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Mini Matrix System

12-Channel Tetrode System

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Mini Matrix System

12-Channel Tetrode System

The multielectrode manipulator “Mini Matrix” was developed by Thomas RECORDING in 1998. This microdrive system is based on our patented rubber tube drive also used in our multielectrode manipulator “System Eckhorn”.

The small and lightweight multielectrode manipulator “Mini Matrix” was designed to be mounted directly on a monkey head but also can be used with stereotaxic instruments available from Thomas RECORDING.

The 12-Channel Tetrode System can use up to 3 tetrodes at the same time.

Key features:

  • Axial resolution better than 1μm, x-y-z-Positioning with xyz-manipulator and special holder
  • Patented rubber-tube drive, no hysteresis, slick or free motion due to patented rubber tube drive (avoids drawbacks of cable, direct or hydraulic driven systems)
  • Electrode travel range up to 24.000μm
  • Variable speed range from 0…250μm/s, higher velocity on request
  • Small and lightweight
  • No electrode connection cables free in air! Complete metal shield around all microelectrodes
  • Suitable for cortical and deep brain recordings
  • Very close electrode spacing available (down to 80μm)
  • Different electrode arrangements available (linear, concentric, etc.)
  • Stable long-term recordings with thin microelectrodes for hours
  • Integrated low noise preamplifier


With this fiber-electrode manipulator type Mini Matrix a broad range of even very thin shafted probes can be handled, including fiber and wire-electrodes with shaft diameters down to about 25 µm. The patented driving principle of the Mini Matrix  offers an outstanding electrode positioning accuracy. Compared with hydraulic, cable controlled or direct motor driven microdrives, the patented fiber electrode manipulator “System Eckhorn” does not cause hysteresis errors of the electrode movement. Hysteresis error is generally a result of stiction and free motion of hydraulic, cable controlled or direct motor driven microdrives offered by our competitors. Our system has a higher degree of positioning accuracy due to its patented rubber tube driving mechanism being almost absolutely free of stiction and free motion.

Using Thomas Mini Matrix systems with patented rubber tube drive allows to record neural activity while the electrode is moving in the brain. So it is very easy to search active neurons in the brain.

Figure 1: System components of a 5 Electrode Mini Matrix for primate recording applications. The 5 electrode Mini Matrix is equipped with a xyz-manipulator which has a primate recording chamber clamp. We can adapt the chamber clamp to the outer diameter of the recording chamber.

The Thomas Mini Matrix systems have some advantages in comparison to other multielectrode microdrive systems for neurophysiological research presently available on the market: 

  • Vibration-free positioning of up to 5 quartz-platinum/tungsten microelectrodes in 1µm steps
  • Patented rubber tube driving principle
  • High positioning accuracy, due to lack of stiction and free motion
  • Easy exchange and calibration of microelectrodes within minutes
  • Advances up to 5 microelectrodes/tetrodes independently in 1µm steps up to 24.000µm (other electrode travel distances on request!)
  • Xyz-manipulator travel-distance: z=0-30mm, x= ±10mm, y=±10mm
  • Continuous low noise recording while the electrode scans the tissue at low velocity
  • No noise introduction in the recordings so that you can search active neurons in the brain
  • No electrode connection cables free in air, no electrical noise pickup from environment (e.g. motors, radio stations)! Competitor drives pickup electrical interference from the environment so that you for example can hear radio station music or electrical artifacts from lab devices from the audio monitor loudspeaker instead of neural spikes!
  • Electrode moving velocity adjustable (1-250µm/s), moving direction selectable
  • Microdrive with xyz-manipulator is small and lightweight
  • Low noise 5 channel preamplifier is integrated into the microdrive chassis, system is completely shielded to avoid electrical noise pickup from the environment, three preamplifier operation modes: record, electrode impedance test, electrical stimulation/lesioning
  • System is completely delivered with motor control device, integrated preamplifier, software, xyz-manipulator, chamber holder, exchangeable head, handheld remote control, etc.
  • Exchangeable manipulator head allows manifold electrode configurations and interelectrode spacings
  • Electrode spacings from 80µm up to some millimeters possible due to exchangeable Mini Matrix heads
  • The system is modular and adaptable to the end user´s requirements.
  • The Mini Matrix is usable for cortical as well as deep brain recordings in all kinds of research applications
  • User friendly computer controlled system with LAN (local area network) communication via TCP/IP protocol between motor control unit and personal computer. Software package is part of the system.
  • Using very thin shaft Thomas microelectrodes (outer diameter 80µm) causes minimal tissue damage.
  • Different neurophysiological methods are available for the Mini Matrix systems (e.g. optogenetics, microinjection)

