Mode Selection & Impedance Test Device (MSD)
The Mini Matrix preamplifier is integrated in the microdrive chassis and has three operation modes: Recording / Electrode Impedance Test /Stimulation or Lesioning. The standard operation mode of the preamplifier is “Recording”. To use the other two modes Thomas RECORDING offers a special designed device that is called Mode Selection & Impedance Test Device (MSD).
The MSD-3 is suited for the Thomas RECORDING Mini Matrix System with 3 single electrodes.
The MSD is available for Electrode and for Tetrode Mini Matrix systems.
Each MSD consist of a main device housed in a 19” rack mountable cabinet (2 in figure 1) and a small control box (1 in figure 1).
Electrode Impedance Test
The MSD is equipped with a special low current impedance test unit that allows measuring the electrode tissue impedance of each microelectrode while the electrode is in the brain. The constant current is so low (5nA) that it does not stimulate nerve cells in the brain. The electrode impedance value is displayed on a moving coil instrument. We have used this kind of instrument instead of digital because moving coil instruments better display fluctuations in the impedance value which is important especially when electrodes penetrate tissue borders (e.g. primate dura mater).
The preamplifiers of our Mini Matrix systems are prepared for electrical stimulation and lesioning. You can pass a stimulus or lesioning current through each of the 5 microelectrodes. A Mode Selection & Impedance Test Device (MSD, see figure 12) is required as well as a microstimulation generator. Both devices are available from TREC on request. Especially for microstimulation we offer special coated Thomas microelectrodes. The microstimulation electrode tips are coated with iridium oxide. This coating increases the charge transfer capacity of our electrodes dramatically which makes them very well suited for stimulation experiments. <
Setting lesions with Thomas microelectrodes
At the end of a recording session you might want to mark the recording position of the recording electrode. In this case you can pass a lesion current through our standard microelectrode tip. It could be shown by Robert Shapley and colleagues, that small dc currents make good lesions in primate visual cortex without any electrode tip damage (see unpublished report).