Introduction

The Parallel Beam Task is used to measure motor function in rodents. It allows the assessment of different motor function parameters such as postural balance, angular limb rotation, weight support, and limb coordination for measuring not only subtle but also severe motor deficiencies in rodents. The Parallel Beam Task, like several behavioral tests such as the Rotarod and the Balance Beam, can be used to test the effect of neurodegenerative diseases and spinal cord injury on the motor function of rodents (Shiotsuki et al., 2010). 

The Parallel Beam Task consists of two horizontal, parallel flat metal beams with a 3.5 cm space between them. At one end of the beams, a neutral start platform is present while the subject’s home cage is present at the other end to serve as a refuge. During the task, the subject is required to walk across the beams from the starting platform to the home cage without making any stops. The beams are framed by high acrylic sidewalls that prevent the subject from turning back. The task makes use of food reward rather than aversive motivation, which is less stressful for the subject. The Parallel Beam Task not only allows a quantitative assessment of motor performance but also allows a qualitative assessment thorough evaluation of the subject’s balance and coordination during the task. 

Other apparatuses used to assess motor performances in rodents include Gait Test, the Triple Horizontal Bars, and the Static Rods Test.

Apparatus and Equipment

The Parallel Beam Task consists of two horizontal, parallel flat metal beams with a 3.5 cm space between them. The beams measure 100 cm in length and 1 cm in width and are elevated at 30 cm above the ground. The apparatus is framed by acrylic sidewalls measuring 19 cm in height, and are spaced 9 cm apart. At one end of the beam, a neutral starting platform is present while the subject’s home cage is present at the other end. Under the walking platform, a mirror of the same length of the platform is positioned at an angle of 45°.

Training Protocol

Clean the apparatus before and after trials to prevent the influence of olfactory cues from previous trials. A tracking and recording system such as the Noldus EthoVision XT system can be used to assist with observations. 

Habituation and Pre-training

Place the subject on the starting platform. Allow the subject to walk on the platform and habituate with the environment. Conduct habituation sessions a day before testing. 

Parallel Beam Task

Place a food reward at the entrance of the home cage. Place the subject on the starting platform. Allow the subject to walk from the starting platform to the home cage. Conduct trials until the subject successfully crosses the parallel beams without stopping for five trials.

Literature Review

Investigation of motor performances in rats using the Parallel Beam Task 

Ficiur, Faraji, and Metz (2018) used the Parallel Beam Task for qualitative assessment of motor performance in rats with cerebral ischemia. Twenty-three male Long Evans rats that were three months old were used in the study. Twelve rats received motor cortex devascularization, whereas the remaining 11 rats served as non-lesion control subjects. In the cortical lesion subjects, unilateral lesions were induced on the left hemisphere for six subjects and the right hemisphere for the other six subjects.  During the task, banana-flavored food pellets were placed at the home cage end to serve as motivation. Trials were conducted until the subject walked from the starting platform to the home cage without making stops for five successive trials. The qualitative analysis included videotape inspection of each of the subject’s four limbs during task performance using lateral and ventral views. Four parameters of the subject’s walking pattern were recorded: 1) limb rotation angle when placed on the beam; 2) position of the limb in reference to the beam surface; 3) the average number of placing attempts per step, and 4) the number of foot slips per step. In the limb rotation angle, the results indicated that the subjects with the cortical lesions produced significant contralateral limb angular placement deficits in both fore and hind limbs. In addition, the subjects with the cortical lesions also showed greater limb placement deficits in contralateral limbs in reference to the beam surface. In the number of placing attempts per step, contralateral forelimbs had a greater number of placing attempts as compared to ipsilateral or control limbs. Observation of the number of foot slips per step indicated that although foot slips in any limbs were rare, it mostly occurred in contralateral limbs than ipsilateral or control limbs.

Data Analysis

The following can be observed using the Parallel Beam Task,

• Time taken to complete a trial
• Number of times the subject made stops while walking on the platform
• Limb rotation angle
• Limb placement position
• Total number of foot placing attempts
• Total number of foot slips

Strengths and Limitations

Strengths

The Parallel Beam Task can be used to evaluate motor performances in rodents. It allows a quantitative as well as a qualitative assessment of motor performance for more accurate results. The task utilizes food rewards as motivation rather than aversive stimuli that elicit stress in the subjects. Training the subjects on the apparatus takes a short amount of time. The Parallel Beam Task can be used as a translational tool to test the effects of spinal cord injury, stroke, and neurodegenerative diseases on motor function. In addition, the Parallel Beam Task can also be used to ensure proper motor functioning of rodents for other behavioral assays that require proper motor coordination for task performance.

Limitations

Overtraining and improper handling of subjects may affect task performance. Unintentional stimuli may interfere with the way the subjects perform the task. Factors such as age, gender, and strain of the subject may affect task performance.

Summary

• The Parallel Beam Task is used to measure motor function in rodents.
• The Parallel Beam Task consists of two horizontal, parallel flat metal beams that are spaced 3.5 cm from each other. It is framed by acrylic sidewalls that prevent the subjects from turning back when walking on the beams. 
• It can be used to measure the effect of neurodegenerative diseases, spinal cord injury, and stroke on the motor function of rodents.

References

1. Ficiur, B., Faraji, J., & Metz, G. A. (2018). Use of the parallel beam task for skilled walking in a rat model of cerebral ischemia: A qualitative approach. Learning and Motivation, 61, 74-84. doi:doi.org/10.1016/j.lmot.2016.12.002.
2. Shiotsuki, H., Yoshimi, K., Shimo, Y., Funayama, M., Takamatsu, Y., Ikeda, K., Takahashi, R., Kitazawa, S., & Hattori, N. (2010). A rotarod test for evaluation of motor skill learning. Journal of neuroscience methods, 189(2), 180–185. https://doi.org/10.1016/j.jneumeth.2010.03.026