neurophysiology recordings in cortical tissue of marmoset

Development of an X-Y Electrode Stage for Precise Neural Recording in Marmosets

The common marmoset (Callithrix jacchus) has quickly grown in popularity as a model to study brain function in recent years. This growing popularity is due to the accessibility of the marmoset&#39;s smooth cortex, the similarities in neural functional organization with humans and other primates, and the small size and fast breeding rate1. As this model organism has grown in popularity, there has been rapid development in the neurophysiological techniques suited for use in the marmoset brain. Electrophysiology methods are widely used in neuroscience to study the activity of single neurons in the cortex of both rodents and primates, resulting in unparalleled temporal resolution and location access. Due to the relative novelty of the marmoset monkey as a model of visual neuroscience, the optimization of awake-behaving electrophysiology techniques is still evolving. Previous studies have shown the establishment of robust protocols for electrophysiology in anesthetized preparations2, and early awake-behaving neurophysiology studies have shown the reliability of single-channel tungsten electodes3. In recent years, researchers have established the use of silicon-based microelectrode arrays for awake-behaving neurophysiology4. However, the marmoset poses unique targeting challenges due to its small brain size and lack of anatomical landmarks. This protocol outlines how to construct and use a micro-drive recording system suitable for the marmoset that allows for the recording of large populations of neurons with silicon linear arrays while producing minimal tissue damage.
Working with the marmoset poses a challenge due to the smaller scale of the retinotopic maps in the visual cortex as compared to larger primates. A slight shift of the electrodes by just 1 mm can result in significant changes in the maps. Moreover, researchers often need to alter the placement of the electrodes between the recording sessions to obtain a broader range of retinotopic positions in the visual cortex. Current semi-chronic preparations do not allow for the adjustment of the electrode positioning daily or with enough precision to target specific locations at sub-millimeter scales5. With this in mind, the proposed micro-drive system utilizes an X-Y electrode stage that mounts a lightweight micro-drive to a recording chamber and allows for the sub-millimeter targeting of cortical sites. The moveable X-Y stage components allow for vertical and horizontal movement of the linear array in order to traverse the cortical areas systematically, which is required to identify areas of interest (via retinotopy and tuning properties). Across recording sessions, researchers can also manually adjust the X-Y stage to shift the targeted sites within the area. This is a key advantage over alternative techniques using semi-chronic recording preparations, which do not have easy electrode targeting mechanisms.
The micro-drive is a versatile tool that enables the attachment of various silicon arrays to be mounted for lowering into the cortex. In this protocol, a custom probe with two 32-channel linear arrays spaced 200 &#181;m apart was used for the investigation of laminar circuits spanning the cortical depth. Most methods for probing the neural circuitry typically sample the electrical potentials or single units averaged across all the layers of the cerebral cortex. However, recent research has revealed intriguing findings about cortical laminar microcircuits6. By utilizing the micro-drive, researchers can use laminar probes and make fine adjustments to the recording depth to ensure comprehensive sampling across all the layers.
This system can be constructed with commercially available components and is easily modified for different experimental techniques or probes. The key advantages of this preparation are the ability to change the X-Y recording position with sub-millimeter precision and to control the depth of the recording within the cortex. This protocol presents step-by-step instructions for constructing the X-Y stage micro-drive and neurophysiology recording techniques.

Author Spotlight: Optimizing Micro-Drive Systems for Precise Electrode Positioning in Marmoset

Electrophysiology of Laminar Cortical Activity in the Common Marmoset

The common marmoset poses unique challenges for neurophysiology due to its small size and lack of gyre as anatomical landmarks. A slight shift of the electrode by just a millimeter can result in significant changes in the retinotopy map. The proposed micro drive system utilizes an XY electrode stage that allows for vertical and horizontal movement on a sub millimeter scale.Due to the relative novelty of the marmoset monkey as a model for visual neuron sign, awake behaving electrophysiology techniques are still evolving. Current preparations often use semi chronic probes that do not allow access for the positioning mechanisms. This protocol demonstrates a lightweight micro drive for useful linear array recordings, which allow flexible positioning across sessions to map out retinotopy within the chamber.Long-term cortical damage can be avoided in the preparation when used correctly with the secure drive, slow penetration of tissue, and avoidance of major blood vessels. Additionally, the use of silastic in the craniotomies to avoid infections has been optimized in this technique.

Neurophysiology Recordings in Cortical Tissue of Marmoset

To begin, secure the micro-drive on a head cap. Secure all three screws on the micro-drive system. Using the screw control on the micro-drive, lower the silicon probe, making one turn every 1 to 2 seconds until units are observed at the array tip.Once the neurons are observed, retract the one turn of the micro-drive to decrease the electrode's speed of entry as it moves through the Silastic and dura into the cortical tissue. Slowly continue to drive the array into the cortex, advancing 4 to 6 turns over 20 to 30 minutes until neurons are evenly distributed across the length of the probe. Then slowly retract the array by 1 to 2 turns to reduce the pressure on the tissue.After the recording is complete, slowly retract the array from the cortex at a speed similar to the initial insertion. Once no more neurons are visible on the probe, retract the array more quickly until it returns to the fully retracted starting position. After removing the probe from the recording chamber, soak it in contact lens solution for 20 minutes to clean off any tissue or blood.Place the probe in alcohol for one minute to remove the contact lens solution and allow the electrode to dry. The spike sorted array data obtained through Kilosort revealed that the principle component features of selected spikes in a cluster were distinct from background spikes, confirming the recording's stability over time. The reliability of the X-Y positioning demonstrated a 70.8%overlap in mean RF locations between two sessions a week apart.Precise retina topic space movements were observed in a series of recording sessions crossing the MT and MTC borders using minor positioning changes.

