Event-Related Slow Potentials Recorded from Cortex and Depth of the Human Brain

Abstract

The discovery of the contingent negative variation (CNV) in 1963 by Walter et al. (1964) and of the Bereitschaftspotential (BP) in 1964 by Kornhuber and Deecke (1964, 1965) led to vast progress in EEG research, increasing the interest in neuropsychological research. During stereotactic interventions under local anaesthesia it was possible to record slow potential changes from cortex and various deep structures. The on-line recording of BPs was done by instantaneous opisthochronic analysis (Walter 1967). For cortical recording the method of Housepian and Pool (1962) was adopted. The flexible Teflon-isolated Ag/AgC1 electrodes were produced and chlorided by myself. They were flexible enough to be introduced through the small high-frontal stereotactic burr hole, extreme care being taken to avoid damage to small subdural vessels. Usually four subdural electrodes were introduced, two in an anterior and two in a posterior direction, the exact location always being more or less a function of chance, since the slightest resistance was an absolute indication to stop, which could sometimes be overcome by retracting the electrode and giving it another direction for advancement. The depth electrode (a coaxial probe with a pole distance of 5 mm), using the Freiburg stereotactic equipment, reaches the calculated target within a maximal error of ±0.5 mm. The recording electrodes were initially referred to the stereotactic frame (being fixed to the skull on at least four points), and later to linked mastoids. In addition to the subdural electrodes, subgaleal needle electrodes were used on the vertex and over both hemispheres.