ECoGGrids

ECoG grids, or electrocorticography grids, are arrays of electrode contacts placed directly on the surface of the cerebral cortex to record electrical activity. They are a form of invasive neural interface used primarily in clinical and research settings to monitor brain function and to localize epileptogenic tissue, as well as to study cortical processing and develop brain-computer interfaces.

Construction and configuration: ECoG grids are typically constructed on a flexible, biocompatible substrate such as silicone or polyimide and are made with electrode contacts of platinum-iridium or similar biocompatible metals. Contact diameters often range from about 1.5 to 3 mm, with interelectrode spacing commonly between 4 and 10 mm, though higher-density grids with smaller spacing (around 1–2 mm) exist for research purposes. Grids are available in two-dimensional arrays (for broad cortical coverage) and can also be configured as linear strips. Common clinical grid sizes include 8x8 (64 channels) and other multirow formats, with smaller 4x4 or 4x8 configurations also used.

Applications: Clinically, ECoG grids are employed during pre-surgical monitoring for epilepsy to localize seizure foci and to map essential language and motor areas to guide surgery and maximize functional preservation. They are also used in functional neuroscience research to study cortical dynamics and in exploratory brain-computer interface applications that translate neural signals into control commands.

Procedure and limitations: Placement requires a craniotomy and placement on the exposed cortex, usually for short-term monitoring or extended observation. While ECoG provides higher spatial resolution and better signal quality than noninvasive EEG, it records from the cortical surface and may not capture activity from deep structures. Risks include infection, hemorrhage, and inflammation, and long-term implants are limited by tissue reactions.

Signal characteristics: Recorded activity comprises local field potentials with sensitivity to clinically relevant bands, including high gamma, which often correlates with cortical activation during tasks.