Understanding the physiology of behavior has been hampered for a long time by the technical limitations to analyze behavior in great detail and to measure physiological processes in freely behaving animals and human beings. However, recent developments in technology have created fascinating possibilities for the advancement of research in the field of behavioral physiology. This introductory lecture will illustrate some of this progress on the basis of our own research on the behavioral physiology of social behavior in rats and mice.

Rats and mice live in rather complex social structures in which individuals differ in their social relations to other group members. The social structure is maintained by agonistic behavior. Studies in wild populations of mice indicate that the level of agonistic behavior is bimodally distributed over the individual group members. Extensive behavioral research indicates that the distribution of agonistic behavior reflects a more general individual differentiation in coping style. Aggressive males adopt a proactive coping style in a wide variety of challenging situations, whereas the non aggressive males in the population appear to adopt a reactive coping style. Our research focuses on this individual differentiation in coping style because it reflects not only a differentiation in vulnerability to stress mediated diseases, but also a differentiation in central nervous and neuroendocrine mechanisms.

The methodology used and the need for further methodological developments will be illustrated briefly in three lines of our research. The first line of research tests the hypothesis that a fundamental behavioral difference between the two coping styles concerns the degree in which behavior is self-controlled or guided by or depends on environmental stimuli. This is studied by a detailed transition analysis of a social interaction between a resident and the intruder in its home cage, using frame-by-frame analysis of video recordings. A second line of research concerns the question to what extent the social structure of a group of male rats, its stability and the development of stress pathology depend on the composition of the group in terms of coping styles. This study uses video tracking methods to monitor the social structure and radiotelemetry to measure physiological parameters in group-housed rats. A third line of research aims at understanding the long term (weeks and months) behavioral and physiological consequences of a single social defeat experience. In view of the duration of the effects, these studies require various automated recording techniques for behavior and physiology.

The three lines of research have in common the need for advanced in vivo brain imaging techniques with a sufficient resolution in space and time. Moreover, the advancement of automated recording techniques of behavior and physiology generates an exponential increase in the amount of data. Efficient handling, reduction and integration of these large data sets will be a major challenge for the near future.