A low-cost, scalable, current-sensing digital headstage for high channel countμECoG

Abstract

Objective High channel count electrode arrays allow for the monitoring of large-scale neural activity at high spatial resolution. Implantable arrays featuring many recording sites require compact, high bandwidth front-end electronics. In the present study, we investigated the use of a small, light weight, and low cost digital current-sensing integrated circuit for acquiring cortical surface signals from a 61-channel micro-electrocorticographic (μECoG) array. Approach We recorded both acute and chronic μECoG signal from rat auditory cortex using our novel digital current-sensing headstage. For direct comparison, separate recordings were made in the same anesthetized preparations using an analog voltage headstage. A model of electrode impedance explained the transformation between current- and voltage-sensed signals, and was used to reconstruct cortical potential. We evaluated the digital headstage using several metrics of the baseline and response signals. Main results The digital current headstage recorded neural signal with similar spatiotemporal statistics and auditory frequency tuning compared to the voltage signal. The signal-to-noise ratio of auditory evoked responses (AERs) was significantly stronger in the current signal. Stimulus decoding based on true and reconstructed voltage signals were not significantly different. Recordings from an implanted system showed AERs that were detectable and decodable for 52 days. The reconstruction filter mitigated the thermal current noise of the electrode impedance and enhanced overall SNR. Significance We developed and validated a novel approach to headstage acquisition that used current-input circuits to independently digitize 61 channels of μECoG measurements of the cortical field. These low-cost circuits, intended to measure photo-currents in digital imaging, not only provided a signal representing the local cortical field with virtually the same sensitivity and specificity as a traditional voltage headstage but also resulted in a small, light headstage that can easily be scaled to record from hundreds of channels.

Sub-millimeter ECoG pitch in human enables higher fidelity cognitive neural state estimation

“…Modeling and experimental analyses were performed to determine if and when higher density grids outperform lower density grids. An illustrative model with properties motivated from previous studies (Insanally et al, 2016;Kellis et al, 2016;Muller et al, 2016b;Trumpis et al, 2017) was developed to determine under what conditions a higher density grid might outperform a lower density grid. Analytical results for the simple 2-channel case and numerical results for higher dimensional cases are presented (Fig.…”

“…In fact, researchers in related work have used the Mahalanobis distance to score "evoked signal-to-noise ratio" in trials indicating that these assumptions are reasonable (Insanally et al, 2016;Trumpis et al, 2017).…”

“…We will assume only the preferred stimuli has signal. Previous studies have shown that correlation between raw channels measurements and features derived from various frequency bands can fit reasonably well to an exponential decay (Insanally et al, 2016;Kellis et al, 2016;Muller et al, 2016b;Trumpis et al, 2017). This motivated defining the signal to decay exponentially with respect to Euclidean distance from the peak activation site.…”

“…Previous simulation and empirical studies have used spatial spectral techniques to estimate the ideal spacing to be 1.25 mm (Freeman et al, 2000;Slutzky et al, 2010). Other empirical works have quantified spatial characteristics by using similarity metrics such as channel correlation vs channel distance (Chang, 2015;Insanally et al, 2016;Kellis et al, 2016;Muller et al, 2016b;Trumpis et al, 2017) with the interpretation that steeper falloffs indicate that high density grids are advantageous. However, a well-defined functional interpretation of these falloff curves has not been established.…”

“…In human studies of sub-millimeter pitch ECoG grids, recorded signals are evaluated using measures of electrophysiological signal similarity (e.g. correlation, coherence) (Insanally et al, 2016;Kellis et al, 2016;Muller et al, 2016b;Trumpis et al, 2017). While these measures provide insight into potential utility of higher density recordings, they do not provide a direct connection into the potential of higher spatial resolution devices to more accurately estimate neural state.…”