Lever Pull
Overview
The isometric lever pull task is a precision instrument for measuring forelimb grip force, skilled pulling, and motor learning in rodents. The mouse grasps a force-sensing lever mounted at the front of a behavioral chamber and must generate and sustain a calibrated pulling force to cross a programmable threshold, at which point ConductMaze triggers reward delivery. The force transducer records the entire force trajectory at 500 Hz or above, capturing the shape of each pull attempt — peak force, rate of force development, hold duration, and force variability. Unlike simple grip strength meters that record a single maximal pull, the lever pull task captures the full kinetics of volitional motor output across hundreds of trials per session.
This paradigm is widely used in stroke recovery research, where forelimb reaching and pulling deficits after middle cerebral artery occlusion can be tracked through rehabilitation. It is equally valuable in spinal cord injury models (cervical hemisection), motor neuron disease models (SOD1 transgenic mice), and studies of corticospinal tract plasticity. ConductMaze supports adaptive force threshold training in which the criterion automatically escalates as the animal improves, enabling motor learning curves to be characterized without manual experimenter adjustment. The system also supports bilateral lever configurations for hemispheric lateralization studies following unilateral cortical lesions.
ConductMaze logs each pull attempt with timestamp, peak force, time to peak, hold duration above threshold, and success/failure outcome. The software computes session-level metrics including success rate, mean peak force, coefficient of force variability, force learning curve (peak force across trials), and motor fatigability index (force decline over session duration). Automated shaping protocols can ramp the force threshold from near-zero to target levels over multiple days, reducing experimenter time and improving reproducibility.
Trial Flow
Session Start
House light ON, lever accessible, reward magazine primed
Lever Grasp
Mouse grasps force-sensing lever with forepaw
Force Detection
ConductMaze samples force transducer at 500 Hz, records pull trajectory
Threshold Check
Did peak force exceed programmed threshold for required hold duration?
Reward Delivery
Success tone, reward pellet dispensed into magazine
Failure Feedback
Sub-threshold pull: brief timeout, no reward, trial logged as failure
Inter-Trial Interval
Programmable delay before next trial availability signal
Session End
Max trials or max time reached; export force traces and metrics
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Force Threshold | float | 20.0 | Minimum pulling force in grams required to trigger reward |
| Hold Duration | seconds | 0.5 | Minimum time force must be sustained above threshold for a successful trial |
| Lever Resistance | float | 5.0 | Baseline spring resistance of the lever in grams |
| Max Trial Count | integer | 100 | Maximum number of pull attempts allowed per session |
| Max Session Duration | duration | 1800 | Session time limit in seconds |
| Adaptive Threshold | enum | Off | Automatically increase threshold after N consecutive successes (Off, Staircase, Linear) |
| Inter-Trial Interval | seconds | 5.0 | Delay between end of one trial and availability of the next |
| Sampling Rate | integer | 500 | Force transducer sampling frequency in Hz |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Peak Force | grams | Maximum force generated during each pull attempt |
| Mean Peak Force | grams | Average peak force across all trials in the session |
| Success Rate | % | Percentage of pull attempts that met both force and hold criteria |
| Force Variability | CV% | Coefficient of variation of peak force across trials — lower values indicate more precise control |
| Rate of Force Development | g/s | Mean slope of the rising phase of the force trace from onset to peak |
| Hold Duration Achieved | seconds | Mean time force was sustained above threshold on successful trials |
| Fatigability Index | ratio | Ratio of mean peak force in last quarter vs first quarter of session |
| Trials to Criterion | count | Number of trials to reach 3 consecutive successes at a given threshold |
Sample Data
| Subject | Group | Peak_Force_g | Success_Rate_pct | Force_CV_pct | RFD_g_per_s | Hold_s | Fatigue_Index |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Stroke rehabilitation — tracking forelimb force recovery after MCAo with intensive lever pull training as a rodent analog of constraint-induced movement therapy.
- 2Spinal cord injury — quantifying cervical hemisection deficits in grip force and skilled pulling, with longitudinal assessment during regenerative therapy.
- 3Motor neuron disease — measuring progressive forelimb weakness in SOD1-G93A transgenic mice as a functional endpoint complementing histological motor neuron counts.
- 4Corticospinal plasticity — bilateral lever configuration reveals hemispheric lateralization of motor control after unilateral cortical lesion or optogenetic silencing.
- 5Drug screening — evaluating muscle relaxants, neuromuscular agents, and rehabilitation-enhancing compounds through force threshold dose-response curves.
Related Protocols
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