The Mini Matrix system is available for small animal stereotaxic instruments (see figure 3 and 4) as well as for primate experiments (see figure 2).

Figure 2: 5 channel electrode Mini Matrix mounted on a primate recording chamber.

Figure 3: Mini Matrix mounted to a Thomas small animal stereotaxic instrument (SASI). By using customized adapters the Mini Matrix can be mounted on all other stereotaxic instruments presently available on the market. Please feel free to ask you your special adaptation.

Exchangeable Heads

Each Mini Matrix microdrive is equipped with an exchangeable Microdrive head. Each Mini Matrix head has up to 5 electrode guide tubes. There are different possibilities to arrange these 5 guide tubes, depending on the recording area.  Basically we have exchangeable heads for cortical, deep brain or spinal cord recordings. 

Figure 5: 5 channel Mini Matrix head with linear electrode configuration and 305µm electrode spacing.

It is very easy to exchange a Mini Matrix head by another one with other electrode guide tube arrangement or electrode guide tube spacing. The following picture demonstrates the exchange procedure.

Figure 6: Exchange of Mini Matrix head

Heads for cortical recordings

There are four  parameters of an exchangeable Mini Matrix head that can be customized:

  • protrusion of the electrode guide tubes
  • arrangement of the guide tube (e.g. linear, concentric, etc.)
  • guide tube spacing (e.g. 305µm, 500µm. etc.)
  • Sharpened of non-sharpened (standard)  guide tubes for dura penetration

The standard guide tube protrusion for an exchangeable head for cortical recordings is x=8mm, which is optimal for most recording applications (e.g. rats, mice, rodents, etc.). If you are using deep primate recording chambers we can adapt the guide tube protrusion to the depth of the primate recording chamber.

Figure 7: Mini Matrix head with linear guide tube arrangement and electrode spacing of 305µm (other guide tube arrangements e.g. concentric and other spacing e.g. 500µm)

Heads for deep brain recordings

For deep brain recording applications in small animals the normal electrode travel distance of a Mini Matrix system of 22-24 mm is enough to reach the deep brain target in rats, without introducing a cannula in the brain. For larger animals such as primates the use of a common guiding cannula with minimized outer diameter is required to bring up to 5 microelectrodes down to the recording target. Therefore we offer a special cannula technique for our Mini Matrix, invented by Dr. David Leopold (NIMH, USA). We call this technique the “Leopold Funnel Adapter”.

Figure 8: Mini Matrix head (5 channels) without (left side) and with (right side) Leopold funnel cannula. The funnel cannula guides all 5 microelectrodes together in one cannula. The electrode spacing is 80µm for single core electrodes and 100µm for tetrodes.

Figure 9: The funnel cannula is introduced in the brain down to app. 5mm before recording target under stereotaxic control. Then one drives the microelectrodes out of the cannula into the target.

Please feel free to ask for your customized deep brain recording solution! 

Heads for spinal cord recordings

Microdrive heads for spinal cord recording have a linear guide tube arrangement and interelectrode spacings from 305µm up to 10mm, depending on the researcher´s requirements. 

Figure 10: Exchangeable Mini Matrix head for spinal cord recordings. The electrode guide tube arrangement is linear and the equidistant guide tube spacing is 5mm. Other spacing (smaller or larger) is available on request.

Electrical Stimulation and 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). 

Figure 11: Mode Selection & Impedance Device consists of a (1) control box and a (2) main device which can be mounted in a 19” rack or on a workbench.

Figure 12:MSD for 5 Tetrode Mini Matrix systems. The impedance test module with the moving coil instrument is located on the right side of the front panel.

