Motor Tests

Motor function, among other abilities such as communication, contribute heavily to the quality of life of an individual. The coordination of precise movements in order to perform an intended action, such as walking or writing, is managed by the motor system. The functioning of this system is based on the cooperation of the central nervous system, the musculoskeletal system, as well as the sensory system.

Development of motor skills follows three distinct principles; cephalocaudal, proximal-distal, and general to specific, as observed by Dr. Arnold Gesell. Gesell’s principle of development direction suggests that motor development begins in an orderly fashion from head to toe and closest to the body to the farthest part (Salkind, 2004). As the control over these parts is improved upon, an individual begins to develop finer movement skills.

Motor skills are categorized as,

• Gross Motor Skills: These skills involve large muscle groups and are acquired as part of childhood motor learning. The skills can be further divided into locomotor skills and object control skills.
• Fine Motor Skills: These skills involve the smaller muscles, including hands and face, to control smaller movements. Fine motor skills are acquired following the development of gross motor skills. Further, unlike gross motor skills that are retained even after a period of no-use, fine motor skills may not be retained if not used.

The quantitative and qualitative changes in motor skills are dependent on the maturation of the central nervous system and the muscular system. Motor learning progresses through three stages: the cognitive phase, the associative phase, and the autonomous phase. The progression of motor learning can be understood through Thorndike’s (empirical) Law of Effect. A positive association between motor skill and the outcome results in the promotion of learning of the skill (Adams, 1971). As the positive association grows stronger, robust neuronal modifications occur (Dayan, & Cohen, 2011; Kapogiannis, Campion, Grafman, & Wassermann, 2008). However, it is simply not just the feedback of an action that influences motor learning. Other factors such as physical health, genetic factors and mental health among others, can also contribute to the rate of motor development (Ferguson, Cassells, MacAllister, & Evans, 2013; Golding, Emmett, Iles-Caven, Steer, & Lingam, 2013). On the whole, though motor development does not depend on age and experience, it is, to a great extent, influenced by them (Salkind, 2004).

Delay in acquiring of these skills or impairments can be markers of diseases and disorders such as Autism Spectrum Disorder (McPhillips, Finlay, Bejerot, & Hanley, 2014) and Parkinson’s disease (Opara, Małecki, Małecka, & Socha, 2017). Partial or complete loss of motor function may also be a result of injuries to the musculoskeletal system or nervous system. Apart from these causes, deficits in the sensory system can also exhibit themselves as motor control impairments.

2.1 Gait Assays

Despite the differences in the gait of humans and animals, animal-based gait research provides significant insights into the motor impairments resulting from diseases, disorders, and injuries. Gait assessments allow observation of gait abnormalities, which are evaluated using parameters such as stride length, velocity, stance, and footprint area.

Gait Test

The Gait Test has undergone many transformations over the years. The apparatus is delightfully simple in design and effective enough to allow observation of gait abnormalities. The apparatus consists of a linear track lined with paper that leads to an enclosed box. The animals are placed on the track after their paws are dipped in ink or paint. The animals are motivated by the enclosed box to cross the track, which thus allows observation of their locomotion and footprints.

fTIR Walkway

The fTIR Walkway was designed as a more sophisticated approach to gait testing (Mendes et al., 2015). In comparison to the traditional method, the fTIR Walkway incorporates automated analysis of animal’s gait using a non-invasive optical touch sensor and high-speed imaging. This apparatus, in addition to recording the standard parameters of gait analysis, also allows recording of a range of other kinematic parameters associated with locomotion.

Treadmill

Though often used as an exercise system, the Treadmill can also be used to observe gait patterns in rodents at varying speeds and inclines. The apparatus comes as a multilane treadmill, with shock grids at the start that can be used to motivate the subjects.

2.2 Balance Assay

Deficits in the visual system, vestibular system, and proprioception are often associated with loss in balance. In animal research, where a wide range of behavioral assessments relies on locomotion, loss of balance may present itself as cognitive dysfunction. Balance assays, thus, are used as a pre-assessment tool to eliminate the possibility of motor dysfunctions. These assays also provide insights into motor impairments resulting from injuries, neurodegenerative diseases, and aging. Balance assays often take advantage of the animal’s fear of falling to motivate them to complete the task. Parameters usually recorded in these assays include time taken to complete the task or remain on the apparatus and number of falls.

Balance Beam

The Balance Beam has a simple design the usually includes a circular rod placed at a height from the ground. The simplicity of the apparatus allows the use of different combinations of rod thickness and shapes in addition to inclusions of start and end boxes. Experimenters have the option to include an enclosed box at the end to encourage the subjects to cross the rod.

