Abstract
Same-electrode stimulation and recording with high spatial resolution, signal quality, and power efficiency is highly desirable in neuroscience and neural engineering. High spatial resolution and signal-to-noise ratio is necessary for obtaining unitary activities and delivering focal stimulations. Power efficiency is critical for battery-operated implantable neural interfaces. This study demonstrates the capability of recording single units as well as evoked potentials in response to a wide range of electrochemically safe stimulation pulses through high-resolution microelectrodes coated with co-deposition of Pt-Ir. It also compares signal-to-noise ratio, single unit activity, and power efficiencies between Pt-Ir coated and uncoated microelectrodes. To enable stimulation and recording with the same microelectrodes, microelectrode arrays were treated with electrodeposited platinum-iridium coating (EPIC) and tested in the CA1 cell body layer of rat hippocampi. The electrodes’ ability to (1) inject a large range of electrochemically reversable stimulation pulses to the tissue, and (2) record evoked potentials and single unit activities were quantitively assessed over an acute time period. Compared to uncoated electrodes, EPIC electrodes recorded signals with higher signal-to-noise ratios (coated: 9.77 ± 1.95 dB; uncoated: 1.95 ± 0.40 dB) and generated lower voltages (coated: 100 mV; uncoated: 650 mV) for a given stimulus (5 μA). The improved performance corresponded to lower energy consumptions and electrochemically safe stimulation above 5 μA (>0.38 mC/cm2), which enabled elicitation of field excitatory post synaptic potentials and population spikes. Spontaneous single unit activities were also modulated by varying stimulation intensities and monitored through the same electrodes. This work represents an example of stimulation and recording single unit activities from the same microelectrode, which provides a powerful tool for monitoring and manipulating neural circuits at the single neuron level.
Highlights
Recording from single neurons and stimulation to same microelectrodes near simultaneously is highly desirable for both basic neuroscience research and neural engineering applications
In addition to in vivo electrochemical characterization, we acutely evaluated and compared the ability of electrodeposited platinum-iridium coating (EPIC) coated and uncoated microelectrodes to bidirectionally stimulate to and record single units through the same microelectrode using an 8-channel microelectrode array implanted in the hippocampus with approximately every other electrode coated and the other half uncoated
Our results demonstrated that EPIC coating enabled electrochemically safe stimulation above 5 μA (>0.38 mC/cm2), which enabled recordings of spontaneous spikes, field excitatory post synaptic potentials, and population spikes (PSs) from both the stimulation electrode and neighboring recording electrodes
Summary
Recording from single neurons and stimulation to same microelectrodes near simultaneously is highly desirable for both basic neuroscience research and neural engineering applications. In other words, reducing electrode size for high spatial resolution stimulation and recording generally results in an increase of the electrochemical impedance of the electrode-tissue interface (Cogan, 2008) and higher thermal noise (Suner et al, 2005). There are three approaches used to make IrOx coated microelectrodes: activated iridium oxide film where a bulk iridium electrode is oxidized by cycling it through positive and negative voltages in an aqueous solution (Beebe and Rose, 1988), sputtered iridium oxide films, where an iridium target is used in the presence of oxygen (Cogan et al, 2004b, 2009), and electrodeposited iridium oxide (Lu et al, 2009) These techniques roughen the surface, increasing the capacitance as well. EPIC provides a powerful tool for monitoring and manipulating neural circuits at the single neuron level
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