A Micro-drive Array Method for Electrophysiological Recording from Multiple Brain Regions

Secure the rat to a stereotaxic device, then, shave and clean the skull, and start the array implantation with a 3-centimeter incision along the midline from the point between the eyes to the neck. Using a high-speed drill, make a pair of circular craniotomies between 0.7 and 1.0 millimeters in diameter above the olfactory bulb, which is 11.0 millimeters anterior and one millimeter bilateral to bregma.

Then, implant the two BR electrodes just deep enough for the tips of the screws to make contact with the brain, which is about 2 millimeters deep. Use between six and eight full turns of the screw.

Next, make another pair of craniotomies above the frontal cortex, 2.7 millimeters anterior and 2.7 millimeters bilateral to bregma. Into these holes, secure the two ground reference electrodes so they also just contact the brain, about 1.6 millimeters deep. This takes four to five full turns of the screw.

Now, plan a large circular craniotomy with a diameter of about 2.0 millimeters above the hippocampus, 3.8 millimeters posterior, and 2.5 millimeters bilateral to bregma. Then, make six to eight 1.0-millimeter holes in the area that will surround the craniotomy.

Into each of these holes, implant the anchor screws. Then, make the planned craniotomy between the screws. Above the large hole, position the integrative microdrive array such that the cannula tip is just above the large craniotomy.

Fill the gap space between the cannula tip and the brain surface with about 100 microliters of two-part epoxy. Over the next five minutes, allow the mixture to change into a transparent gel. Next, cover the cannula, BR electrodes, ground reference electrodes, and anchor screws with dental cement.

Apply about five millimeters of cement without covering the open ends of BR or ground reference electrodes. Now, solder all the open ends of the electrodes to where they connect to the board. Then, cover the bottom part of the integrative microdrive array and all electrode wires with dental cement.

It is important to completely cover the electrode wires so that the rat cannot scratch them out after the implantation. Now allow the rat to recover. After regaining sufficient consciousness to maintain sternal recumbency, house it solo without any cage mates, and give it free access to food and water.

After the surgery, gradually advance the tetrodes by advancing the screws daily. Once the tetrodes are adjacent to the target brain areas, let them settle for several days during which signals will stabilize.