What is Subdural Grid?

A sheet of electrodes placed beneath the dura mater directly on the cortical surface, used clinically for epilepsy monitoring and experimentally for ECoG-based BCI research.

What category does Subdural Grid belong to in BCI?

Subdural Grid is a Devices concept in brain-computer interface science.

Subdural Grid — BCI Glossary

A subdural grid is a planar array of disc electrodes embedded in a flexible silicone sheet, surgically placed on the surface of the brain beneath the dura mater. Subdural grids are the standard clinical tool for invasive epilepsy monitoring (identifying seizure onset zones for surgical planning) and have served as the recording platform for many seminal ECoG-based BCI studies.

Clinical Use

In presurgical epilepsy evaluation, subdural grids are implanted via craniotomy and left in place for 1-2 weeks while the patient is monitored in an epilepsy monitoring unit. The grid records electrocorticographic (ECoG) signals that localize seizure onset zones with much higher spatial resolution than scalp EEG. Simultaneously, direct cortical stimulation through the grid electrodes maps eloquent cortex (language, motor areas) that must be preserved during subsequent resection surgery.

Design

Standard clinical subdural grids have 16-64 platinum or stainless steel disc electrodes (4 mm diameter, 10 mm spacing) embedded in a silicone elastomer sheet. High-density research grids reduce electrode spacing to 1-4 mm, increasing spatial resolution. The grid is connected to an external recording system via percutaneous cables that exit through the craniotomy site.

BCI Research

Subdural grids have been the recording platform for landmark ECoG-BCI studies, including the Chang lab's speech neuroprosthesis work at UCSF. The ability to record high-gamma activity (70-150 Hz) from large cortical areas makes subdural grids well-suited for decoding complex behaviors like speech articulation, hand movements, and sensory responses.

Limitations and Evolution

Standard subdural grids are temporary (removed after 1-2 weeks) and require a large craniotomy for placement. Their electrode density is limited by the disc-and-wire manufacturing approach. Next-generation devices like Precision Neuroscience's Layer 7 use thin-film fabrication to achieve 1,024 channels in a flexible array that can be inserted through a minimal craniotomy, representing the evolution of the subdural grid concept toward chronic, high-density BCI use.