Surgical Procedure

	Anesthetize a monkey and fix the head on stereotaxic. Attach all of electrode for monitoring vital signal during surgery. Disinfect all of surgical area and cover the area with sterilized drapes.
	Incise a skin with a cautery knife. The galea aponeurotica is cut at the center and gently peeled off from skull with the knife.
	The galea aponeurotica and temporal muscle are removed from skull with scraper until all of surgical area is exposed. Tissues on skull surface have to be wiped out and all of bleeding has to be completely stopped.
	Edge of the skin and the muscles are wrapped with moistened gauze. The gauze has to be kept moistened during the surgery.Traction sutures are put at skin edge under the gauze and the suture is pulled out to ensure a sufficient working space. Drawing a planned area of craniotomy on the skull with a pencil. Circle is where burr hole will be put and lines are where craniotome will cut the skull.
	Titanium screws are implanted as an anchor for fixing a connector on the skull. This can be done after completing ECoG implantation, but it might be safer to do before craniotomy.
	Burr holes are made with a perforator. The perforator has to be placed perpendicular to the bone surface and should not stop or pull out until the drill stops. It stops automatically when it penetrates the bone. During drilling the bone, drop a saline at the hole with syringe for cooling and washing out drilled bone.
	At the bottom of burr hole, there is a very thin bone flap left. Remove the flap carefully with curette.
	Confirm no bone flap is left and dura has to be fully exposed under burr hole. Gently peel off dura from skull and make epidural space around burr hole. This has to be done in all burr hole.
	Epidural spaces between burr holes are connected. This tunnel will be a working space for Craniotome. Make sure all of epidural spaces underneath lines of bone incision are connected.
	Craniotome is cutting bone on the line. It starts from one hole to the next hole. At the hole where Craniotome is heading, suction tube is pushing dura down to make sufficient working space. Assistant is dropping saline at the cutting edge.
	Craniotome successfully cut the bone all the way around. At this point, the bone piece is still attached to dura at the center.
	Removing the bone piece. The piece has to be lifted up gently from one edge and peel off dura from the piece with spurtle. This process has to be done slowly and carefully. Otherwise, it will tear dura easily.
	Now dura is exposed. Wash the area and remove bone tips and stop bleeding if there is. Before cutting dura, put two traction sutures with 4-0 silk. The needle should not penetrate dura but scoop it at 2/3 depth of dura's thickness.
	Elevate dura with traction sutures. One suture is held by assistant and the other by surgeon. The traction sutures are used to enlarge subdural space to prevent damaging brain when opening dura. Touch dura with knife gently in between tractions and cut slowly layer by layer. Cutting doesn't have to be long. ~5mm will be fine. If you cut through dura, you will see transparent liquid (spinal fluid) comes out. But if you don't see the leakage, it is still on the way.
	Cut Bensheet in triangle shape and soak in saline. Inset the sheet into the dura hole gently. This will make safe working space for extending dura incision.
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Surgical illustrations courtesy of [Juna Kurihara]