ECoG

Electrophysiology · reads

Electrocorticography (ECoG) is an invasive method in which electrode arrays are placed on the brain's surface, typically through surgery that opens the skull without crossing the brain's thin innermost covering. It records the pooled electrical activity of large groups of neurons, an estimated 100,000 at a time, known as local field potentials. Brain mapping and brain-computer interfaces mainly analyze the high-frequency "high-gamma" power of these signals. Standard arrays do not pick up individual neuron spikes, though specialized, very finely spaced arrays can.

Spatial resolution

1 mm

Temporal resolution

2–4 ms (recoverable timing)

Field of view

1.86–4.6 cm³ (sensing envelope)

Reads

cortical local field potential; high-gamma band power; action potentials (specialized micro-ECoG only)

Destructive?

minimally destructive

Prerequisites

surgery: Craniotomy (or burr holes for chronic strips) to place subdural grid/strip electrodes on the cortical surface, with tunneled leads to a skull-fixed connector or subcutaneous transmitter; typically followed by 7-10 days of inpatient monitoring before surgical removal in clinical epilepsy workups.

Theoretical spatial resolution

1 mm (two-source)

Theoretical field of view

213 cm³ (reachable envelope)

Description

Electrocorticography (ECoG), or subdural recording, is the recording of neural activity with electrode arrays placed directly on the surface of the cerebral cortex, typically through a craniotomy and without crossing the pia. It is invasive. It measures cortical local field potentials, the averaged activity of many neurons, rather than unit spikes; action potentials have, however, been reported from the cortical surface with electrodes at 30-micron spacing in rodents and humans. Mapping and brain-computer interfaces chiefly use the amplitude or power of the high-gamma band, about 70 to 175 Hz, sometimes together with low-frequency signals. Clinical high-density subdural recording is performed during the invasive work-up for epilepsy surgery, which requires informed consent and subdural access, typically through a large craniotomy. Fully implantable neuromodulatory systems have typically relied on ECoG because its signals have lower data-transmission demands. ECoG recordings are stable over the long term, with little need for recalibration.

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