Lamp-Only ISL

In our experiments with implanted ISLs, the A3030D has been plagued by lamp artifact caused by water carrying the lamp voltage out of the head fixture and into the animal body, where it corrupts the EEG signal. Ceramic dual-bore collars around the lamp leads stop the water conduction, but the seal within the collar can still fail, and when it does, the EEG signal is compromised. The A3030D-LO is designed to remove the concern of seal failure from an optogenetics experiment by removing the EEG pick-up leads alltogether. We combine the A3030D-LO with a separate subcutaneous transmitter to monitor EEG. The EEG and lamp power circuits are now separated and their battery power supplies are floating with respect to the animal body. Failure of the collar seal will introduce some artifact into the EEG signal, but two orders of magnitude less than if the EEG X− lead is connected to the lamp power 0 V at the same time the seal breaks.

We take two A3030Ds, D7.11 and D7.6, and dismantle them both. We remove their batteries, antennas, lamp leads, and sensor leads. We load new sensor leads with collars and new antennas. We do not load EEG leads. The result is the A3030D-LO, the Lamp-Only version of the ISL. The EEG amplifier is still operational. The device will transmit data and acknowledgements.


Figure: Implantable Sensor with Lamp, Lamp-Only Version (A3030D-LO).

We take care to make sure the pins are soldered in the correct direction on the leads. Looking at this picture we see that the positive (orange) lead must be in the foreground when the pins are pointing to the left. Otherwise the implanter has to rotate the pins. The length of lead from the collar to the pin is 5 mm so the implanter will not need to fold the leads within the head fixture, but instead can build the head fixture directly over the pins and collar. The devices are encapsulated in black epoxy using our rotator procedure, and then coated in SS-5001 silicone, with extra silicone applied to the sharp corners. The result is not pretty, but it is resilient and flexible.


Figure: A3030D-LO Lamp Artifact, 10 ms pulses.

The figure above shows the artifact we see on the disconnected EEG signal when we flash a white LED with a 40-mA lamp current at 100% brightness. We will ship these two devices to ION/UCL this week.