When do epilepsy teams choose depth electrodes over a grid on the surface of the cortex? · Grey Matter

A grid needs a large opening in the skull and sees densely the surface it lies on; depth electrodes go in through small holes and sample sparse points along lines that can reach deep structures in both hemispheres.

When do epilepsy teams choose depth electrodes over a grid on the surface of the cortex?

A grid needs a large opening in the skull and sees densely the surface it lies on; depth electrodes go in through small holes and sample sparse points along lines that can reach deep structures in both hemispheres. Teams choose depth electrodes when the suspected onset is deep (the hippocampus, the insula, the bottom of a sulcus), when it could lie on either side, or when several distant regions are candidates. A grid keeps its place when the focus is near the surface and the cortex around it must be mapped finely, next to language or motor areas for example. Many centres that once relied on grids now start with depth electrodes, partly because their complication rate is lower.