Most traumatic brain injuries are mild, or more commonly known as a concussion.The CHI procedure models pathologists that can occur following a mild TBI in people.The CHI protocol is highly reproducible with low variability, and only requires a single closed head impact, making the model accessible to new users.In addition to understanding how the brain changes after a mild TBI, the CHI model can be used to test therapies to speed recovery.One of the challenging steps in performing the CHI surgery is securing the animal into the stereotaxic frame.In particular, the most difficult part is placing the ear bars.This can only be learned with practice.Use a designated surgical area, such as a hood or dedicated surgical room to perform surgery.Ensure that the surgical area includes a heating pad, a stereotaxic frame equipped with an electromagnetic impactor, and an anesthesia mask designed to administer isoflurane gas.For impactor setup, select the five-millimeter probe tip.Screw the probe tip to the piston at the bottom center of the actuator, and gently tighten the probe without applying excessive force.Re-tighten the tip between impacts.Next, set up the impact velocity by rotating the large knob on the left side of the control box until an impact velocity of 5.0