Rotarod

The Rotarod is a motorized cylinder on which the subjects are placed to evaluate their balance as well as motor coordination. The apparatus permits varying levels of acceleration in a fashion similar to the Treadmill. An automated timer and infrared sensors assist with performance evaluations.

Geotaxis Test

The apparatus is available in metal and acrylic construction. The Geotaxis apparatus consists of a grid/high-friction inclinable plane that allows the assessment of vestibular sensitivity. The ability to incline the plane to different angles allows control over the task difficulty. (See also Tilt Ladder).

2.3 Grip Strength and Mechanical Loading Assay

Neuromuscular function and muscular strength are assessed in the grip strength assays. Assessment of this ability provides insights into the decline of muscle function as a result of neurodegenerative disorders and neuromuscular diseases. In the aging population, a decline in grip strength often has a significant impact on the quality of life. Parameters often recorded in these assays can include duration on the apparatus, load-bearing, and falls or slips.

Grip Strength

The apparatus consists of a grid that is attached to a force sensor. The subject is gently lifted by its tail such that it grips the grid with its forepaws. Assessment of grip strength is done by gently pulling the subject backward by its tail until it releases the grid.

Incline Rolling Ladder

The Incline Rolling Ladder is usually used in the assessment of functional deficits arising from motor impairments. The general task involves the subject climbing up the apparatus that consists of adjustable rungs that are made of half-smooth and mobile surface, and half textured and immobile surface. The subject’s ability to differentiate between the texture and grip strength plays a crucial role in the completion of the task.

Grid Test

The Grid Test essentially tests the ability of the subject to hang on the mesh. The apparatus consists of a metal mesh that is raised to a height from the ground. The animal is lifted by its tail and placed in the center of the mesh until it grips on to it with all four paws. The apparatus is then inverted, and the fall is timed. The apparatus is also available in two other variants, Horizontal Grid, and Vertical Grid.

Stairway Test

The apparatus includes a vertical rising stairway made of thin cylindrical rungs. The apparatus was first introduced by Boltze et al. (2006) to evaluate sensomotoric stroke deficits in rats. While the fear of falling is a motivation in this triangular stairway, the main motivating stimulus is the presence of the home-cage at the top of the ladder. However, this home-cage is not visible during the task, and its presence is learned during the task sessions.

Climbing Tower

The Climbing Tower is often used as a resistance exercise to assess the effects of mechanical loading. The apparatus consists of a tall cylindrical mesh tower with water bottles placed at the top. The subjects are allowed to climb up the tower to obtain the water reward voluntarily.

2.4 Motor Coordination Assay

Motor coordination involves the combination of kinematic and kinetic components in order to perform an action. Deficits in these abilities are seen in disorders such as Autism Spectrum Disorder (Fournier, Hass, Naik, Lodha, & Cauraugh, 2010) and are also related with aging (Seidler et al., 2010). Further, much like balance, impairments in motor coordination can also impact performances of animals in other behavioral tests such as the Morris Water Maze. Parameters observed in these assays can include orientation time, functional paw placement, and transit time.

Horizontal Ladder

The Horizontal Ladder was designed by Metz and Whishaw (2002) to evaluate skilled walking in cortical and subcortical lesioned rats. The apparatus consists of a horizontal path with removable rungs that allow adjustment of the spaces between them. The ladder can be clamped down to basins, which can be used to add an aversive or non-aversive motivation to the task.  Additionally, the path width is such that it prevents the animal from turning around in the track.

Static Rod Test

The Static Rod test involves subjects walking on a circular rod clamped on one end, with the other end extending into space. The trials begin with the widest rod followed by subsequent narrower rods until the subject fails to turn from the suspended edge and reach the clamped end. Similar apparatuses include the Triple Horizontal Bars and Parallel Bars.

Parallel Rod Floor Test

Unlike other apparatuses, the Parallel Rod Floor Test does not force the subjects to move. The apparatus allows reliable assessment of ataxia. The floor consists of parallel metal rods, and the subject is contained within this arena using a clear acrylic box.

2.5 Dexterity Assay

Dexterous movement capacity may be limited in individuals with neurodegenerative diseases and disorders such as arthritis and Parkinson’s disease. Congestive heart failure, repetitive stress injury, and congenital disorder, among other diseases and disorders, can also affect dexterity.

Skilled Forelimb Test

The apparatus is popular in the assessment of skilled reaching. The automated device tasks the animals to pull the handle through a slot in the device walls until a predefined force threshold is reached in order to obtain a food reward.

