A single brief cue leaves a day-long internal state imprint in planarians.

Abstract

Behavioral decisions are elicited by environmental stimuli, but they are critically modulated by internal states. Persistent state-dependent biases are typically attributed to accumulated sensory history, high-intensity stimulation, or sustained environmental conditions. However, organisms also encounter isolated, innocuous perturbations whose long-term impacts remain poorly understood. Here, we show that a single brief mechanical cue induces changes in spontaneous locomotor activity in the planarian <i>Dugesia japonica</i> that persist over a day-long timescale. This cue specifically shortened rest bouts without altering within-bout movement kinematics, indicating a targeted shift in the transition probability out of rest rather than a general upregulation of motor activity. Furthermore, as this day-scale effect decayed, an underlying ultradian alternation in activity persisted. Our results demonstrate that postcue behavioral organization adopts a two-timescale structure, combining day-scale persistence with multihour patterning. This dual-layer architecture provides an empirical basis for understanding how a single environmental encounter can reprogram long-term behavioral patterns without further sensory input, extending the temporal reach of even compact nervous systems.