A device is described, which is fully implantable and records the EEG of a person, where the device comprises a subcranial probe containing one or more electrodes, and an extracranial portion, which includes at least one electrode. The subcranial probe proceeds through an opening in the skull. The intracranial portion comprises a seal, which prevents fluid ingress or egress between the subcranial portion and the extracranial portion. Due to the high electrical resistance of the skull, the seal effectively isolates the extracranial electrode from the intracranial electrodes, making the extracranial electrode an effective ground reference for EEG recording.
