A tube-restriction test: A candidate impulsivity-related assay based on nose-poke behavior dynamics

Impulsivity is a multidimensional endophenotype, yet current rodent assays require prolonged training, dietary restriction, or yield binary outcomes.

We developed the tube-restriction test (TRT) as a complementary assay to exploit innate approach-avoidance conflict. Spontaneous nose-poke behavior was video-recorded and analyzed via an unsupervised principal component analysis-Gaussian mixture model pipeline. The core metric IBTP (impulsive burst time percentage) indexes the propensity for temporally clustered nose-poke bursts, complemented by ST-CV (state-transition coefficient of variation), which quantifies the temporal irregularity of transitions between burst and non-burst states. Three supplementary parameters further characterize inhibitory capacity: first nose-poke latency (FNL), maximum safe stay duration (MSSD), and inhibition-impulse balance index (IIBI).

In 30 male ICR mice, the TRT demonstrated moderate test-retest reliability over a 14-day interval (IBTP: ICC = 0.64; ST-CV: ICC = 0.52). Criterion validity was supported by significant correlations between IBTP and home-cage aggression (ρ = 0.56) and acoustic startle habituation rate (ρ = 0.47), whereas ST-CV correlated negatively with both (ρ = -0.59 and -0.39, respectively). Discriminant validity was indicated by non-significant correlations with anxiety-like behavior; a marginal trend was observed between IBTP and locomotor activity (ρ = 0.36, p = 0.054).

The TRT requires no pre-training or dietary restriction, providing continuous, multidimensional quantification with sub-second resolution.

The TRT offers a rapid, training-free candidate assay for impulsivity-related phenotyping in rodents, though convergent validation against established operant benchmarks is required to confirm specificity for impulsivity rather than related constructs such as exploratory drive.