An electro-encephalography system includes an internal device for implantation below a scalp and above a skull of a patient, and an external device to be worn or carried outside the patient's body. The internal device includes a first electrode for receiving neurological signals originating from the patient's brain and a second electrode for receiving artifacts originating from sources other than the patient's brain. The external device includes a processing unit for receiving data from the internal device, mitigating the effects of the artifacts, and determining a neurological state of the patient. A therapy device is included to provide a therapy to the patient based on the patient's neurological state.