Construction of Local Field Potential Microelectrodes for in vivo Recordings from Multiple Brain Structures Simultaneously

Researchers often need to record local field potentials from multiple structures at the same time. Our easy microelectrode design allows us to record LFPs from several brain structures at different depths simultaneously. Commercially available microelectrodes often lack flexibility and do not allow to record from multiple brain structures.

Our microelectrode design allows to easily modify the construction to fit any desired structure. Start by taking a dianal-coated nickel chromium wire 50 micrometers in diameter. Tape one end of the wire to the back of the platform and wrap the wire three times around the nearest knob on the platform.

Stretch the wire around the farthest second knob to make two loops between the knobs. Wrap the wire three more times around the first knob to fix the wire in place and tape the end at the back of the platform. Place the tension bars under the wires with the tape wrapped around them.

Using a microscope and fine forceps, make either a three-millimeter gap between the wires to make cortical, ventral-lateral, thalamic nucleus microelectrodes or a 4.5-millimeter gap to make striatal-nidral microelectrodes. If magnification is used on the microscope, ensure to calculate and adjust for the difference in magnification and the actual distance between the wires. Cut four small pieces of 0.5-millimeter-thick plastic approximately six millimeters in width and three millimeters in height.

Apply glue on the plastic. Place the plastic pieces approximately one centimeter away from the middle of the wire, which is one centimeter away from the tension bar. Remove excess glue with a cotton swab.

After the glue dries, cut the wire using fine scissors. Cut four seven-millimeter glass tubes using a commercially available kit and insert the electrode wire into the glass tubes. Put the glue at the base of the glass tubes to connect them to the plastic.

Wait until the glue dries, then cut the glass tubes and wires using a scalpel. Use super glue to attach plastics in the desired order of target regions. Apply epoxy resin around the plastic to bind the electrodes together.

Take a thick wire and make a loop on one end, dip the loop in the epoxy solution, and place it on the plastic, ensuring the thick wire is lying flat so that this wire could be used as a handle. Cut the wire to two centimeters. Group the wires and scrape away one millimeter of the isolated ends with a scalpel.

Bend the cortical electrodes and separate the wires. Using fine forceps, make a loop at the end of each wire. Hold a 10-pin headset with a hemostat and use the wooden end of a cotton swab to apply minimal amounts of flux on the pins.

Using the wooden end of the cotton swab, apply flux to the wire loops. Solder the wire loops to the 10-pin headset. Dry the headset to prevent short circuit among the pins.

Take a thin wire of about 0.05 to 0.008 inches for reference and ground wires and strip off the plastic from one end. Make a loop on the other end of the wire. Solder the stripped side of the reference and ground wires to their respective pins.

Holding the thick wire, apply cranioplasty cement around the microelectrodes, especially where the wires connect to the pins. Avoid touching the actual electrode ends with the cement. After the cement dries, put epoxy resin at the base of the glass tubes, striatal microelectrode wires, and around the whole electrode.

Avoid touching the electrode ends with epoxy resin. Local field potential recordings were performed from the right pre-motor cortex, the left VL, striatum, and SNR. Seizure start was identified as a deflection of the voltage trace at least twice the baseline.

The power spectrum plot shows the frequency distribution for the recorded local potential recordings. Seizure onset latencies could be compared between each structure with millisecond precision. A current pulse was applied at the end of the recordings to mark and confirm the location of the electrodes tips forming the lesion.

If the microelectrodes are constructed for different brain structures, remember to modify the gaps between the wires according to the stereotactic coordinates of your desired structure. Place the deep structure electrodes into the glass tubes and adjust the lengths of the microelectrodes. Then, attach the plastics in the required order.