Accordingly, research issues requiring many subjects (e.g., dose–response effects) are often neglected in favour of less demanding inquiries. In the last years, however, the necessity of an individual approach for research on biology/behaviour relationships has become more and more important. Despite the progress in examining biopsychological processes in humans, behavioural neuroscience in animals remains indispensable. For example, do animals show substantial differences in behaviour, physiology, or pharmacological reactivity? What are the relationships between these parameters and how consistent are they? What are the key domains of individual behavioural differences that have physiological relevance? More importantly, can these domains predict a priori the outcome of experimental manipulations? To what extent do certain stable characteristics of the organism shape physiological outcomes, before and after experimental manipulations? These questions are important to answer if animal models of diseases are to be developed in order to investigate in depth individual susceptibility to diseases or psychiatric disorders.
The present review aims, first, to give an outline of some of the most important theories of individual behaviours in animals and humans, and second, an overview of all systematic approaches of historic and present animal models of human psychopathology based on individual differences in novelty-seeking and anxiety, to the best knowledge of the authors. It was our intention to include all systematic animal models relating to anxiety and novelty-seeking within one review for the first time. Finally, critical aspects of studying individual behaviour in animals are discussed, and suggestions are given where to go from here.
Section snippets
Theories of individual behaviour
It is out of the scope of this work to provide a comprehensive overview of the most relevant biopsychological theories of individual behaviour in animals (e.g., Depue and Lenzenweger, 2005, Gray and McNaughton, 2000, McNaughton and Corr, 2004, White and Depue, 1999), and human personality (Cloninger, 2003, Zuckerman, 1984; for overviews see Amelang et al., 2006, Hennig and Netter, 2005, McAdams, 2001, Pervin and John, 2001). But one of the most influential theories on the neurobehavioural
Individuality in animal models
For a number of decades it has been the aim of several research groups to establish methodologies to assess behavioural traits in animals and to differentiate between conspecifics of a given species. “Trait” is defined here as a pattern of a specific behaviour, which differs between individuals, but which is relatively constant within subjects over time and situations (Amelang et al., 2006). This term is usually used in animal behavioural research instead of “personality” in humans.
High responder (HR) and low responder (LR) rats
Piazza et al. (1989) provided substantial evidence to demonstrate that (A) individuals within an animal laboratory differ widely in their reactivity to forced novelty exploration and (B) that this difference may be useful to predict individual differences in sensitivity to drugs of abuse. They showed that unselected male Sprague–Dawley rats differed in their response to a novel environment, which predicted individual differences in response to the psychostimulant drug amphetamine. In detail, a
Anxiety and fear as two distinct behavioural systems
The use of the word “anxiety” dates back to Middle High German, and “fear” dates back to the Old German period (Paul, 2006). Both words were used in different context: “Fear” often in combination with, for example, religious issues, and “anxiety” linked with misery, pain, and affliction (Paul, 2006). Personality researchers nowadays have acknowledged that anxiety and fear are two distinct behavioural systems (Depue and Lenzenweger, 2005, Gray and McNaughton, 2000, McNaughton and Corr, 2004,
Conclusion
In the future, the individual approach to study behaviour of laboratory animals has to play a more important role than before. Likewise as shown in research with humans and experienced in encounters in daily life with humans, animals also simply do not react uniformly to the same stimulus. It is a must to distinguish between individual subjects, and to select subgroups of animals in a given population that are particularly reactive and are thus readily transformed in different emotional states
Suggestions for future research
At first sight, the open field and the elevated plus-maze, on which most approaches of individuality in rodents are based, appear to be thoroughly characterised and effective for understanding clinically relevant problems, but a number of issues remain to be addressed. One stems from the lack of sufficient studies on long-term effects of drugs. Another issue concerns a need for more precise validity of the models for human disorders as postulated by Willner (1991), and Willner and Mitchell
Acknowledgements
We are indebted to Dr. Ron Mucha for carefully revising an earlier version of this manuscript. We also like to thank two anonymous reviewers for their helpful comments.
This work was supported by grants from the Project Based Personnel Exchange Programme (0940042882 from the NSC and D/05/06869 from the German Academic Exchange Service DAAD), and the German Research Foundation (DFG PA 818/4-1).
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