Pawedness Trait Test

The Pawedness Trait Test apparatus allows the observation of the degree of pawedness in rodents. The apparatus consists of a mesh cylinder placed within an open field. The animal is tasked with obtaining the food reward placed behind the mesh. This mesh design enables observation of intermediate movements required to obtain the reward.

2.6 Locomotion and Ambulation Assay

Impairments of locomotor activity often is a result of the loss of motor functions caused by diseases or injuries. Studies involving the generalized observation of movements in organisms can be observed in open arenas or even mazes that are often used in learning and memory tasks such as the T-Maze and the Radial Arm Maze. The use of a tracking and recording system such as the Noldus EthoVision XT assists with the observation of behaviors.

Open Field

The Open Field test was developed by Hall and Ballachey (1932) and is used in a wide variety of tests involving exploratory behaviors. The apparatus consists of an open arena contained by high walls to prevent the animal from escaping the arena. The apparatus is available in different combinations of clear and opaque walls and the number of arenas in an apparatus to allow observation of multiple animals.

SmartCage System

The SmartCage System offers observation a range of behavioral activities, including active/inactive locomotion and rearing. The automated system makes observation and recording of behavioral data easy.

Drosophila Shallow Chamber

The Drosophila Shallow Chamber was designed by Simon and Dickinson (Simon, & Dickinson, 2010) to create a shallow volume of space that allows the flies to move in a single layer. This design makes the observation of locomotion of flies easier to record and analyze.

Assessment of human motor development and functions involves evaluation of motor control and motor learning. These assessments more often, than not, are based on rating the observed performances of the individual as they perform a task or movement (For digital healthcare tools, visit Qolty). With advancements in virtual reality systems (For virtual reality tools visit Simian  Labs), many evaluations are now taking advantage of the immersive nature of virtual environments, to evaluate motor functions as well as observe underlying brain processes (Decety, & Jeannerod, 1995).

The most prominent use of virtual reality can be seen in rehabilitation treatments (Massetti et al., 2018; Yanovich, & Ronen, 2015). Another growing area of virtual reality is in exergaming, which is exercising via virtual reality (Cacciata et al., 2019; Ye, Lee, Stodden, & Gao, 2018). The rising popularity of virtual reality in motor function rehabilitation and exercising is primarily due to the opportunity to create tailored environments that meet the comfort level of the participants. Further, the control that can be exercised over the environment reduces the anxiety associated with training in a real-world set-up. Immersive realities further the acceptability of virtual applications and treatments due to the sense of presence that they promote. (For human virtual reality experiments, click here)

The following are a few suggestions to perform experiments in an ethical manner

• Animals should be habituated to handling to minimize the effects of handling stress.
• Animal testing following injury or other pain-inducing treatment should ensure that pain is minimized to an acceptable level for the research.
• Cushion floor or other measures should be taken in a task that involves falls to prevent injury to the animals.
• Overtraining of the animals can result in decreased motivation to perform the task and muscle fatigue. Hence, appropriate rest intervals or task durations should be maintained.

Apart from the above guidelines, efforts should be made to ensure the overall wellbeing of the animals in the laboratory. Animals should not be subjected to unnecessary stress or mishandling at any time.

Further to gain the most from the experiments, apparatuses should be cleaned as necessary to prevent any lingering olfactory cue from influencing the subject behavior. The type of illumination used may also affect the performances. Hence appropriate lighting arrangements should be made.

In human experiments and research, the following are a few guidelines that should be followed

• Explicit consent of the participants should be obtained prior to testing.
• Experiments should be age-appropriate and take into consideration all medical factors.
• Safety and well-being of the participants should be prioritized above all.
• Experiments that involve potential triggering set-ups should be carefully created so as not to overwhelm or stress the participant.
• Appropriate measures should be taken when using virtual reality for experimentation.

Motor skills develop with age and experiences of an individual, possibly based on reward-related learning of those skills. Impairments in motor development and motor function significantly affect the quality of life by decreasing the independence of an individual. Neurological and musculoskeletal disorders and diseases cause motor impairments by disrupting the cooperation between different systems involved in motor function. Apart from diseases and disorders, aging and injuries can also result in poor motor functioning.

Virtual reality-based approaches are now opening new fronts of human-based motor functioning research. Primarily, virtual reality is growing as a complementary treatment to traditional rehabilitation treatments. However, the assessment of human motor development and functioning are still limited to non-invasive observations in humans. Given the ethical concerns with human-based research, motor impairments are evaluated using animal models. Animal models improve the understanding of diminished motor functions associated with diseases and disorders despite the differences in functionality. They also provide a practical approach to drug testing and development.

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