5 min read
Updated September 9, 2025
An acute implantation places a probe for one session. The probe comes out at the end. The priorities are signal quality now, and a probe you can use again next week.
Research use only. NeuroNexus products and the procedures described here are for non-clinical research use, and must not be used in human or veterinary medical procedures.
This guide describes an approach, not a protocol. Adapt it to your species, your preparation and your institutional requirements. All procedures run under IACUC approval.
Before surgery#
Anesthesia and physiology. Follow institutional guidelines for depth and monitoring. Acute sessions run long; body temperature and hydration drift, and both show up in the data before they show up in the animal.
Instruments. Fine forceps, scissors, hemostats, scalpels and needle holders; a high-speed drill with burrs sized to the craniotomy; a micropipette or blunt needle for saline.
Sterilization. 70% ethanol and an iodine-based antiseptic. Autoclave or disinfect instruments.
Ground and reference. Stainless steel or Ag/AgCl wire, and bone screws if you are anchoring to the skull.
Rig. A stereotaxic frame with a micromanipulator, and a dissecting microscope with a cold light source. Insertion without magnification is the most common cause of a bent shank.
Check the probe first. Measure impedance before the animal is on the frame. A failed channel found at that point is an inconvenience; found mid-session it is a lost experiment.
Surgery#
Site preparation#
Secure the subject in the frame. Incise the scalp and expose the skull. Remove the periosteum with a cotton swab and rinse with saline. A clean, dry skull is what makes the craniotomy predictable.
Craniotomy#
Mark the craniotomy and the screw positions before drilling. Drill in short passes with saline cooling; heat conducted through the bone damages the cortex you are about to record from.
Size the craniotomy to the probe plus working clearance. Too small forces you to insert at an angle; too large lets the brain pulse and move.
Place bone screws for ground and reference without penetrating the dura.
Durotomy#
Some preparations need the dura removed; some do not. Where the dura is thin and the probe is sharp, leaving it intact reduces bleeding and limits brain movement. Where the shank is wide or the dura tough, remove it — a probe pushed through resistant dura will bend or break.
Insertion#
Mount the probe on the micromanipulator so the trajectory is linear and the shank is not loaded laterally.
Insert slowly. Dimpling means the tissue is being displaced rather than penetrated, and the displacement releases as the probe advances, so the final depth is not the depth you set. Slow insertion is the single highest-yield habit in acute recording.
Wet the shank with saline before it enters, and keep the craniotomy wet throughout.
Let it settle. After reaching depth, wait before recording. Tissue relaxes around the shank and units that were unstable become stable.
Reference and ground#
Wiring depends on the probe package.
16-channel probes. With a separate reference, place a reference wire in a saline-filled craniotomy, ipsilateral or contralateral. Without one, connect the probe's reference input to a bone screw near the recording site.
32-channel probes. With the internal reference, connect the designated reference wire to a bone screw. To disable it, modify the connector and reference externally.
Reference placement decides what the signal is subtracted against, and a reference in active tissue subtracts real activity. On a SmartLink headstage the referencing and grounding arrangement is set by jumpers on the headstage itself; confirm the positions with technical support before surgery, because the choice is fixed once the animal is closed.
During and after the session#
Verify before recording. Check impedance on the acquisition system and confirm activity looks like the structure you targeted.
Withdraw slowly. Fast retraction tears tissue onto the shank and is a common cause of probe damage.
Clean immediately. Rinse in distilled water and soak in an enzymatic cleaner if protein has dried on. Time matters more than technique: a probe cleaned within minutes usually recovers, one cleaned the next morning often does not.
Inspect under magnification before storing, and store in the protective case.
Troubleshooting#
Poor signal quality. Check ground and reference connections first, then impedance across channels, then the shank under magnification. In that order — the cheap checks rule out most causes.
Tissue dimpling. Slow the insertion, pre-wet the probe, and confirm the craniotomy is large enough and the dura is not resisting.
Damaged sites. Handle only by the package, never the shank. Never touch sites with metal instruments or bare hands.
Support#
Technical questions: support@neuronexus.com · +1.734.913.8858 Full protocol: Acute Penetrating Arrays ↗