The new Heptode Mini Matrix is available for research applications with rodents or non-human primates. The Microdrive allows to move up to five fibers (single electrodes, tetrodes, heptodes, optical fibers, injection cannulas, stimulation electrodes) independently from each other to different depths of the brain. The electrode travel distance is up to 24.000 µm. A 32-channel low-noise preamplifier is integrated in the microdrive chassis. As the chassis is made of anodized aluminum it is working like a Faraday cage, shielding the recording electrodes from electrical interference. The Microdrive can be easily adapted to different stereotaxic setups e.g., for rodents and non-human primates (see figure 1).

The Heptode Mini Matrix components are shown in figure 2. The Microdrive head is exchangeable to realize different electrode arrangements (e.g. linear, concentric) with different electrode spacing (e.g. 80µm, 300µm, etc.). The Microdrive is able to record from up to 32 recording channels (if 4 heptodes and 1 tetrode is loaded to the microdrive). If the tetrode is replaced

• by an injection cannula, one can inject drugs
• by an optical fiber, one can stimulate neurons by light
• by a stimulation electrode, one can electrically stimulate neurons

and record the neural response with the reaming four heptodes (28 recording channels).

The used fiber microelectrodes have outer diameters of 80-100 µm, causing only minimal tissue damage when introduced in the recording target. In histological preparation one can hardly see the electrodes trajectories!

Figure 3 shows the Heptode Mini Matrix Microdrive connected to a motor control unit. The motor control unit has up to 8 channels so that it is possible to add further motorized devices like our motorized microinjection pumps. It is possible to control the microinjection pump with the same software that controls the Heptode Mini Matrix Motors.

Functional Connectomics with the Heptode Mini Matrix

The study of the “wiring diagram of the brain” on different scales is the focus of connectomics, a subfield of neuroscience. However, to understand information processing in a connectome, it is necessary to visualize the neural network in the brain area of interest in a living organism in real time. This is not yet possible with currently available brain research methods. The Thomas Heptode Mini Matrix together with a new 3D-reconstruction software demonstrates a new technique for the 3D-reconstruction of the position of active neurons in a neural network. The technique uses extracellular recordings with our Heptode Mini Matrix loaded with our multichannel microelectrodes (e.g., tetrodes or heptodes) and postprocessing of the recorded data by a special developed software. The principle is shown in figure 5. The 3D-reconstruction software is optionally available for the Heptode Mini Matrix system.