Modified Forced Swim Test

The modified forced swim test (mFST), developed by Cryan, Markou, and Lucki (2002), extends the classic Porsolt FST by introducing a structured two-day protocol with distinct behavioral scoring that separates active coping strategies. On day 1, rats undergo a 15-minute pre-exposure swim that induces learned helplessness through the experience of inescapable stress. On day 2, a 5-minute test session is scored for three mutually exclusive behaviors: immobility, swimming, and climbing. This temporal separation and refined ethogram engage overlapping but dissociable neural circuits — swimming behavior maps onto serotonergic transmission via the dorsal raphe to prefrontal cortex pathway, while climbing behavior reflects noradrenergic activity originating in the locus coeruleus.

The critical advance of the mFST over the original Porsolt version is pharmacological specificity. Selective serotonin reuptake inhibitors (SSRIs like fluoxetine) selectively increase swimming time without affecting climbing, while norepinephrine reuptake inhibitors (NRIs like desipramine and reboxetine) selectively increase climbing without affecting swimming. Dual-action antidepressants increase both behaviors. Immobility decreases in all effective antidepressant conditions. Behavior is scored in 5-second bins across the full 5-minute test, and the predominant behavior in each bin is recorded, yielding 60 bins per session.

ConductMaze automates the mFST with dual-camera posture analysis (overhead for swimming trajectory, side-view for climbing classification) and applies machine-learning classifiers trained on expert-scored reference datasets. The software enforces the 24-hour inter-session interval, manages cohort scheduling across treatment groups, and generates pharmacological profile plots that directly compare swimming and climbing ratios. Bin-by-bin temporal heatmaps reveal the time course of behavioral transitions within each session.