The Coordination between the Direction of Progression and Body Orientation in Normal, Alcohol- and Cocaine Treated Fruit Flies

In studying the gene/brain/behavior relationship, detailed quantitative descriptions of the behavior of the animal's behavior is required. Especially important are descriptions of behavior in terms of the dynamics of the coordination between the direction of progression of the animal and the animal’s body orientation, for these provide fundamental insight into motor control. For mouse locomotor behavior these measures have been welldeveloped, yet such descriptions are still sparse for Drosophila, the model system of choice for behavior geneticists. Here we present a dynamic description of the coordination between these two variables, as they change throughout different temporal segments of the motion. Methodology/Principal Findings Using intrinsic statistical and geometrical properties of a fly’s movement, we have uncovered six fundamental modes of motion related to translation and rotation of a fly’s body. Assignment of the frame-by-frame instantaneous movement into one of the six modes, followed by clustering and algorithmic classification, allows us to quantify the behavior in terms of the proportions and dynamic sequencing of each mode. The analysis uncovered that for normal flies, the angle between the direction the animal walks and the direction it faces is quite small. Under the influence of alcohol and cocaine, however, the angular interval between these two variables increases. Conclusions/Significance For several decades the representation of movement, indispensable for studying the interface between genes brain and behavior, suffered from the use of ad hoc building blocks such as “behavior patterns” or “response categories” assumed to be performed unblock by the whole organism, one at a time. The ethological and psychological schools using such representations, were based on expert (indeed, subjective) decisions. In the vast majority these alleged building blocks could not be shown to have a physiological reality in the brain; the school using them has been described as the “school of immaculate perception”. These ad hoc units were used as “black boxes” and their variable kinematic content has been disregarded. Disregarding the coordination between translation and rotation, for example, sidestepped the problem of coordination, which is at the heart of the brain/behavior interface. The huge progress in tracking and storing technology allowed the recording of continuous kinematic variables such as the location and orientation of the organism, thus bringing about a most significant change, allowing, for the first time, the study of coordination between these variables in long stretches of behavior lasting hours or even days. This time scale is necessary for the study of e.g., drug effects on behavior, or for the phenotyping of genetic mutants exploratory and locomotor behavior. The pioneers utilizing this technology use, however, the