The balance beam is a narrow ‘walking bridge’ for mice / rats to walk across to test sensorineural balance and coordination. The beam generally sits between two elevated platforms with platforms to hold either mice or rats. Interchangeable beams can be used in thinner and thinner intervals.
The essential components include
- End platform
- (Optional) Start Platform
- (Optional) Encatchment: A soft encatchment to prevent harm on the fall
- Holes (~3mm diameter) along beam center to allow insertion of Protruding pegs
- Tapered Shape
- Second lower flat beam below main beam may be added to assist compromised animals. Detachable. Please inquire if needed.
- Convenient hinges along beam to allow flexible transport.
Prices and Sizes
$ 1490Beam + Stand
- Length: 125cm to 1m available.
- Height: 50cm.
- End box: 20×20 x 20cmcm.
- Width Beam: 6,12, 24, 48mm available.
- (Optional) Start Platform ($300)
- (Optional) Encatchment: ($300)
- (Optional): Adjustable height, Angle (+$150)
$ 1790Beam + Stand
- Length: 125cm to 1m available.
- Height: 60cm
- End box: 25x25x25cm.
- Width of 6,12, 24, 48mm available.
- (Optional) Start Platform + $350 (25cm x 25cm)
- (Optional)Encatchment +$350
- (Optional): Adjustable height, Angle (+$150)
The balance beam is a test of motor coordination and balance in rodents. The test assesses sensorimotor function following motor cortex injury, traumatic brain injury, gamma-aminobutyric acid infusion into the frontal cortex and in rodent models of stroke (reviewed by; Carter et al., 2001). In addition, this test can be used to evaluate the effects of aging and to characterize transgenic animals.
Rodent performance on the beam may improve with time after injury, with the use of drugs and with motor experience (Gentile et al., 1978, Feeney et al., 1982, Brailowsky et al., 1986). Amelioration of motor coordination after injury may be the result of a transient neural loss-of-function in areas remote from but connected to the area of injury.
The balance beam test requires the use of one or more narrow beams with varying dimensions and elevated from the ground. Avoidance stimuli should be used at the start end of the beam. A goal box that serves as escape from the stimuli should be placed at the opposite end. The trials should be video recorded.
Results can be presented as latency to traverse the beam, number of foot slips and mean score if using a grading system (Feeney et al., 1982, Metz et al., 2000).
This test is widely used to assess fine motor deficits. It enables both short and long studies with multiple timepoints. Furthermore, it is inexpensive, methodologically unsophisticated and allows for substantial modifications of equipment and experimental protocol to fit diverse study designs.
Apparatus & Equipment
In the balance beam test, animals are trained to travel across elevated and thin beam(s) to reach an enclosed goal box. Traversing round and thinner beams is harder than square and thicker beams. In general, wooden beams are preferred (Feeney et al., 1982, Carter et al., 2001) Choice of shape and width should take into consideration all variables that may influence motor coordination, including species, strain, age, sex, type of treatment/injury, etc.
Most authors follow the recommendations of Hicks and D’Amato (1975) and Feeney et al. (1982). Behavioral testing should be performed in a sound-proof room with subdued lighting. Use of a start platform is optional. A switch-activated bright light and white noise should be used as avoidance stimuli at the start end of the beam (Feeney et al., 1982, Goldstein and Davis, 1990). Light and noise intensity should decrease gradually along the beam. Elevation of the beam above the ground should not be less than 30 cm (Metz et al., 2000). Beam dimensions can be adjusted, but we highly recommend a minimum length of 1 m to enable division of analysis into segments (see Protocol). Moreover, the beam should be thin enough to present a challenge for the animals and reliably reflect differences in motor coordination. For rats, Metz et al. (2000) used a minimum of 1.2 cm in rectangular beams, whereas Finney et al. (1982) opted for 2.5 cm. For mice, Carter et al. (2001) used a minimum of 0.5 cm in square beams. The beam can have holes (~3 mm diameter) along its center to allow insertion of protruding pegs, if needed. Dimensions of the goal box used by Feeney et al. (1982) – 24.5 by 18 by 20 cm – should be used as a guide for both mice or rats. Dimensions of entrance hole should be adjusted according to species and size/weight of the animals. The box should block light to serve as escape from the bright light. Treats can be placed in the box to further stimulate the animals to cross the beam.
Test should be video recorded. Camera (and tripod) position should enable the full length of the beam to be recorded. If the test is scored by only one observer, we recommend the use of a mirror on the side of the beam opposite to the observer. A soft encatchment can be used under the beam to prevent harm in case of fall. Hinges can be inserted along the beam to facilitate transport.
The balance beam test is used to assess motor coordination and balance in rodents. This test is widely used to characterize the phenotype of transgenic mice, study the effect of motor cortex ablation/lesion (Feeney et al., 1982) or spinal cord injury (Metz et al., 2000), and is therefore useful for pharmacological studies predictive of therapeutic approaches in humans.
Testing should be performed by two investigators to minimize errors in scoring. It is critical that the investigators are blind to experimental conditions. A preliminary study of inter-observer agreement can be performed to improve consistency of criteria (Goldstein and Davis, 1990). All environmental factors should be reduced to a minimum and remain constant throughout the study.
