What Is Electrocorticography?
Intracranial EEG scan. The electrodes are placed directly on the exposed surface of the brain to record electrical signals in the cerebral cortex. Can be used during surgery or in an extraoperative environment. But because the electrodes need to be implanted, it is an invasive process.
- Chinese name
- Cerebral cortex
- Foreign name
- EcoG
- Intracranial EEG scan. The electrodes are placed directly on the exposed surface of the brain to record electrical signals in the cerebral cortex. Can be used during surgery or in an extraoperative environment. But because the electrodes need to be implanted, it is an invasive process.
- history
- The EEG at the Montreal Neurological Institute was pioneered by Wilder Penfield and Herbert Jasper, neurosurgeons in the early 1950s. These two cortical electrograms were developed as part of their pioneering Montreal course of treatment for epilepsy in critically ill patients. Recording EEG cortical potentials is used to identify epileptic areas-areas of the cortex that produce seizures. These areas will be surgically removed from the cortex to remove the source of the seizures. Wilder and Jasper also used electrical stimulation during EEG recordings in patients with epilepsy undergoing surgery under local anesthesia. This step is used to explore the brain, map the area of speech, and determine that functional anatomy of the somatosensory and somatic motor cortical areas are excluded from surgical resection. Principle EEG signals consist of synchronized post-synaptic potentials (local field potentials), which directly record signals from exposed surfaces of the cortex. The potential occurs mainly in the pyramidal cells of the cortex, so it must pass through the cerebral cortex, cerebrospinal fluid (CSF), pia mater and arachnoid membrane before reaching the subdural recording electrode (outer cranial membrane). However, in order to reach an electroencephalogram (EEG) scalp electrode, the skull must also be passed. Due to the low electrical conductivity of the bone, the potential rapidly decays during this process. It is for this reason that the spatial resolution of EEG is better than that of EEG. EEG provides a temporal resolution of about 5ms and a spatial resolution of 1cm, which is very helpful for preoperative decision making. Using a depth electrode, the local field potential gives a measure of the neuron population on a spherical surface with a radius of 0.5-3 mm around the front end of the electrode. With a sufficiently high sampling rate (greater than about 10 kHz), deep electrodes can also measure action potentials. In this case, the spatial resolution is reduced to a single neuron, and the field of view of the individual electrodes is about 0.05-0.35 mm. The EEG recording was performed from an exposed electrode cortex. The surgeon must first perform a craniotomy to remove a portion of the skull to expose the surface of the brain. This procedure can be performed either under general anesthesia or local anesthesia, if needed functional cortex mapping of patient interactions. Guided by preoperative EEG and magnetic resonance imaging (MRI) results, electrodes were surgically implanted on the surface of the cortex. The electrodes can be placed on the outer dura mater (epidural) or the lower dura mater (dura mater). EEG electrode arrays are usually 16 sterile disposable stainless steel, carbon tip, platinum, or gold ball electrodes, each mounted on a ball and socket joint for easy positioning. These electrodes are attached to the overlying frame in a "crown" or "halogenated" configuration. Subdural strips and gate electrodes are also widely used in various ranges, with 4 to 256 electrode contacts. The grid is transparent, flexible, and numbered on each electrode. The standard spacing between grid electrodes is 1 cm; individual electrodes are usually 5 mm in diameter. The electrodes are on the cortical surface and are designed to be flexible enough to ensure that normal brain movements do not cause injury. A major advantage of grid electrode arrays is that they can slide under the dura to areas of the cortex that are not exposed by the craniotomy. The strip electrode and the crown array can be used in any combination. Depth electrodes can also be used to record the activity of deeper structures such as the hippocampus.