Non-invasive multielectrode array for high resolution sampling of scalp-recorded potential fields

A new non-invasive electrode array has been devised to record electrical signals on the scalp. The electrodes are arranged every 10 mm in a 4 x 8 grid, thus totalling 32. Electrical coupling is assured by a column of conductor gel with a diameter of 2 mm. The electrode array has been used to record multichannel scalp potentials evoked by stimulation of the median nerve at the wrist. It was positioned on the parietal region with the midline corresponding to the external acoustic meatus. The high spatial resolution of this device allows a detailed spatial sampling of the scalp potential field where the electrical activity arising from the parietal and premotor cortex is predominant. Scalp potentials with the system are compared with those with the 10/20 system. The improved spatial resolution allows more precise localization of minimum and maximum of the potential field, though the overall distortion introduced by aliasing in the 10/20 system is not striking. Instead, the amplitudes of the fields are considerably affected by insufficient spatial sampling.