Implanted electrodes for stimulating or recording from deep-lying brain structures.

Abstract

Recent studies (1-5) of brain stem mechanisms and their influences upon the electrical activity of the cortex have suggested the desirability of recording cortical and diencephalic electrical activity in normal, unanesthetized cats during states of sleep and wakefulness. In order to record from or stimulate deep structures of the brain, a method of permanently implanting electrodes has been developed along the lines begun by Harris(6) and Hunter and Jasper(7). The possibility of wider application of this technic leads to detailed description here. A permanently implanted electrode system for this purpose must meet three major requirements. It must be capable of precise placement or localization in order to explore systematically the matrix of small nuclei in the subcortical regions of the brain. It must be sufficiently durable to maintain electrical insulation in the presence of tissue fluids. It should not produce undue tissue reactions and irritability. A simple extension of the principles of stereotaxy permits accuracy of placement and satisfies the first criterion. Durability and non-irritability have been achieved by the proper selection of materials. Previous methods of implanting electrodes have used the Horsley-Clarke instrument for orienting the electrodes which are fixed into position by cementing them to sockets screwed into the calvarium. In the present method a new horizontal reference plane is established by attaching a flat base plate to the cranium parallel to the original Horsley-Clarke H (horizontal) reference plane. A second plate carrying the electrodes at predetermined H and L-R (left-right) positions is brought into place with the Horsley-Clarke instrument and cemented permanently to the base plate. In this manner several electrodes may be placed accurately to varying depths over a wide area. Materials and procedures. The following sections describe in detail the construction of the various parts and sub-assemblies in this order.