Immobility Time
Total duration of immobility (absence of escape-oriented movement)
ConductVision · Behavioral Analysis
Tail Suspension Test
Measure depression-like immobility and behavioral despair in mice.
MouseDepressionAuto Export
ConductVision / Tail Suspension Test
Recording / Trial 3subject tracked
Immobility62%
Latency to Immobility48s
Struggle Bouts15
Key Parameters
Metrics automatically extracted by ConductVision.
Immobility Latency
Time from suspension onset to first immobility episode
Struggle Bouts
Number of active escape attempts during the session
Struggle Intensity
Movement amplitude and energy expenditure during active phases
Curling Episodes
Frequency of tail-climbing behavior (C57BL/6 confound detection)
Temporal Bin Analysis
Immobility progression across 1-minute intervals over the 6-minute test
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Power Spectrum
Frequency analysis of movement — high-frequency struggles vs low-frequency swaying
Swing Episodes
Pendulum-like lateral swaying — passive movement distinct from active struggle
Mean Bout Duration
Average length of individual immobility episodes
Struggle-to-Immobility Transitions
Number of switches between active and passive states
Last 4 Minutes Immobility
Immobility in final 4 min — most sensitive antidepressant window
Vigor Index
Composite of struggle frequency, intensity, and duration
What is the Tail Suspension Test?
The Tail Suspension Test (TST) is a widely used assay for depression-like behavior in mice. Animals are suspended by the tail and alternate between active struggling and immobility. Increased immobility reflects behavioral despair, which is reduced by clinically effective antidepressants — making TST a standard pharmacological screen.
ConductVision automates immobility scoring through video-based movement detection, eliminating observer bias. The software distinguishes true immobility from subtle swaying, detects confounding tail-climbing in susceptible strains (e.g., C57BL/6), and provides temporal analysis of immobility progression across the test session.
Protocol Parameters
| Parameter | Description | Default |
|---|---|---|
| Suspension Height | Distance from tail-attachment to floor | 50 cm |
| Tape Placement | Adhesive tape position on the tail | 1 cm from tip |
| Test Duration | Standard session length | 6 min |
| Immobility Threshold | Movement below threshold scored as immobile | < 5% pixel change |
| Number of Subjects | Animals tested simultaneously | 1–4 (partitioned) |
| Partition Walls | Visual isolation between adjacent subjects | Opaque dividers |
| Tail-Climbing Prevention | Device to prevent C57BL/6 curling confound | Plastic cylinder on tail |
| Drug Pre-Treatment | Standard antidepressant administration window | 30–60 min before test |
| Scoring Window | Most sensitive portion for antidepressant detection | Last 4 min of 6 min |
Interpreting Results
↓
Decreased Immobility Time
Antidepressant-like effect — reduced immobility is the primary readout, seen with SSRIs (fluoxetine 20 mg/kg), SNRIs, TCAs, and ketamine.
↑
Increased Immobility Time
Pro-depressive or learned helplessness state — elevated after chronic unpredictable stress or corticosterone administration.
↓
Shortened Immobility Latency
Rapid onset of despair — faster transition to immobility suggests heightened susceptibility to behavioral despair.
↑
Increased Struggle Intensity
Enhanced active coping — noradrenergic antidepressants (desipramine, reboxetine) preferentially increase struggle vigor.
↑
Excessive Curling
Confound — tail-climbing in C57BL/6 strains artificially reduces immobility scores; must be detected and excluded.
↓
Flattened Temporal Progression
Loss of normal immobility increase over time — stimulants may reduce immobility through motor activation rather than antidepressant action.
Research Applications
Antidepressant Screening
- SSRI validation — fluoxetine, sertraline, paroxetine dose-response curves
- Novel antidepressants — ketamine, psilocybin, and NMDA modulators rapid-acting screening
- TCA and SNRI profiling — imipramine, venlafaxine with struggle type classification
Depression Models
- Chronic stress — CUMS and social defeat effects on TST immobility
- Genetic susceptibility — strain differences (BALB/c high immobility vs Swiss low)
- Serotonin transporter — 5-HTT knockout and overexpression despair phenotyping
Mechanism & Pathway
- Monoamine dissection — selective NE vs 5-HT reuptake inhibitor struggle type differences
- BDNF signaling — BDNF Val66Met knock-in and TrkB modulator effects on despair
- Inflammatory pathways — LPS-induced sickness behavior vs true depressive-like immobility
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