Development of an implantable sensor for recording neural activity in the auditory pathway of rats

Introduction: Ensuring the secure and efficient application of invasive microelectrode arrays (MEAs) in chronic experiments is crucial. Therefore, this study aims to develop an implantable multi-channel MEA for simultaneous neural activity recording in the auditory cortex (AuC) and medial geniculate nucleus (MGN) of rats. Methods: We utilized 32-channel tungsten tetrode arrays, comprising eight tetrodes, each constructed from four twisted microwires with a diameter of 15μm, coated with 1.5μm-thick isonel insulation. The tetrode lengths varied based on the region (5.4 or 5.8mm), maintaining a minimum spacing of 300μm. The tetrodes were threaded through an acrylic template (5 x 4mm) containing stereotaxic coordinates of target regions in the left hemisphere. Subsequently, the wires were secured with composite resin, and a printed circuit board connected to an analog headstage (Plexon) was affixed to the template. Array coordinates were organized based on a rat brain atlas, focusing on auditory regions of interest: primary AuC (Au1, tetrodes 1Au1 and 2Au1), secondary AuC dorsal (AuD) and ventral (AuV), MGN ventral (1MGV and 2MGV) and dorsal (1MGD and 2MGD). Results: Following implantation surgery, extracellular recordings and triaxial inertial sensor data were collected from behaving Wistar rats (n=5). Results indicate that tetrodes in Au1 regions (1Au1: -0.483 ± 0.008, 2Au1: -0.618 ± 0.008), AuV (-0.618 ± 0.005), and AuD (-0.472 ± 0.007) exhibited signals with greater amplitudes compared to tetrodes in MGV (1MGV: -0.228 ± 0.006, 2MGV: -0.256 ± 0.004) and MGD (1MGD: -0.193 ± 0.008, 2MGD: -0.162 ± 0.004). Conclusions: These findings suggest that the developed tetrode array sensor may function as an electrophysiologically stable device for recording neural activity in the AuC and MGN of rats.