1. Field of the Invention
The invention relates to an EEG monitor. The invention, more specifically, relates to a wearable EEG monitor adapted for continuously monitoring the EEG response of a user. The invention further provides a method of monitoring brain waves.
2. The Prior Art
It is generally known, particularly within medical science, to investigate brain waves by placing electrodes on the scalp of a subject, whose brain waves it is desired to measure, processing and interpreting the detected brain waves using suitable equipment. Typically, such equipment is an electroencephalograph, by means of which a so-called electroencephalogram (EEG) may be achieved. Such an EEG provides a measurement and recording of electrical activity in a subject's brain obtained by measuring the electric potential generated on the surface of the subject's scalp by currents flowing between synapses in the subject's brain. Within medical science EEG's are used for various diagnostic purposes.
A system for such a use is known from WO-A1-2006/047874, which describes measurement of brain waves by use of electrodes placed in connection with at least one of the ears of the subject, i.e. placed on an outer ear part or placed in the ear canal. The measurements are used particularly for detecting the onset of an epileptic seizure. WO-A1-2006/047874 also describes the use of electrodes in pairs, as detection and reference electrodes respectively, such a setup being well known in the field of electroencephalography.
Many known systems, like an electrode cap, use electrochemical electrodes with a conductive gel. The need for a conductive gel makes such systems rather unattractive to use in public, because the conductive gel is greasy and not confined to the area covered by the electrode. Furthermore the conductive gel is likely to short-circuit the electrodes, if they are placed in close proximity of each other. Therefore these known systems need spacing between the electrodes, leading to a large and bulky device for monitoring the EEG.
Another disadvantage of known electrochemical EEG electrode is the difficulty in creating a reliable conductive pathway from the skin of the user, to the electrode. Even when using a conductive gel, the electrical path may still be poor, due to the moist, dirt and hair at the skin of the user. This is especially a problem when the monitor is to be used for longer periods of time, where the user is active and is subjected to a non-laboratory environment, i.e. dirt, moist etc.
The known systems for measuring brain waves are generally complicated to use and require qualified personnel to operate, or require surgery to place the electrodes, and even when placed properly, there are still large variations in the recorded EEG, due to variations in the electrical coupling. Furthermore, some systems require large amounts of power to charge the input transistors of the amplifier. Despite the potential in continuous surveillance of users' EEG response in many different areas of medicine and physical science, the systems known are confined to laboratory use.