This video demonstrates a procedure to construct a head stage pre amplifier system, which simultaneously records and stimulates chronically and implanted electrodes in awake behaving animals. First, a printed circuit board is designed for a head stage with a targeted number of recording and stimulating channels. Two examples of source follower circuits are shown.
The electronic components are then sold to the circuit board and the head stage and tether cable connectors are constructed to provide an interface between the head stage and the animal's implant. With no loose connections in the system, reliable local field potential recordings can be obtained from the rat hippocampus. The main advantage of this technique over existing methods like purchasing a commercially available head stage amplifier system is that this method can be thousands of dollars cheaper and easily customized for specific stimulation and Recording experiments.
Because this method allows simultaneous recording and stimulation of the behaving brain, it can help identify and control neural mechanisms of cognition. In turn, these methods may ultimately help to improve function and treat brain disorders in people. The low cost head stage pre amplifier system featured in this video allows simultaneous neural recording and stimulation and can be made waterproof for use with swimming animals.
A completed system consists of the following components, a computer designed integrated circuit board with four recording channels and two stimulation channels. Gold pins relay brain signals to the head stage and stimulation signals to the brain by a separate connectors on the animal's head stage. A tether cable and connector relays the recording and stimulation channels through a slip ring commutator to a computerized physiology workstation.
There are two forms of waterproofing on the head stage and on the integrated circuit. Now let's take a look at the design and layout of the head stage using a commercially available software CAD package. A printed integrated circuit board with four unity gain source followers and two pass through stimulation channels is designed First, create connector pads on both sides for the pin connectors on the tether and animal connection.
A quad FET operational amplifier can accept up to four channels of plus minus input. Two power lines are needed, each of which can be connected to ground fire. 0.1 micro ferre capacitors to prevent possible induced oscillations in the operational amplifiers.
To make a unity gain amplifier circuit, route the signal into the positive input of the operational amplifier and then connect the output back to the inverting input. Then add 10 mega ohm resistors in series with the positive input to ground for the stimulation channels. Lay pass through traces connecting the outputs to inputs using VS.To guide the traces to the other layer of the bored andm back.
Finally, create a large ground plate on the backside layer to connect all vias that are meant the ground. The ground plate then should be connected to the ground pin, out to the tether and animal side. A single head stage is designed and the design pattern is tiled across a larger sheet of circuit board to provide many head stages at a lower cost.
The CAD file is transmitted to the printed circuit board manufacturing service where double-sided two layer boards are printed using top and bottom copper layers with all holes plated through the boards. Use tin lead, solar plated traces and pads that correspond to industry standard FR four laminates. Individual head stages are cut from the large tiled PCB sheet and electronic components are connected with solar.
Now let's see how to connect the electronic components. Begin preparations for soldiering of electronic components by organizing the components on the circuit board to prepare them for soldiering. Place a small amount of sold on the tin lead pad to be soldered and bring the tip of the soldiering iron close to melt in a deer.
The soldier to the pad soldier the capacitors first resistors next, and then the operational amplifiers. Because the op amps can be destroyed by overheating is a variable heat soldiering gun, and the lowest heat necessary to melt the soldier. It is best to minimize the heating time used to make a good soldier joint.
We find it convenient to create a small reservoir or soldier that flows into the footprint pad by applying soldier along the communication or power traces. Now use an O meter to test that the resistance across the resistors meets the expected value. Inspect each pad closely to ensure that no soldier is connecting or bridging adjacent pads.
If there is a soldier bridge here to melt the soldier and use tweezers to break the bridge. Now let's see how to assemble and fabricate tether interfaces. First, insert a piece of 19 gauge hypodermic tubing into one of the unused ports of the nine pin A BS socket for mechanical support.
Cut six two centimeter length pieces of insulated magnetic wire for connecting the female and phenol pins to the A BS socket. Now using a small amount of shoulder in each pin, heat the pin from the tip to shoulder the female pins to the magnetic wire. Position the male female milax pins over the pads on the tether side of the head stage and squeeze the pins over the PCB to ensure a pressure fit.
Then sold each pin to each pad in order. Next, position the ring nut over the neural implant connector and push all the female pins into the desired slots on the plastic base. Apply acrylic glue to the top of the A BS socket connector and secure it to the base of the head stage.
Finally, glue the 19 gauge tube to the tether side of the head stage for support. Now let's see how to waterproof the head stage to waterproof the head stage in case the entire integrated circuit and any exposed metal surfaces with five minutes epoxy. Allow five to 10 minutes for initial curing and 60 minutes for permanent curing.
Apply post attack putty to the surface of the nine pin a BS socket around the female pins protruding from the animal end. For maximal waterproofing, the A BS socket and a BS plug should be mated and the ring nut should be tightened. Wrap a small strip of para film around the interface to prevent water from contacting the pin connectors.
Now we'll show some representative results shown here. As an example of a successful recording. A good recording will follow an input source signal without cutting in and out during movement.
For a good reference on electrophysiology or LFPS refer to citation two. When passing a current through a particular input channel, the user should ensure that there is no crosstalk of the signal into adjacent channels. This can be done by passing the signal through each channel and testing the output of all other channels.
If there is crosstalk between channels, please refer to reference article three for useful suggestions. The user may desire the head stage to be positioned flat on the animal's head or with additional channels. We have successfully manufactured such head stages with additional channels and configurations Once mastered.
This technique can be done in an assembly line fashion to build multiple head stages at the same time so we can establish replicability and provide a quick backup for Damaged head stages. This procedure can be used in combination with other methods such as targeted drug infusion or optogenetic stimulation to investigate how different neurotransmitters and neuromodulators contribute to brain mechanisms of memory. And we used this combination of techniques to record and modify brain rhythms in the rat hippocampus, which predicted memory performance.
