Abstract :
[en] Implantable microelectrode arrays for chronic neural recordings receive an attention by a number of research groups investigating ensemble spike activity and local field potentials. Due to that interest, various types of arrays have been developed. In the present study we compared the LFP signals recorded from the ventral tegmental area (VTA) of freely moving male Wistar rats using the two types of arrays: microelectrode microwire arrays, and silicon-based planar probes. Our choice was based on the difference in the geometry of these two array types. The microwire electrodes have a three-dimensional recording surface around their tips. This allows them to receive the signal from the diverse brain regions. In contrast, the electrode contacts of the planar probe are patterned on one side of the silicon shaft (often named top-side, in contrast to the other, back-side). This configuration mainly allows registering the signal from the top-side of the shaft, while the signal from the back-side gets attenuated. Microwire arrays used in this study consisted of 8 sharpened platinum iridium wires, coated with parylene-C, except for the tip allowing the recording (Alpha Omega GmbH, Israel). Planar probes (ATLAS Neuroengineering, Belgium) had 16 iridium oxide electrode contacts implemented in the 4 silicon shafts, 4 electrode contacts per shaft. The recording was performed using a wireless system (W-Basic-System, Multi Channel Systems MCS GmbH, Germany). The probes were implanted in two orientations: top-side facing the midline, and top-side facing the lateral plane of the brain. For verification of the recording area the rats were anaesthetized and perfused with 4% paraformaldehyde containing 1 % of Gadovist. The brains were removed from the skull and placed in Fomblin for MRI scanning (9.4 Tesla MRI DirectDrive VNMRS, Agilent Technologies, Palo Alto, CA). Frequency spectra of LFP recorded by the microwire arrays, and by the planar probes oriented to the lateral plane of the brain contained a prominent peak in the theta range (6-8 Hz). In contrast, the signal registered using the planar probes oriented to the midline lacked such a peak and was more heterogeneous. We attribute the observed difference to the geometry of the recording platforms.
