FRAME: A frame was modified to be more efficient than what was constructed in 2022; the unit continues to function as a module that integrated with the existing system without permanently altering the system’s structure or component capability. This frame functions like a universal joint having two independent axes of rotation. We selected commercially-available aluminum t-channel to build the frame, as this material is easy to machine and adapt for our application. In other words, the frame acts like a gyroscope.
POWER SUPPLY: The Power supply () connects the wall outlet to two motors.
CONTROLLED MOTION: The DigiGait has 2 degrees of freedom, pitch and roll. In both directions (clockwise and counterclockwise, defined as forward and backwards), the motors can be moved by being given power. The power given directly corresponds to the force applied by the motor; this power is variable. More power can be provided to make the motor move more quickly. It is advantageous to gradually increase and decrease the power of the motors as it increases movement accuracy. Currently, the motors are given a gradual acceleration and deceleration period, and do not hold a constant velocity for any substantial time. This is not a limitation; a constant velocity can be held if desired. The rate of acceleration, as well as the duration of the periods, can be changed. Note that upon reaching any destination, the DigiGait takes some time to settle. This time is at a max of 5 seconds by default, but can be reduced substantially with slower speeds, or potentially increased with higher speeds.
The DigiGait is capable of simple and complex movement commands. The most basic command often utilized is "There and Back". An example use of this command is to roll the DigiGait 5 degrees and then bring it back 5 degrees. It is possible to vary the speed of this movement, as well as the distance traveled. It is also possible to add a pause at the target destination. Note that increasing the speed of the movement can result in decreased precision, while reducing the speed can increase precision. Tolerance is set at 1 degree by default, but can be reduced with slower movements. The accelerometer measures the movement and returns a value within 0.3 degrees of the actual positions.
A complex command, "Return to Zero", allows the DigiGait to return from any position to zero, within 0.5 degrees by default. This involves a series of gradual movements stepping towards zero. The speed of the command can be changed to adjust the tolerance; increasing the duration of command will lower the tolerance to as low as 0.3 degrees, which is the tolerance of the accelerometer.
Another complex command, "Shake", allows the DigiGait to rapidly move back and forth on either axis. It is possible to change how quickly this occurs, for how long it occurs, the direction this occurs in, and more. An example of this command is to shake in the pitch direction, varying position between 0 and 3.0 degrees, and taking 1 second to move between both ends of the range. Note that the shake command does possess an amount of uncontrollability associated with the settling of the DigiGait; uncontrollable does not mean unpredictable or unmeasurable, this simply means that we are relying on the settling of the DigiGait to contribute to the command.
RODENT STUDIES: The pilot study of twelve male mice included include both hind limb unloaded (HU) and full weight-bearing GROUND controls. Gait assessment of each mouse was be performed prior to HU or before the start of the study as a GROUND control, and then again after 14 days. From these mice we determined if: i] the system is functional and we can modify the design if necessary, and ii] the system can reliably measure gait data across a range of speeds and displacements
METRICS ASSESSMENT
1. General: We had originally planned to use 20º displacements as the baseline metric. However, when moving on the treadmill, displacements of this magnitude, even at relatively low speeds, can result in mice being pushed laterally and forward into the enclosure. Thus, displacements of 5º appear optimal for this sex and strain.
2. Speed: When the speed of the treadmill gets below ~12 cm/s, the rodents can essentially “ride” the displacement in the lateral direction. It remains useful for a forward pitch in terms of identifying if braking gait responses are altered. The utility in the lateral direction (roll) would be to identify if stability is altered by some stimulus (e.g., Radiation).
17.5 cm/s appears to be an optimal speed to promote forward locomotion and recovery with perturbations. Faster speeds and this strain of mouse runs to the back of the encasement.
3. Pitch: Forward pitch appears to provide a good metric of the ability to brake and remain in motion – both if the motion is continuous (without pause after forward pitch) and when a pause at a downward angle is provided. Time to return to linear locomotion is also a valued metric and is affected by treatment.
4. Roll: Rolling metrics (with and without pause) likewise appear to reflect stability, with important metrics including stance width and paw angle variability, with time to recovery of linear locomotion serving as a putative important metric regarding effects of treatments.
5. Pauses for both pitch and role: Pausing in the midst of motion (e.g., at 5 º) of roll or pitch permits the assessment of 2 “recoveries” – first from the initial perturbation (with associated gait pattern changes reflective of neuromotor and sensorimotor deficits) and then a timing of return to normal locomotion, if possible, and then with a return to baseline position, another set of recoveries.
6. Shaking: The shaking feature appears very useful in measuring gait pattern metrics associated with stability, and also a return to normal locomotor behavior upon cessation. We feel that for shaking especially, measuring gait parmaters prior to, during, and after the shaking challenge (and then comparison with baseline (“pre”) measures are of particular importance).
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