A low-cost, multiplexed µECoG system for high-density recordings in freely moving rodents.

OBJECTIVE: Micro-electrocorticography (µECoG) offers a minimally invasive neural interface with high spatial resolution over large areas of cortex. However, electrode arrays with many contacts that are individually wired to external recording systems are cumbersome and make recordings in freely behaving rodents challenging. We report a novel high-density 60-electrode system for µECoG recording in freely moving rats. APPROACH: Multiplexed headstages overcome the problem of wiring complexity by combining signals from many electrodes to a smaller number of connections. We have developed a low-cost, multiplexed recording system with 60 contacts at 406 µm spacing. We characterized the quality of the electrode signals using multiple metrics that tracked spatial variation, evoked-response detectability, and decoding value. Performance of the system was validated both in anesthetized animals and freely moving awake animals. MAIN RESULTS: We recorded µECoG signals over the primary auditory cortex, measuring responses to acoustic stimuli across all channels. Single-trial responses had high signal-to-noise ratios (SNR) (up to 25 dB under anesthesia), and were used to rapidly measure network topography within ∼10 s by constructing all single-channel receptive fields in parallel. We characterized evoked potential amplitudes and spatial correlations across the array in the anesthetized and awake animals. Recording quality in awake animals was stable for at least 30 days. Finally, we used these responses to accurately decode auditory stimuli on single trials. SIGNIFICANCE: This study introduces (1) a µECoG recording system based on practical hardware design and (2) a rigorous analytical method for characterizing the signal characteristics of µECoG electrode arrays. This methodology can be applied to evaluate the fidelity and lifetime of any µECoG electrode array. Our µECoG-based recording system is accessible and will be useful for studies of perception and decision-making in rodents, particularly over the entire time course of behavioral training and learning.

A low-cost, multiplexed electrophysiology system for chronic µECoG recordings in rodents.

Micro-Electrocorticography (µECoG) offers a minimally invasive, high resolution interface with large areas of cortex. However, large arrays of electrodes with many contacts that are individually wired to external recording systems are cumbersome and make chronic recording in freely behaving small animals challenging. Multiplexed headstages overcome this limitation by combining the signals from many electrodes to a smaller number of connections directly on the animal's head. Commercially available multiplexed headstages provide high performance integrated amplification, multiplexing and analog to digital conversion. However, the cost of these systems can be prohibitive for small labs or for experiments that require a large number of animals to be continuously recorded at the same time. Here we have developed a multiplexed 60-channel headstage amplifier optimized to chronically record electrophysiological signals from high-density µECoG electrode arrays. A single, ultraflexible (2 mm thickness) microHDMI cable provided the data interface. Using low cost components, we have reduced the cost of the multiplexed headstage to ~$125. Paired with a custom interface printed circuit board (PCB) and a general purpose data acquisition system (M-series DAQ, National Instruments), an inexpensive and customizable electrophysiology system is assembled. Open source LabVIEW software that we have previously released controlled the system. It can also be used with other open source neural data acquisition packages. Combined, we have presented a scalable, low-cost platform for high-channel count electrophysiology.