Toward an understanding of the neurobiology of "just right" perceptions: nest building in the female rabbit as a possible model for compulsive behavior and the perception of task completion.

Little is known of the neural mechanisms underlying the subjective experience of task completion and the subsequent inhibition of behavior. The preparturient female rabbit displays a stereotyped "straw carrying" behavior, in which she repeatedly collects straw and carries it into a nest box (located within the home cage), resulting in a finished maternal straw nest within 3 h. Thereafter, straw carrying is inhibited for many hours, even if the original nest is removed. We tested whether the performance of straw carrying behavior or the perception of a completed nest were necessary prerequisites for the engagement of this inhibitory mechanism. On day 28 of pregnancy, we placed straw inside the home cage (at t=0 h) and recorded the female's behavior for 3 h, at which time the nest was removed from the nest box. Multiparous females began to collect straw almost immediately, whereas inexperienced females were delayed in this respect. In females that had perceived a completed nest inside the nest box during t=0-3 h, straw carrying was subsequently inhibited across t=3-24 h. In contrast, when we prevented straw from accumulating inside the nest box during the 3 h observation period (by continuously removing it through a hidden door of the nest box), straw carrying persisted across t=3-6 h. These results indicate that the perception of a completed nest is necessary to engage a mechanism that inhibits further straw carrying. However, perceiving a completed nest was not sufficient to inhibit straw carrying behavior, since females whose nest box already contained a completed nest (built by the experimenter at the beginning of the experiment) nevertheless displayed a "bout" of straw carrying lasting approximately 60 min, indicating that the performance of nest building behavior itself might also contribute to its subsequent inhibition.