Chronic Primate Recording System (16 Channel)

Adaptive Multi-Electrode Positioning Device (AMEP)
Intra-cortical brain machine interfaces usually use implantable electrode arrays with fixed-geometry. The drawback of these devices is that electrode position cannot be adjusted for signal optimization in chronic preparations. Other implantable and adjustable electrode systems allow to only push the electrodes in one direction, or cannot dealt with multiple electrodes. Here we present an adaptive multi-electrode positioning (AMEP) system for chronic implantation and motorized bi-directional electrode adjustment.
The AMEP system consists of a stainless steel chamber insert that is introduced into the implanted chamber above the intact dura.

Fig. 1: Size comparison between an AA size battery and the 16 electrode AMEP chamber insert
The AMEP can currently hold 16 quartz-glass insulated single core microelectrodes. Each of the 16 microelectrodes can be moved independently from each other in its own guide tube with 8-10mm total electrode travel. 

Fig. 2: Tip of Thomas microelectrodes used with the AMEP system. These electrodes are quartz glass insulated platinum/tungsten microelectrodes with outstanding recording performance (1, 2).

Fig. 3: Single unit activity recorded with the AMEP system on recording channel 4 in primate motor cortex.
The rear end of the microelectrode is mechanically interfaced to the electrode hook of the computer-controlled motorized Xyz-manipulator (robot). This Xyz-manipulator allows it to actuate each of the 16 electrodes individually and to move electrodes in both directions of the z-axis. 

Fig. 4: Xyz-manipulator is mounted to the AMEP chamber insert (left picture) when it is required to initially position or to reposition the microelectrodes. The xyz-manipulator gripper hooks in an electrode (right picture) and now it is possible to move the electrode up and down in micrometer steps. After all 16 microelectrodes are in the right position for recording neural activity, the xyz.-manipulator is removed and the chamber cover is closed for continuous recording from 16 microelectrodes.

Fig. 5: This picture shows the AMEP with xyz-manipulator mounted on the implanted primate recording chamber. On the left and right side of the AMEP one can see two mini cameras capturing pictures from the electrode array in the AMEP chamber insert. The camera pictures are displayed in the AMEP graphical user interface for calibration of the electrode head position (see figure 5). The cameras usually are mounted to the head post or the stereotaxic frame by customized holders (available from Thomas RECORDING)

Fig. 6: The graphical user interface of the AMEP allows to control the x-, y- and z-position of the electrodes after calibration. Therefore the camera pictures are required. After calibrating the head position of the first electrode, the xyz-manipulator is able to grip each electrode automatically!

Fig. 7: The graphical user interface of the AMEP allows to control a programmable gain main amplifier (16 channels, optional available) and a data acquisition system (32 channels, optional available). The signal of the electrode that is currently moved by the z-axis of the xyz-manipulator will be continuously displayed on the computer screen.
The bottom of the chamber insert is sealed by a silicon sheet that prevents fluids from entering the electrode guide tubes and improves the mechanical stability of the electrode recording position. The metal-shielded chamber insert houses a 16 channel low-noise preamplifier which makes the system robust against EM-noise.
In summary, the AMEP system is designed to fulfill the following specifications:
Use of quartz glass insulated platinum/tungsten microelectrodes, which are very well suited for chronic recording applications (3).
Use of a secure electromechanical connection between electrodes and preamplifier input to guarantee a low-noise transmission
Good biomechanical compatibility of the microelectrodes, which reduces the risk of a gliosis around the electrode tip
Small electrode spacing for high spatial resolution
Electrical shield around the recording electrodes to avoid electrical noise pickup from the laboratory environment
Possibility to reposition the electrodes individually with an axial μm-resolution in both directions by using a microprocessor controlled xyz-manipulator system
The AMEP system is available in two different versions:
Stand-alone version: Complete AMEP recording system with recording chamber, chamber insert with 16 electrodes and integrated preamplifier, Xyz-manipulator with motor control unit, 16 channel programmable gain main amplifier, 16 channel data acquisition system, AMEP motor control software with amplifier control and data acquisition control
Only drive version: This version is for use with other main amplifier/data acquisition systems (e.g. Plexon, TDT, Neuralynx, etc.) and consists of AMEP recording chamber and chamber insert with 16 electrodes and integrated unity gain preamplifier, Xyz-manipulator with motor control unit and AMEP motor control software
A simplified schematic diagram of the complete AMEP stand-alone version is shown in figure 

Fig. 8: Connection diagram of the AMEP stand-alone system without video cameras. The two video cameras are connected to personal computer USB ports. (click on image to enlarge）