1-Channel System / 4-Channel System

The Thomas Tetrode Screw Drive (TSD-02) was developed for awake behaving small animals experiments (e.g. rats). One of the biggest obstacles to chronic single unit recording is how to move microelectrodes or tetrodes into or through the desired brain area while maintaining sufficient stability to allow recording of the same cell over hours or days. Our microdrives are based around a precision screw machined to a pitch of 400μm which advances the microelectrode or tetrode in 50μm steps (1/8th turn). A spring tensions the screw and prevents it from moving spontaneously. The screw drive carries one quartz glass insulated platinum/tungsten Thomas single electrode or a Thomas tetrode.  

Fig. 1: Tetrode Screw drive (TSD-02) mounted on an implantable titanium base plate
The reusable tetrode screw drive (1) in figure 1 is mounted on an implantable titanium base plate (2). The Tetrode Screw Drive is equipped with an integrated 4 channel preamplifier. 

Fig. 2: Tetrode screw drive (TSD-2) with integrated 4 channel preamplifier mounted on a rat.
This device is intended to be used in chronic long term recording applications with freely moving rats (see figure 2). A screw driver is used to move the tetrode or single electrode up and down. The preamplifier output cable is connected to a battery power supply and a main amplifier with a thin connection cable via slip ring commutator (see figure 3) which is optional available from Thomas RECORDING.

Fig. 3: Tetrode screw drive on a freely moving rat
The tetrode screw device (TSD-2) consists of the following components (see figure 4): 

Figure 4: Tetrode Screw Drive components (1) depth control for electrode with millimeter scale, (2) implantable titanium base plate, (3) tetrode screw drive guide tube, (4) metal housing for screw drive and integrated 4 channel preamplifier, (5) screw
The Thomas tetrode screw drive moves a quartz glass insulated platinum-tungsten electrode which is shown in figure 5. The tetrode has 4 independent metal cores and an outer diameter of 100μm. Tetrodes have some advantages in comparison to single electrodes. Hargreaves et al. have tested Thomas tetrodes in comparison to FHC single electrodes and reported the results The authors did evaluate the advantages of tetrode recordings, and examined if there were any differences in terms of yield, time, and the neuronal types that could be acquired. 
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Figure 5: (A) Tetrode tip, (B) Tetrode cross section, (C) Tetrode signals
If the screw drive is mounted to the animal′s skull the tetrode can be moved up and down by turning the screw with a screw driver. Currently we plan to offer a motor unit that one can mount on the screw drive to drive the tetrode software controlled.

Figure 6: The tetrode can be moved up and down by turning the screw with a screw driver clockwise or counter clockwise.