neurophysiology-recordings-in-cortical-tissue-of-marmoset

Research

JoVE Journal

Neuroscience

The marmoset monkey provides an ideal model for examining laminar cortical circuits due to its smooth cortical surface, which facilitates recordings with linear arrays. The marmoset has recently grown in popularity due to its similar neural functional organization to other primates and its technical advantages for recording and imaging. However, neurophysiology in this model poses some unique challenges due to the small size and lack of gyri as anatomical landmarks. Using custom-built micro-drives, researchers can manipulate linear array placement to sub-millimeter precision and reliably record at the same retinotopically targeted location across recording days. This protocol describes the step-by-step construction of the micro-drive positioning system and the neurophysiological recording technique with silicon linear electrode arrays. With precise control of electrode placement across recording sessions, researchers can easily traverse the cortex to identify areas of interest based on their retinotopic organization and the tuning properties of the recorded neurons. Further, using this laminar array electrode system, it is possible to apply a current source density analysis (CSD) to determine the recording depth of individual neurons. This protocol also demonstrates examples of laminar recordings, including spike waveforms isolated in Kilosort, which span multiple channels on the arrays.

Custom-built micro-drives enable the sub-millimeter targeting of cortical recording sites with linear silicon arrays.

The marmoset monkey provides an ideal model for examining laminar cortical circuits due to its smooth cortical surface, which facilitates recordings with ...

Construction of the Electrode Micro-Drive and Polytrode Plating of Electrodes for Neurophysiology Recordings

To begin, collect the parts required for the construction of electrode micro-drive. Place a nut in the slot of the base and add super glue for stability. Then insert a screw through the nut in the base.Using a rotary tool with a diamond wheel cutting attachment, cut a four by three by three millimeter section of the plastic grid with one by one millimeter hole spacing. Place the grid section onto the top of the Y stage. Apply epoxy to fix the grid section onto the top of the Y stage.Then fit the micro-drive over the grid using a screw. Add epoxy at the base of the micro-drive for stability. Attach a plastic rectangular platform to a 28 gauge steel tube using epoxy, thread a 23 gauge guide tube through the grid.Then thread the steel tube attached to the plastic platform through the 23 gauge guide tube. Place the 28 gauge steel tube into one of the micro-drive slots. Secure the steel tube to the micro-drive with epoxy.Using a hand tapping tool, tap the pre-made screw holes in the X stage and base to build the base for the drive. Then insert screws through the long slots in the X stage. Secure them in the corresponding screw holes of the base.Insert two screws through the long slot in the Y stage and secure them to the pre-made screw holes in the X stage. After ensuring the micro manipulator drive is outfitted with a plastic platform, use tape to attach the 64 pin connector to the platform. Then carefully place a dab of bacitracin onto the plastic tube and attach the electrode connected to the 64 pin connector using a flexible ribbon cable.Using the micro manipulator drive, hold the silicon electrode and its connector while threading the plastic tube through the hole in the Y stage. Detach the 64 pin connector from the micro manipulator drive and use glue gel to secure the connector to the platform on the X stage. The next day, carefully detach the electrode from the plastic tube and remove the micro manipulator drive from the assembly.Gently move the alligator clip to flip the drive over to see the unsecured electrode. Place the electrode onto the plastic holder below the Y stage and secure it with silicone elastomer. After five minutes, using the screw control on the micro-drive, retract the electrode and place the protective sleeve over the electrode.Tighten the three side located screws on the base component of the micro-drive. Connect the head stage for recordings onto the 64 pin connector. To prepare the PDOT solution, combine EDOT and PSS in distilled water a day before the use.Open the impedance tester software and in the upper dropdown menu at the top left, select the adapter. In the second dropdown menu, select the electrode. Ensure that the number of channels is correct.Using a connector, connect the probe to the impedance tester system and lower the probe into grounded saline to obtain a baseline reading. Press the test impedances button and verify the correct setting before pressing the test probe button. Record and save the baseline readings for future reference for both shanks of the electrode.Next, lower the lab jack to remove the probe from the saline. Replace the saline in the beaker with distilled water. Raise the lab jack to submerge the electrode and rinse the remaining saline solution before lowering the lab jack again.Replace the distilled water with PDOT solution and raise the lab jack until the electrode is submerged. Select the DC ELECTROPLATE button and verify the correct settings. Then press the Autoplate button and save the results.After testing, first, rinse the probe with distilled water, then fill the beaker with saline, and raise the lab jack until the electrode is submerged. Press the test impedances button and check for the correct settings. Then press the test pro button.