5 min read
Updated October 9, 2025
An ECoG grid is a flexible array laid on a curved, moving surface. Nothing holds it there except the fit. Placement, and the decision about where the dura goes, determine what the recording is worth.
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.
Epidural or subdural — decide first#
This is the choice that shapes the rest of the surgery, and the two approaches are not interchangeable.
Epidural. The grid sits on an intact dura. Lower risk of cortical injury, less bleeding, and a better-behaved chronic preparation. The dura attenuates and spatially blurs the signal, so high-frequency content suffers.
Subdural. The grid sits on the pia. Higher amplitude and better spatial resolution, at the cost of a dural opening, more bleeding risk, and a preparation that scars more.
Choose epidural unless the analysis needs the resolution. In chronic rodent work the epidural approach survives longer.
Before surgery#
Anesthesia and analgesia per institutional guidelines, with multi-day post-operative analgesia planned.
Aseptic technique throughout.
Instruments. Fine forceps, scissors, hemostats, scalpels, needle holders; a high-speed drill; a micropipette or blunt needle for saline. Add fine tools suited to a flexible array, and something non-abrasive to hold it with.
Materials. Dental cement or a biocompatible adhesive, bone screws, silicone elastomer for sealing, and sterile saline in quantity — the exposed surface must not dry.
Rig. Stereotaxic frame and a dissecting microscope with a cold light source.
Surgery#
Site preparation#
Secure the subject. Incise the scalp, expose the skull over the target cortex, remove the periosteum and rinse.
Craniotomy#
Size it to the grid plus working clearance. A grid fed through an undersized opening folds, and a folded array cannot be flattened once it is under bone.
Drill in short passes with saline cooling. Thin the bone before lifting the flap rather than drilling through in one pass.
Place bone screws for ground, reference and headcap anchoring, clear of the craniotomy margin.
Dural handling#
For an epidural placement, leave the dura intact and keep it wet throughout.
For a subdural placement, open the dura at the margin and reflect it. Work under magnification and control bleeding before the grid goes in. Blood between the array and the cortex is both an insulator and a source of drift.
Grid placement#
Wet the surface and the array. Place from one edge and roll into contact so fluid, not air, is displaced ahead of the array.
Air under a site is an open channel. Look for bubbles under magnification before proceeding.
Orient before you commit. Note which corner of the array corresponds to which channel and record it. A grid placed at 180 degrees produces a plausible and wrong map.
Do not press the array flat. Contact should come from the fit and from surface tension. Pressure on cortex produces a lesion and a slow drift in the signal.
Fixation and closure#
Seal the craniotomy margin with silicone elastomer, then cement over the seal and the screws. The elastomer keeps cement off cortex and stops fluid tracking into the site.
Route and strain-relieve the cable, and position the connector where it clears normal movement.
Reference and ground#
16-channel grids. With a separate reference, place a reference wire in a saline-filled craniotomy. Without one, connect the grid reference input to a bone screw near the site.
32-channel grids. With the internal reference, connect the designated wire to a bone screw. To disable it, modify the connector and reference externally.
64-channel grids. As for 32-channel, with additional reference wires; confirm the wiring for your package.
Place the reference off the recording area. A reference under the grid subtracts the activity you came to record.
Recovery and maintenance#
Analgesia and monitoring per institutional guidelines; individual housing with nesting material that cannot catch the implant.
Check impedance at implant and at each session, and inspect the perimeter for cement lifting or fluid accumulation.
Troubleshooting#
A block of channels is flat — contact, not electronics. Air, blood or a fold under that part of the array.
Amplitude falls over the first two weeks — expected in subdural preparations as the surface reaction develops; a steeper fall suggests fluid under the grid.
Slow drift within a session — temperature, or fluid accumulating under the array.
All channels are noisy — ground and reference first, then shielding, then cable routing.
Grid care#
Inspect under magnification before each use and check channel continuity. Rinse immediately after use with sterile saline. Store flat and protected; a crease in a polyimide array is permanent.
Support#
Technical questions: support@neuronexus.com · +1.734.913.8858 Full protocol: ECoG Arrays Guideline ↗