Abstract
Most behaviors such as making tea are not stereotypical but have an obvious structure. However, analytical methods to objectively extract structure from non-stereotyped behaviors are immature. In this study, we analyze the locomotion of fruit flies and show that this non-stereotyped behavior is well-described by a Hierarchical Hidden Markov Model (HHMM). HHMM shows that a fly's locomotion can be decomposed into a few locomotor features, and odors modulate locomotion by altering the time a fly spends performing different locomotor features. Importantly, although all flies in our dataset use the same set of locomotor features, individual flies vary considerably in how often they employ a given locomotor feature, and how this usage is modulated by odor. This variation is so large that the behavior of individual flies is best understood as being grouped into at least three to five distinct clusters, rather than variations around an average fly.
Highlights
There are many approaches to the study of neural underpinnings of behavior: One large body of work is rooted in the psychophysical literature where an animal is forced to choose between a few discrete behaviors (Green and Swets, 1974)
Many of these relatively stereotypical behavioral motifs are at play during most behaviors, they are not helpful in describing the structure underlying most everyday activities such as making a cup of coffee or a peanut-butter sandwich or walking to a car which consist of a sequence of actions, but neither the sequence nor each sub-action is stereotyped
We show that fly locomotion is well-structured and an Hierarchical Hidden Markov Model (HHMM) is an elegant representation of this structure
Summary
There are many approaches to the study of neural underpinnings of behavior: One large body of work is rooted in the psychophysical literature where an animal is forced to choose between a few discrete behaviors (Green and Swets, 1974). Other studies have focused on behaviors that are reflexive (albeit with some flexibility) such as saccades (Laurutis and Robinson, 1986) and collision avoidance in insects (Tammero and Dickinson, 2002) Another large body of work has focused on the control processes involved in goal-directed behaviors such as reaching movements and has revealed many fundamental principles of motor control. Much work has been done to elucidate the workings of central pattern generators that underlie the rhythmic motor activity during walking and running (Grillner, 1979) Many of these relatively stereotypical behavioral motifs are at play during most behaviors, they are not helpful in describing the structure underlying most everyday activities such as making a cup of coffee or a peanut-butter sandwich or walking to a car which consist of a sequence of actions, but neither the sequence nor each sub-action is stereotyped. While tracks of a mouse or a fly exploring a chamber are not stereotypical there is an obvious structure to it
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