Microcontroller-based wireless recording unit for neurodynamic studies in saltwater

This paper presents the design of a biocompatible implantable neural-recording unit for Aplysia californica, which is a common sea slug. Low-voltage extracellular neural signals (< 250 ?V) are recorded using a high-performance low-power low-noise preamplifier that is packaged with programmable digital data acquisition and control, and frequency-shift keying (FSK) telemetry that provides 5-kb/s wireless neural data through 18 cm of saltwater. The telemetry utilizes an 8-cm electric-dipole antenna matched to 50 ? by exposing the ends of the antenna to the saltwater. A custom 27-MHz receiver has been developed using commercially available ICs. A clock data recovery algorithm is implemented in a microcontroller to synchronize the received data. A 3-V lithium-ion battery (160 mAh) allows 16 h of recording. Neural data obtained using extracellular nerve electrodes and a wired interface to this unit exhibit a 2.5-mV-rms noise, which is comparable to a commercial neural-recording equipment. Neural data were also collected through the wireless link, demonstrating the feasibility of low-power transmission through saltwater.