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Thomas Matrix

32-Channel Heptode Thomas Matrix System

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Thomas Matrix

32-Channel Heptode Thomas Matrix System

The multielectrode manipulator “Thomas Matrix System” is the latest development of Thomas RECORDING engineering department and a new generation of multielectrode Microdrive systems on the world market. This system uses the very precise Thomas rubber tube drive for parallel independent insertion of up to 32 fiber microelectrodes (single electrodes, tetrodes or heptodes, diameter=80-100µm) through the intact dura into the brain of chronically prepared animals.
The max. electrode travel distance of each fiber microelectrode is up to 35mm (electrode travel extensions are possible and available on request!).

A 224-channel low noise preamplifier is integrated in the microdrive metal chassis. The microelectrodes are completely shielded by the microdrive chassis (working like a Faraday cage) so that electrical interference from the laboratory environment does not cause noise problems. Due to the rubber tube driving principle of the Thomas Matrix it is possible to record neural signals while the electrodes are moving in brain tissue!

Key features:

  • Axial resolution better than 1μm, x-y-Positioning with a grid 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 35.000μm
  • Variable speed range from 0…250μm/s, higher velocity on request
  • 32-Motors and 224 recording channels
  • Drive can be used with electrodes, tetrodes, heptodes, injection cannulas, optical fibers
  • 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, 4×8, 2×16, concentric, etc.)
  • Integrated 224 channel low noise digital pre- and main amplifier with data acquisition
  • Optogenetic and microinjection extension available
  • Heptode32ThomasMatrix Image1
Technical Data
Microdrive Technical Data 
Number of motors:32
Electrode travel distance per channel:up to 35.000µm
Resolution per step:1µm
Max. electrode speed:up to 250µm/s
Electrode driving principle:patented Thomas rubber tube drive
Motor control:via included software and microprocessor motor control unit
Pre-Amplifier Technical Data 
Number of channels:224
Recording bandwidth:
Gain per channels:
Pre-Amplifier input:

Preamplifier supply voltage:

Operation modes on each channel:

Recording, Stimulation/Lesion, Impedance Test

Stimulation modes:

optical, electrical, drugs

Microdrive System

The scalable 32 Heptode Thomas Matrix System can position up to 32 Heptodes (with up to 224 recording contacts) in a small brain area (minimum 2.4×1.2mm). This system is available in a 4-, 7-, 16– and 32-heptode Version. The microdrive is equipped with the patented Thomas rubber-tube drive that avoids positioning errors well known from other microdrive systems [Eckhorn R, Thomas U (1993); A new method for the insertion of multiple microprobes into neural and muscular tissue, including fiber electrodes, fine wires, needles and microsensors. J Neurosci Methods 49:175-179.].





Figure 1: 32 Heptode Thomas Matrix drive with the following features:

(1) Stainless steel guide tubes,

(2) exchangeable microdrive head for different electrode configurations (e.g. linear, concentric, etc.),

(3) 224 channel preamplifier integrated in the Microdrive chassis,

(4) Thomas Matrix chassis with closed cover.





The 32 Heptode Thomas Matrix has an integrated 224-channel low-noise preamplifier. The microelectrodes are shielded by the microdrive chassis resulting in no electrical noise pickup from the environment.
Different electrode configurations are realized by an exchangeable microdrive head. Very close electrode spacings are possible (down to 95µm). The 32 Heptode Thomas Matrix is well suited for cortical and also for deep brain recordings. The electrode travel distance is up to 35mm, larger travel distance on request!
The 32 Heptode Thomas Matrix System is delivered completely with microprocessor motor control unit, software, multichannel preamplifier, xyz-manipulator, and a set of microelectrodes.
The heptodes consist of 7 individual platinum/tungsten cores (Fig. 2) and support spike sorting based on the stereotrode effect (Fig. 3), which allows superior single unit isolation as compared to typical spike sorting techniques (e.g. template matching) [2].




Figure 2: Heptode cross section and dimensions. This drawing shows the cross section and dimension of a 3D-heptode





Figure 3:
2D-Heptode recording channels




Integrated Software

The integration of Thomas RECORDING multichannel motor control software and the intan TECHNOLOGIES data acquisition hard– and software in one graphical user interface allows to drive each heptode, tetrode or electrode independently from each other while the signal from every recording channel is continuously displayed on the monitor screen (see figure 4 below).




Figure 4: Graphical user interface of the motor control and data acquisition software for the 32 Heptode Thomas Matrix system. This software allows simultaneous display of electrode position and signals recorded at this electrode position.



This software offers all controls and information necessary to position a recording electrode in the target, for example controls for electrode moving direction and speed, displays for penetration depth as well as relative and absolute electrode position. Signals from all channels are recorded while the electrode is moving and are displayed continuously on the monitor screen.

