Tether Management & Headstage Counterweight#
Incorporating elastic thread into the commutator setup can better approximate freely-moving animal behavior by:
Preventing the tether from entering the animal’s field while it explores the arena
Counterweight-ing the headstage
This is accomplished by catching one end of the thread on the commutator’s gear hook and attaching it to the tether at multiple evenly-spaced points using Kapton tape. More details and diagrams are provided below.
Commutator Mounting Location#
Mount the commutator as high as possible. This minimizes the variation in tension magnitude and direction as the animal traverses the arena, and minimizes lateral tension. As a rule of thumb, try to not exceed ±25° deviation from the nominal 0° position for a total 50° range. Refer to the diagrams below and to the right for reference.
The angle θ exceeds the ±25° rule-of-thumb provided above. It’s about 40° in this diagram.#
The angle θ satisfies the ±25° rule-of-thumb provided above. It’s about 20° in this diagram.#
Elastic Thread Length#
The elastic thread’s length should be tuned so that it properly counterbalances the weight of the headstage. Below is a procedure for this:
Unwind enough thread from the spool to be able to extend it from the commutator to the closest point in the experimental field.
Make a loop at the end of the thread and catch the end of the thread on the commutator gear hook, or tie the thread around the commutator hook.
Pinch the thread somewhere close to the spool, and bring it to the center of your arena. The goal now is to feel tension that has similar magnitude of the weight of the headstage you intend to use. Move the thread lower or higher along your pinching fingers depending on whether you want to decrease or increase tension. Proceed from this step once you find the sweet spot.
While pinching the thread in the same spot, move your hand to the furthest extent from the commutator in the behavioral arena. The tension should feel similar to the previous step. This is important so the animal does not start to feel lifted while it explores this area of the arena.
Cut the thread where you are pinching it. This is where you will tack furthest point of the tether to the with Kapton tape.
Tip
Clover 3158 elastic thread has successfully been used for the purpose described on this page.
