Subject Tracker Headband
Developed with and written by Dustin Martin
As detailed in the description of our calibration frame, the accuracy of the Brainsight 2 neuronavigation system used in our lab depends not only on the calibration of a tracker on the TMS coil, but also on proper and consistent calibration of the tracker worn by the research subject. Calibration of this tracker (“registration”) occurs by locating at least three fiducial markers on the head. Because these markers are part of the subject’s anatomy, their consistency is not an issue; however, the tracker used to register the subject to the neuronavigation system is held in place on the subject’s head by an elastic strap or a set of glasses. The elastic strap slides easily on the hair; the glasses, depending on the shape of the subject’s face, tend to slide off the nose. Such movement of the subject tracker can dramatically affect the precision of the coil’s placement during an experiment.
To improve the stability the of the subject tracker we modified the elastic headband so that it can be easily attached to a plastic headband (which can be purchased at any drugstore). Strips of hook-and-loop fasteners on both the elastic and the plastic headbands attach the two pieces; this allows different size plastic headbands to be substituted to accommodate subjects with different size heads. The subject places the plastic headband over the head such that it fits behind the ears, as in normal use, while the elastic portion secures underneath the subject’s chin, like the strap for a bicycle helmet. The plastic headband grips the subject’s hair and provides additional points of stability by extending behind the ears, while the elastic strap provides a third point underneath the chin. These improvements greatly limit subject tracker movement during a session.
1. Strips of hook-and-loop fastener were cut and attached to the top portion of the plastic headband using their adhesive backing. The elastic band is attached to the other side of the fasteners, such that the collar for the tracker is approximately centered on the headband.
2. If the headband has openings in the plastic (as some of ours did), apply gauze to the exposed adhesive on the fasteners (see above on the left). This prevents the adhesive backing from sticking to the subject’s hair during use.
3. The headband is worn as it normally would, positioning the tracker on the top of the head with the plastic extending behind the ears. The elastic band fastens underneath the chin; this provides multiple points of stability, and greatly reduces accidental movement of the subject tracker during an experimental session.
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