Moveable Electrode Arrays

In contrast to fixed electrode arrays like silicon probes or Utah arrays (see figure 5A) our 224 channel recording system offers individually moveable electrodes, tetrodes or heptodes (see figure 5B). The Thomas fiber electrodes cause only minimal tissue damage, which allows to use them many times in the same recording area.

Figure 5A: Fixed silicon probe array                         Figure 5B: Array with 32 moveable heptodes

The 32 Heptode Thomas Matrix is able to move the 32 fiber-electrodes, -tetrodes or –heptodes with an axial resolution of 1µm. The maximum electrode travel distance is 35.000µm (longer travel distances on request). The lateral spacing of the electrodes can be varied by using distinct exchangeable heads with other electrode spacings (305µm, 500µm, 750µm etc.). It is also possible to select between different electrode arrangements like linear 1×32, 2×16, 4×8, concentric, etc.

Automatic Heptode Movement

The 32 Heptode Matrix is a novel multi-electrode recording system that is able to automatically position heptodes inside the brain by isolating and analyzing single unit activity unsupervised. The automatic heptode positioning allows to improve the quality and efficiency of acute multichannel recordings.




Figure 6:
Automatic heptode positioning: The extracellular signals are recorded by the heptodes (C) and amplified and digitized by the Thomas Matrix (A). The signals are processed by a specialized computer algorithm (B). The algorithm decides automatically to move the electrode forth or back depending on the recorded extracellular signals, until the signal quality is optimal.






This feature is currently under development and will be available soon!


The 32 Heptode Thomas Matrix software platform has an interface to the neuronavigation software of our partner cortEXplore (Austria, This enables the researcher to create a precise 3D-representation of The recording subject based on multi modal medical images, such as CT, MRI and fMRI.



Figure 7:
The 32 heptode Thomas Matrix system has an interface to the cortEXplore neuronavigation software. The position of the Thomas Matrix drive and the electrodes (A) are displayed on the monitor (B) of the cortEXplore system (C).









Skin, bones, blood vessels, cortex and activated brain areas constitute the basis for planning neurophysiological experiments in depth within minutes. The software interface allows to project the anatomy on the computer screen to observe the experiment plan at real scale and in 3D.

Neural Network Reconstruction

The 3D-reconstruction of the neural network from the heptode data is a feature currently under development. Similar to microscope the system will display the neural network on a cellular level, by showing active neurons around the heptode tip in a micrometer scale.




Figure 8: 3D-reconstruction of the neural network around the heptode tip. The microdrive (A) places up to 32 heptodes in a small brain area of max. 2.4 x 1.2 x 35 mm which spans a voxel of brain tissue of about 100mm3. Each heptode (C) records the brain activity from multiple neurons in the close environment of the heptode tip (D). The Thomas heptode sorter and 3D-reconstruction algorithm calculates the position of each active neuron near the heptode and displays the result on the computer screen of the system (E). This unique feature offers new opportunities for neurophysiological research experiments like connectome research.




Around each heptode tip, neurons in an area of approximately 100µm will be reconstructed, since the signals will fade out into noise for larger distances. As the distance between two heptodes in our microelectrode manipulator can be down to 200-300µm, one can reconstruct a complete brain voxel of a few cubic millimeters, e.g. with an 8×4 array of movable heptodes. Our system will allow to graphically depict the activity of the living brain on a neuronal level and to observe changes in real time, e.g. caused by neuropharmaceuticals or microstimulation in another area.

Optogenetic, Drug Injection, Electrical Stimulation, Transmitter Measurement

The 32 heptode Thomas Matrix allows to replace single electrodes by stimulation electrodes, injection cannulas or optical fibers. This allows to stimulate the neurons with electrical current,
by drug injection or by light and to record the response of the neural network with the recording electrodes, tetrodes or heptodes.



Figure 9: The left side of the picture shows the techniques that can be combined in the Thomas Matrix drive. You can move recording electrodes (e.g. single core electrodes, tetrodes, heptodes), stimulation electrodes for electrical stimulation, injection cannulas for drug pressure injection as well as optical fibers for stimulation with light via LED or laser. Of course you can also use any combination of these techniques. For example inject drugs and record the response of the neurons with the remaining recording microelectrodes.

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Selected Publications

[2] McNaughton BL, O‘Keefe J & Barnes CA (1983), The stereotrode: A new technique for simultaneous isolation of several single units in the central nervous system from multiple unit records.J Neurosci Methods 8:391-397.

[1] Eckhorn R, Thomas U (1993), A new method for the insertion of multiple microprobes into neu-ral and muscular tissue, including fiber electrodes, fine wires, needles and microsensors.J Neurosci Methods 49:175-179.

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