The scientific objective is to record neural activity in healthy human subjects or neurological patients non-invasively using high-density electroencephalography (EEG). The typical recording in the laboratory is done during visual stimulation at a relatively high frequency, for example visual scene images alternating at a rate of 6 times/second
The brain has the property of synchronizing exactly at this frequency, specifically (e.g. visual regions for visual stimulation, auditory regions for auditory stimulation, etc.) which allows to objectively identify, in a frequency spectrum, the brain response related to the type of stimulation. This response can be quantified, and provide information on the integrity of information processing processes (visual recognition for our objective), their development, their location on the scalp (e.g. right posterior hemisphere, on temporal regions) as well as their temporal dimension (i.e., if familiar faces are distinguished from unknown faces, at what speed are they recognized by the brain for example, from what image quality, etc.).
The EEG system is produced by the manufacturer BIOSEMI. It allows the recording of electrical activity on the person’s scalp with a large number of channels, 128. It is scalable (a base can be accompanied by several amplification modules which allow to vary the number of recorded channels (from 8 to 256) and it includes active electrodes allowing pre-amplification of the signal at the electrode level, which reduces the noise of the measurements because the electrical impedance is as low as possible (<1 Ohm). The system records variations in electrical potential on the scalp (in microvolts), signals that are amplified, sampled (up to 2048 Hz) and filtered to be then analyzed in relation to the stimulations presented to the subject. A visual stimulator is synchronized with the EEG, as well as a response box for the participant.