Electrical Microstimulation

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). 

Microinjection with the Mini Matrix

For making drug injection experiments with the Thomas Mini Matrix system we offer a special designed high pressure microinjection system. One of the 5 single microelectrodes of the Mini Matrix can be replaced by a microinjection cannula. The microinjection cannula (OD=120µm) has a tapered tip and is equipped with the patented Thomas rubber tube drive so that you can position the microinjection cannula tip together with the recording microelectrodes with high positioning accuracy (better than 1µm). The microinjection system consists of a special designed and computer controlled syringe pump that is connected to the microinjection cannula via a special thick wall tubing. 

The precision micromotor of the microinjection pump is controlled by the same motor control unit and graphical user interface as the Thomas Mini Matrix. This guarantees a high precision and convenient experimental control of the injection/recording experiment. 

Figure 13: Microinjection pump (A), connection of thick wall tubing to syringe cannula (B)

Optogenetic equipment for the Mini Matrix

Thomas RECORDING offers a complete range of Mini Matrix accessories for optogenetic experiments. One of the 5 single microelectrodes or tetrodes is replaced by an optical fiber (OD=120µm). The optical fiber has a tapered tip and is equipped with the patented Thomas rubber tube drive so that you can position the optical fiber tip together with the recording microelectrodes with high positioning accuracy (better than 1µm). Figure 14 shows a Mini Matrix head with concentric guide tube arrangement and a single optical fiber in the center position. The recording microelectrodes are concentrically arrange around the optical fiber in the center of this arrangement.

Figure 14: Mini Matrix concentric head with one optical fiber and 4 recording electrodes.

In figure 15 one can see a Thomas Mini Matrix equipped with a LED-light source holder. In figure 16 an optical fiber is loaded to the Mini Matrix. 

Figure 15: Thomas Mini Matrix with xyz-manipulator, LED light source and light source holder

Figure 16: Thomas Mini Matrix with LED light source and loaded optical fiber.

For further information concerning optogenetic equipment please see also our optogenetic webpage.

Selected Publications

[27] Rakesh Nanjappa, Mikayla D. Dilbeck, John R. Economides, Jonathan C. Horton, Fundus imaging of retinal ganglion cells transduced by retrograde transport of rAAV2-retro Elsevier, April 2022, DOI: 10.1016/j.exer.2022.109084

[26] Odean, N. N., Sanayei, M., Shadlen, M. N. (2022). Transient oscillations of neural firing
2 rate associated with routing of
3 evidence in a perceptual decision
, bioRxiv, February 2022, DOI: 2022.02.07.478903

[25] Khamenian MB, Kozyrev V, Treue S, Esghaei S, Dalari MR Routing information flow by separate neural synchrony frequencies allows for “functionally labeled lines” in higher primate cortex Proceedings of the National Academy of Sciences May 2019, 201819827; DOI: 10.1073/pnas.1819827116

[24] Bizley J. K., Walker K. M. M., King A. J., Schnupp J. W. H.Neural Ensemble Codes for Stimulus Periodicity in Auditory Cortex The Journal of Neuroscience, April 2010, 30(14):5078 –5091

[23] Anderson B., Harrison M., Sheinberg D. L. A multielectrode study of the inferotemporal cortex in the monkey: effects of grouping on spike rates and synchrony Neuroreport, March 2006, Vol 17 No 4

[22] Maier A., Wilke M., Aura C., Zhu C., Ye F. Q., Leopold D. A. Divergence of fMRI and neural signals in V1 during perceptual suppression in the awake monkey Nat Neurosci, October 2008, 11(10): 1193–1200

[21] Wang O., Webber R. M., Stanley G. B.Thalamic Synchrony and the Adaptive Gating of Information Flow to Cortex Nat Neurosci, December 2010 , 13(12): 1534–1541

[20] Adams D. L., Horton J. C. Monocular Cells Without Ocular Dominance Columns J Neurophysiol, 2006 , 96: 2253–2264

[19] Schoppik D., Nagel K.I., Lisberger S.G. Cortical Mechanisms of Smooth Eye Movements Revealed by Dynamic Covariations of Neural and Behavioral Responses Neuron, April 2008 , 58(2): 248–260

[18] Hohl S. S., Lisberger S.G. Representation of Perceptually Invisible Image Motion in Extrastriate Visual Area MT of Macaque Monkeys The Journal of Neuroscience, November 2011 , 31(46):16561–16569

[17] Law C., Gold J. I. Neural correlates of perceptual learning in a sensorymotor, but not a sensory, cortical area Nat Neurosci, 2008 April , 11(4): 505–513.

