The early DBS electrodes were quite different from the present DBS electrodes. There were four stimulation points as with recent electrodes, but the most distal stimulation point was ring shaped and the body of electrode was twisted as shown in Fig. 5.3. For the implantation of this electrode, the most distal ring-shaped part was hooked by a pointed guide needle and advanced toward the target. After that procedure, the guide needle was pulled out slowly so as not to move the tip of the implanted electrode.

The present DBS electrode is also quadripolar, but the surface of the electrode is smooth and the tip of electrode is domelike in shape. This coaxial electrode has a central stylet, and the central stylet is pulled out after the electrode is advanced toward the target. Two types of DBS electrode (models 3387 and 3389, Medtronic Co, Minneapolis, USA) are commonly used, and both have a 1.27-mm diameter. Each individual contact is 1.5-mm high, and the difference between the two models is the spacing between the contacts. The contact edge-to-edge space is 1.5 mm in the model 3387 and 0.5 mm in model 3389. Therefore, the distances from the tip of the most distal contact point to the top of the most proximal contact point for these two electrode models are 10.5 and 7.5 mm, respectively (Fig. 5.4). The design of these DBS electrodes is shown in Fig. 5.5, and the device specifications for the leads are presented in Table 5.1. In addition, other DBS electrodes such as the Medtronic model 3387 IES (diameter, 1.27 mm; contact length, 3 mm; inter-electrode spacing, 4 mm) and model 3887 (diameter, 1.3 mm; contact length, 3 mm; inter-electrode spacing, 4 mm) have been developed to cover relatively wider target areas such as the anterior limb of the internal capsule for the treatment of obsessive compulsive disorder.

The DBS electrodes are fixed into place with a combination of a plastic burr-hole ring and burr-hole cap contained in the DBS electrode package made by Medtronic Co. The burr-hole ring has a slit with a width of several mm, and small ring holes are located bilaterally beside the slit. It is possible to make the slit smaller by closing the bilateral small ring holes using pointed forceps, temporarily decreasing the diameter for placement into the perforated burr hole; once in place, the ring is released and expands in diameter to fix tightly to the burr-hole edge in the skull bone. The burr-hole ring also contains two grooves, which serve to fix the DBS electrodes. After that, the burr-hole cap is fixed to the burr-hole ring. The DBS electrodes are fixed in the groove of burr-hole ring and covered by the burr-hole cap (Yamamoto et al. 2003) (Fig. 5.6).

Tsubokawa et al. (1991) first applied MCS for poststroke pain and used the RESUME II electrode (Medtronic Co, Minneapolis, USA). The RESUME II electrode is a paddle type, single quadripolar column (1 × 4) electrode (Fig. 5.7). Recently, many more kinds of paddle-type electrodes have been developed, with different numbers of contact points (4–20 points) and columns (1–5), and different length and width paddles (Fig. 5.7).

In recent years, the Extrel type stimulation system, consisting of an external pulse generator, an antenna, and a receiver which contains the transmitter has become clinically obsolete. The Itrel type pulse generator, which is totally implanted and powered by an internal battery, is now the clinical standard. In an Itrel type pulse generator, both nonrechargeable and rechargeable pulse generators are available for clinical use. The rechargeable pulse generator must be periodically recharged with an external radiofrequency antenna, and the advantage of this system is longer duration of the batteries (up to 9 years) without need for replacement. At present, Medtronic Co. has released four types of IPGs for clinical use, namely, the Activa-PC-3761, Activa-RC-37612, Activa-SC-37602, and Activa-SC-37603. The Activa-PC-3761 and Activa-RC-37612 are multiprogrammable devices that deliver stimulation through one or two leads while Activa-SC-37602 and Activa-SC-37603 are multiprogram devices that deliver stimulation through only one lead. Only Activa-RC-37612 is a rechargeable type IPG, and the other three types are nonrechargeable type IPGs.