Year: 2006
Type: dissertation
Abstract: The aim of this work was to map the requirements of extending the EEG recording bandwidth down to direct current (DC). Standard methods of clinical electroencephalography (EEG) are based on AC-coupled recording devices with a typical high-pass cut-off frequency at 0.5 Hz. Amplifier and electrode technology together with millivolt scale skin originated signals, have all rejected the recording of EEG signals down to DC. In the early days of EEG, high-pass filtering was introduced to prevent saturation of the amplifier, thereby making DC-stability an irrelevant topic in electrode and amplifier development. Occasionally, researchers have recorded EEG down to DC, but the needed technology and method(s) have never been widely known. This thesis presents solutions to overcome the above mentioned problems.\n\nEarly invasive experiments have shown that a significant potential difference prevails between the brain and other body tissues. However, the clinical significance and the potential diagnostic applications of infra-slow EEG signals have been a subject of little interest. This study was carried out in order to develop a method that would, for the first time, make routine bedside recording of DC-EEG possible, and to apply it in the clinic. The work included construction of a multi-channel DC-EEG amplifier that meets medical safety specifications as well as the data acquisition and analysis software. Different types of commercially available EEG electrodes and gels were investigated. The obtained results clearly point to the combination of a chloride-containing gel and silver|silverchloride (Ag|AgCl) electrodes as a prerequisite of adequate DC-EEG recording. Due to the fact that significant infra-slow skin-borne signals could contaminate DC-EEG, the means of short-circuiting the signal source in skin were studied to find one that is practical in clinical applications. Two studies were carried out to shed light on the role of the blood-brain barrier and brain haemodynamics in mechanisms underlying DC-shifts.\n\nFinally, the developed methods were applied on preterm infants and on patients with temporal lobe epilepsy. Very slow activity patterns of potential diagnostic value were observed in preterm EEG, and DC-shifts were found useful in lateralization of the origin of temporal lobe seizures. Taken together, the results indicate that DC-EEG can now for the first time be applied as a routine bedside method, and that infra-low frequency EEG data have a promising diagnostic value.
Source: Aaltodoc (Aalto University)
Author: P Tallgren
Language: English
Subfield: Cognitive Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W74684330