Wireless recording of neuronal activity

Introduction ------------ In brain activity recordings, conventional systems require a bunch of cables for attaching micro-electrodes being placed close to relevant neurons. Depending on the setup an extensive constraint of the head's movement is necessary. The rapid development of microelectronics especially for smartphones promotes the miniaturisation of affordable, wireless electronics for specialised use cases. Our approach was to develop a wireless recording system which can be mounted on monkey's heads. Methods ------- We developed a wireless measurement system for extracellular recordings using a cascade of low noise input amplifiers a Bluetooth module for wireless transmission and a high capacity 32-Bit microcontroller for signal processing. The electronic boards are stacked in a compact two layer array and contain a motor driver to reposition the electrode's tip during an experiment. Thus we have a bi-directional communication a readjustment of many parameters such as amplifier settings is feasible. The designs is mountable on conventional stationary cable-based system to compare to an established setup. Therefore neuronal recording was done using the proved setup and a switch over to our wireless system after a stable recording condition was adjusted. For further compensation of the electrode's position drift the motor control was handed over to the newly developed wireless system. Results ------- We successfully recorded neuronal spikes while the monkey was doing a pre-trained experiment. Using the backchannel it was possible to leave the active region and return to it, showing that a cable-free repositioning of the electrodes is possible. Due to a still too limited bandwidth of the Bluetooth module we were only able to transmit one channel at a time even though monitoring of up to four connected electrodes is possible. Regarding size and weight the energy storage is still the dispositive part in mobile metering systems. Conclusion ---------- A working wireless recording system for neuronal activity is shown, even though a higher bandwidth for multi-channel recordings is desirable