[16] Castellanos L. Grasping in Primates: Mechanics and Neural Basis 

[15] Lee C. W., King C. E. , Wu S. C., A. Swindlehurst L., Nenadic Z. Signal Source Localization with Tetrodes: Experimental Verification 33rd Annual International Conference of the IEEE EMBS 2011

[14] Rorie A. E., Gao J., McClelland J. L., Newsome W. T. Integration of Sensory and Reward Information during Perceptual Decision-Making in Lateral Intraparietal Cortex (LIP) of the Macaque Monkey PLoS ONE 5(2): e9308

[13] Gail A., Klaes C., Westendorff S. Implementation of Spatial Transformation Rules for Goal-Directed Reaching via Gain Modulation in Monkey Parietal and Premotor Cortex The Journal of Neuroscience, July 2009, 29(30):9490 –9499

[12] Westendorff S., Klaes C., Gail A. The Cortical Timeline for Deciding on Reach Motor Goals The Journal of Neuroscience, April 2010, 30(15):5426 –5436

[11] Gail A., Andersen R. A. Neural Dynamics in Monkey Parietal Reach Region Reflect Context-Specific Sensorimotor Transformations The Journal of Neuroscience, September 13, 2006, 26(37):9376 –9384

[10] Breveglieri R., Hadjidimitrakis K., Bosco A., Sabatini S. P., Galletti C., Fattori P. Eye Position Encoding in Three-Dimensional Space: Integration of Version and Vergence Signals in the Medial Posterior Parietal Cortex The Journal of Neuroscience, January 4, 2012 , 32(1):159 –169

[9] Gold J.I. , Law C., Connolly P., Bennur S. The Relative Influences of Priors and Sensory Evidence on an Oculomotor Decision Variable During Perceptual Learning J Neurophysiol, August 2008, 100:2653-2668

[8] Katzner S., Busse L., Treue S. Attention to the color of a moving stimulus modulates motion-signal processing in macaque area MT: evidence for a unified attentional system Frontiers in System Neurosience, October 2009, Volume 3 Article 12

[7] Bryant J. L., Roy S., Heck D. H. A technique for stereotaxic recordings of neuronal activity in awake, head restrained mice J Neurosci Methods, March 30; 178(1): 75-79

[6] Monoconduit L., Lopez-Avila A., Molat J.-L., Chalus M., Villanueva L. Corticofugal Output from the Primary Somatosensory Cortex Selectively Modulates Innocuous and Noxious Inputs in the Rat Spinothalamic System Journal of Neuroscience, Aug 2006; 26: 8441-8450

[5] Sundberg K.A., Fallah M., Reynolds J.H. A Motion-Dependent Distortion of Retinotopy in Area V4 Neuron 2006 49: 447-457

[4] Barraclough D.J., Conroy M.L. & Lee D. Prefrontal cortex and decision making in a mixed-strategy game Nature Neuroscience, Vol.7, No.4, April 2004

[3] Bruno R.M., Khatri V., Land P.W., Simons D.J. Thalamocortical Angular Tuning Domains within Individual Barrels of Rat Somatosensory Cortex Journal of Neuroscience, October 22, 2003, 23(29):9565-9574, 9565

[2] Eckhorn R., Thomas U. A new method for the insertion of multiple microprobes into neural and muscular tissue, including fiber electrdoes, fine wires, needles and microsensors Journal of Neuroscience Methods, 49 (1993) 175-179

[1] Mountcastle V.B., Reitboeck H.J., Poggio G.F., Steinmetz M.A. Adaptation of the Reitboeck method of multiple microelectrode recording to the neocortex of the waking monkey Journal of Neuroscience Methods, 36 (1991) 77-84

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