Figure 3. A posture-based analysis of locomotion responses to weak light stimuli.

(A) A diagram describing the repeated stimulus assay, in which a generic brief stimulus (vertical lines) was repeatedly delivered at 15 min intervals (long horizontal arrows). Each assay started at the mid L4int stage, continuously progressed through L4leth (shaded area), and ended at the mid YA stage. For the purpose of illustration, the blue and red lines symbolize tentative probabilities of forward locomotion and quiescence, respectively. Baseline behavior was measured during the 5-min period starting 10 min after a stimulus, or equivalently, 5 min prior to the subsequent stimulus. The beginning of the first baseline period is depicted by a dashed vertical line. (B) The fraction of forward locomotion, backward locomotion, dwelling, and quiescence before, during, and after a weak (15 s, 20 mW/cm² blue light) stimulus provided at the L4int (left), L4leth (middle), and YA (right) stages. A compensatory post-stimulus enhancement of quiescence, as well as enhanced reversals during the stimulus, and a rising propensity for forward locomotion after the stimulus was turned off were uniquely observed during lethargus. Insets: the fraction of forward locomotion before and after the offset of the stimulus (top) and the fraction of backward locomotion before and after the onset of the stimulus. Shading denotes the presence of the light stimulus. All fractions were calculated from the 7.5-s period (half of the duration of the stimulus), the scale bars represent a fraction of 0.5, and asterisks denote p < 0.05. (C) The data from the middle panel of (B) plotted separately for the first, second, and third hours of L4leth. Enhanced quiescence was observed in all three cases, although it was less prominent during the third hour. Plots in panels (B, C) depict mean ± s.e.m and the number of stimuli assayed is noted in parentheses for each condition.

DOI: http://dx.doi.org/10.7554/eLife.04380.008

Figure 3—figure supplement 1. The averaged behavior data have periodic boundaries.

Each sketched closed curve represents the average fraction of quiescence as a function of time for a particular set of experimental conditions. Since repeated 15-min cycles were aligned and averaged, the mean behavioral dynamics have periodic boundaries. Graphically, this can be represented by plotting the data on a circular time axis, where the onset of the stimulus is denoted by an asterisk. During lethargus, the immediate response to a stimulus lasted no more than 3 min. After this short-term response was complete, the fraction of quiescence returned to a steady state that was characteristic of the conditions of the experiment. The fraction of time spent is quiescence during this steady state was defined as the baseline level of quiescence for the relevant experimental conditions. In this framework, baselines were compared between different conditions. Left: responses to strong stimuli. The immediate response to a strong stimulus is depicted by the yellow curve and the baselines for periodically stimulated and undisturbed animals are depicted by brown and grey curves, respectively. Elevation of the steady state quiescence—as compared to the mean quiescence of undisturbed animals—constituted the sustained response to the presence of repeated strong stimuli. This elevation is emphasized by a double-headed arrow. Right: responses to weak stimuli. The immediate response to a weak stimulus is depicted by the orange curve and the baselines for periodically stimulated and undisturbed animals are depicted by blue and grey curves, respectively.

DOI: http://dx.doi.org/10.7554/eLife.04380.009