The animals should be given treats in their home cage for a minimum of 2 days before pre-training to reduce neophobia. Habituation to the test room should last 1-2 hours. Before training on the elevated beam, pre-training can be done on a wider plank on top of cushioning to ensure that the test scores accurately reflect differences in motor coordination rather than aversion to walking on unprotected spaces. Alternatively, Carter et al. (2001) recommend using square beams of 1.2 cm and 2.8 cm to train mice and rats, respectively. Gentle guiding or prodding can be done until the animals cross the beam readily.
Duration of training should be determined by the investigator, but it should reflect the minimum number of trials that the control animals need to successfully traverse the beam. Feeney et al (1982) trained rats every other day until no more than two foot slips were observed, which took 10 days. Conversely, Metz (2000) used three footfalls as criterion, whereas Goldstein and Stein (1990) performed 2 training trials. On the other hand, Carter et al. (2001) suggest performing four consecutive trials for three days to generate a stable baseline response.
Light and noise stimuli should remain activated until the animal enters the goal box or up to a minimum of 60 sec (Carter et al., 2001)
As hesitation or pausing on the beam is usually observed when the animal initiates movement or enters the goal box, two lines should be drawn – 10 cm from the beginning and 10 cm from the end of the beam – and performance should be scored within those lines (Carter et al., 2001).
Foot slips in the balance beam test are usually only observed in the hind limbs (Feeney et al., 1982, Goldstein and Davis, 1990, Carter et al., 2001). If two investigators are available, each investigator should score one side of the beam. Animal handling should be performed by the same experimenter at all times to avoid introducing confounding variables.
If performing multiple trials, it is important to avoid tight spacing of timepoints, as Goldstein and Davis (1990) showed that performance of control rats declined in trials spaced by 90 sec. If performing two trials per timepoint, the average should be used for data analysis (Carter et al., 2001). In cases where the animals are not able to successfully traverse the beam, analysis of slips and latency to cross can be divided into segments.
Scoring is based on latency to traverse and number of foot slips. Alternatively, the investigator can use a grading system. In the study of Metz et al. (2000), 0 is given if the animal is completely unable to walk on the beam; 0.5 if it traverses half of the beam, 1 if the whole length of the beam is traversed; 1.5 if the animal reaches the goal box and partially uses the hindlimbs; and 2 if the animal travels across the beam with normal weight support and foot placement. If the study involves brain or spinal cord injury that may compromise motor coordination in one hindpaw, the system reported by Feeney et al. (1982) can be used as it takes into account the animal’s ability to traverse the beam, but also the use (frequency and type of contact with the beam) of the affected hindpaw. Control animals should always score maximum points in any grading system.
At the end of each trial, the animal should be placed in its home cage. The apparatus should be wiped after each trial and thoroughly cleaned with 70% ethanol at the end of the day.
Popular modifications of experimental protocol are related to which species (mouse or rat) and what is being tested (phenotype of transgenic animals, effect of injury and/or efficacy of drug). Spacing of timepoints and length of study are of particular importance if evaluating progression of motor coordination after injury or administration of drug.
Besides changes in elevation from the ground (Goldstein and Davis, 1990, Metz et al., 2000, Carter et al., 2001, Curzon et al., 2009) and beam length and/or width (Feeney et al., 1982, Metz et al., 2000, Carter et al., 2001, Curzon et al., 2009), beams of differential width and/or shape (Metz et al., 2000, Carter et al., 2001) have been used for fine-tuned characterization and detection of subtle motor deficits.
If testing animals that show compromised motor coordination, a detachable second flat beam positioned below the main beam may be added for assistance. Also, using an inclined beam may help the animal’s performance, as mice show a tendency to run upwards to escape (Brooks and Dunnett, 2009).
The data obtained from the balance beam test can be shown by plotting the latency to traverse the beam (A), number of foot slips (B) and score on a grading system (C). Depending on study design, data can be shown as results on a single test day (A) or as timecourse (B and C, typically used to report effects of injury and/or administration of drugs). All following graph samples are mean ± standard error of the mean:
This simple way of presenting results allows for easy visualization of potential motor deficits induced by genotype, age, injury, drug administration, etc.
Strengths & Limitations
The balance beam test is a reliable, inexpensive and methodologically unsophisticated method of assessing motor coordination that enables both short and long studies, and assessing effects of central nervous system injury and treatment with drugs. This test can be more sensitive than the rotarod for detection of fine motor deficits (Curzon et al., 2009).
The balance beam test may not be well suited for animals that display decreased activity. On the other hand, the cognitive requirements associated with reaching the goal box demand care with potential confounding of results. Overtraining animals may induce decreased willingness to walk on the beam (Luong et al., 2011).
Summary & Key Points
- The beam balance test is a well-established method of assessing motor coordination and balance in rodents.
- This test is used to assess fine deficits related to sensorimotor function in both intact animals (e.g. to characterize a genotype or evaluate the effects of aging) and animals subjected to surgical procedure (e.g. motor cortex or spinal cord injury).
- The animal is required to travel across the beam from a starting point with light and noise avoidance stimuli to a goal (escape) box.
- The balance beam test enables automated recording and adaptation of equipment and protocol to fit study specificities.
- Motor coordination is primarily evaluated by latency to traverse the beam and number of foot slips. The use of a consistent grading system further contributes to differentiate groups based on their performance on the beam.
Curzon P, Zhang M, Radek RJ, Fox GB (2009) The Behavioral Assessment of Sensorimotor Processes in the Mouse: Acoustic Startle, Sensory Gating, Locomotor Activity, Rotarod, and Beam Walking. In: Methods of Behavior Analysis in Neuroscience (Buccafusco, J. J., ed) Boca Raton (FL).