This modality is used to assess the integrity of nerves by measuring the excitability and activity of their target muscles during surgery. The resection of tumors intimately attached to nerves is facilitated by monitoring activity of muscle fibers during dissection. The surgical team is able to detect excessive electrical activity and muscle activation in circumstances when nerve fiber manipulation is nearing tolerance. Furthermore, the nerve and surrounding tumor tissue may be activated with an electrical stimulus to differentiate between the functional substance of the nervous system and non-functional tumor tissue. This technique of stimulation is commonly used as an adjunct to safety in a variety of spinal and cranial procedures.