The Electrothalamogram. ∗

Abstract

If one picks up the electrical potentials from subcortical ganglia in the hemispheres of the mammalian brain, rhythmic discharges may be recorded, as were also observed by Gerard, Marshall and Saul. 1 Yet one must bear in mind that the so-called spontaneous activity of the cerebral cortex is also manifested by bursts of more or less rhythmical waves, and that the cortex sends many centrifugal pathways to the subcortical ganglia, particularly to the optic thalamus. Thus the question presents itself as to whether the type of discharge observed on these ganglia corresponds to their own activity, also independently of the cortical influence, or whether it is due to the action of the cortex. In the present series of experiments it was tried to approach this problem in regard to the potentials led off the optic thalamus. The records of these potentials may briefly be called the electrothalamogram.

In order to obtain records of these potentials a metal cylindrical tube was screwed into a small trephine hole (diameter of the hole 7 mm.; center of the hole 8-12 mm. behind the coronal suture, 15-18 mm. laterally to the sagittal suture on the cat's skull.) This tube contained a movable hard rubber cylinder in which the electrodes could be fastened. These were concentric needle electrodes as described by Adrian and Bronk, 2 or 2 insulated silver wires with bare tips, that were coated with AgCl. The nuclei of the optic thalamus were reached in a depth of 15-19 mm.