The overall goal of this procedure is to reliably determine the best electrode for acute neural recording. This is accomplished by first modifying bare electrodes in this instance through deposition of organic conducting polymers. The second step is to test the in vitro properties of the coatings.
Next, the electrodes are placed into a rat animal model for acute neural recording. The final step is to retest the electrodes in vitro to determine their bio stability. Ultimately, a comparison of different electrodes by a range of analytical techniques, including electrophysiology and electrochemistry, are used to determine key chemical and physical properties of neural implants.
This method can help answer key questions in the development of new brain machine interfaces, such as which key electrode properties can improve the signal noise ratio and the inq to bio stability. Sime and Morgan will be assisting me with this procedure. Begin this procedure by anesthetizing a rat by IP injection of urethane.
Ensure the anesthesia onset by testing for a toe pinch withdrawal reflex. If anesthesia is not sufficient, supplementary doses of urethane should be administered. Next, shave the head of the rat.
Place it in the prone position on a homeo themic plate. Then insert a rectal probe to maintain the homeo themic plate at 37.5 degrees Celsius. Afterward, place one ear bar into the approximately expected final position within the stereotaxic frame and adjust the animal in order to position the ear bar in the external acoustic acoustics.
Then align the second ear bar and place into the contralateral external acoustic mitos. After that, position the animal in order to align the ear bars with the tooth holder. Open the animal's jaw with a pair of rat tooth forceps.
Hook the upper incisors over the tooth holder and clamp the nose in place. Then make an incision in the skin of the head at approximately one millimeter to the right of the midline, and from 10 millimeters rostral to 10 millimeters. Coddle of Lambda retract the skin and muscle laterally from the incision.
To expose the parietal and inter parietal bones, scrub the surface of the exposed bone with 20%hydrogen peroxide solution and a gauze pad under the microscope. Drill a hole approximately three square millimeters in the inter parietal bone as close to Lambda and the midline as possible. Flush the hole with sterile saline to remove any bone, dust, or fragments, which may damage the electrode.
After that, dissect below the scruff of the neck with the blunt, blunt scissors. In order to create a cavity, wrap a silver, silver chloride wire with cotton wool and saturate it with saline. Then insert the reference electrode into the cavity.
Subsequently, make an incision in the dura mater on the sagittal plane. Using the tip of a needle, attach the electrode array to the electrode manipulator. Then adjust its position over the opening with a 19 degree Ros coddle angle.
Manually insert the electrode approximately two millimeters into the brain towards the inferior colus. Then attach the speaker to the left hollow ear bar. Ensure the amplifier is turned on.
After that, close the door of the recording chamber. Now deliver white noise bursts. The maximum rate at which bursts should be delivered is one burst every 200 milliseconds.
At the same time, monitor the activity on each electrode using the motorized micro drive. Slowly insert the electrode array until acoustically driven activity is recorded on the three most distal electrodes on each shank. Then perform the acoustic stimulation protocol using 300 repetitions of 50 millisecond white noise bursts with a one second repetition rate at 70 decibels, and record the multi-unit activity at each electrode at a 24.4 kilohertz sampling rate.
Slowly insert the electrode array for another 200 microns into the inferior colliculus to position each electrode in roughly the same position as the more distal electrode from the initial recording position. Then repeat the acoustic stimulation and neural recording protocol. Continue to insert the electrode array into hundred micron steps and perform the acoustic stimulation and neural recording protocol until all electrodes have recorded acoustically driven activity from at least three positions.
Afterward, retract the electrode array in 200 micron steps and continue to perform the acoustic stimulation and neural recording protocol until the initial electrode array position is achieved. Then carefully retract the electrode array manually. In this procedure, gently rinse the electrode array with distilled water to remove any contamination.
Then connect the electrode array to a potential stat. Carefully place the electrode array into the testing solution and clamp into place. Next, connect the counter and reference electrodes to the potential stat using the potential stat.
Perform sequential electrochemical impedance spectroscopy, and cyclic vol telemetry on all electrodes. A quiet time of one second is used between each test. All 32 electrodes are in contact with the solution for the full testing session of one hour.
Afterward, remove the electrode array from the testing solution and gently rinse with deionized water. Place the electrode array into an enzymatic cleaning solution for 24 hours. Then repeat the procedures again before storing the probe in a dry protective container to prevent damage and degradation of the electrode surface.
This figure shows the peri stimulus time histogram measured at each electrode averaged over 300 repetitions at 70 decibels, white noise at zero microns and 800 microns insertion depths in the inferior colliculus. The coated electrodes are indicated by asterisk, and this figure shows the streaming data measured at each electrode with 70 decibel white noise bursts at zero microns and 800 microns insertion depths in the inferior colliculus. The coded electrodes are indicated by asterisk.
The signal to noise ratio during insertion and retraction of the electrode array into the inferior colliculus is shown here. 70 decibels. White noise at the representative uncoated electrode is indicated by the dashed line, and the conducting polymer coated electrode is indicated by the solid line shown here are different sound pressure levels of 40 to 70 decibels on a conducting polymer coated Following this protocol.
Other methods like x-ray photo electron spectroscopy and mass spectrometry can be applied to understand the different types of proteins that absorb onto an electrode surface and how the different materials might be affecting these.
