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Caption : figure 1. voltammetric waveforms applied to the carbon-fiber to detect analytes electrochemically. (a) oxygen-sensitive waveform. currents generated from the reduction of oxygen are recorded at -1.30 to -1.35 v, before the switching potential. dopamine (da) is oxidized on the initial positive scan (+0.65 v), and then reduced on the reverse scan (-0.26 v). (b) a convolution-based method (cbm) waveform with heightened da sensitivity relative to the oxygen-sensitive waveform. the potential step preceding the triangle waveform enables the prediction and removal of non-faradaic interfering currents. dashed grey lines indicate oxidative and reductive peak potentials.

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Caption : figure 2. simultaneous electrochemical and electrophysiological dc potential recordings during sd waves using the oxygen-sensitive waveform. (a) color plot (top) recorded during a passing wave of sd with an epoxy-sealed electrode. extracted oxygen (o<sub>2</sub>) and dopamine (da) concentration traces from the color plot, and time-aligned dc potential trace (bottom). vertical dashed line indicates the sd event onset. (b) sd recorded at a non-epoxy electrode in a separate subject from a. color plot (top). o<sub>2</sub> and da concentration traces, and dc potential (bottom). (c) measured current response of an epoxy-sealed electrode to eight potential steps, 0 to 70 mv, δ 10 mv. (d)  same as c, but for a non-epoxy electrode. (e) left: plot of the plateau current obtained from c and d against the potential magnitude of the applied steps. epoxy electrode data in black. non-epoxy electrode data in grey. right: simplified diagram for electrical characteristics of carbon-fiber microelectrode seals. solution resistance, r<sub>soln</sub>; double-layer capacitance, c<sub>dl</sub>; leak resistance, r<sub>leak</sub>.

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Caption : figure 3. recordings on the oxygen-sensitive waveform during sd events in the nucleus accumbens. (a) representative color plot from consecutively elicited sd waves (n = 5). (b) concentration traces for dopamine (da) and oxygen (o<sub>2</sub>), at the da oxidation potential (+0.65 v) the oxygen reduction potential (-1.33 v), respectively. peak concentrations are 33.9 ± 1.1 µm oxygen and 6.0 ± 0.5 µm dopamine (n = 5).

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Caption : figure 4. characterization of fscv signals on the oxygen-sensitive waveform during a sd wave in the nucleus accumbens. (a) fscv color plot recorded during a spreading depression event. a pinprick was delivered at 0 s. the sd presented as a massive change in current at multiple potentials 115 s after the stimulus. white dashed lines indicate potentials of analyte oxidation or reduction, or interfering currents. (b) representative cyclic voltammogram collected during spreading depression event (t = 117 s, indicated by the dashed grey line in a and c). grey arrow heads indicate the direction of voltage scan. asterisks designate the oxidation and reduction potentials for dopamine (da); triangles denote the switching potential (sp) peaks; a star specifies the q-peak; a circle marks the reduction potential for oxygen. (c) currents extracted from the potentials indicated in a. the dashed line is repeated here for clarity.

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Caption : figure 5. time-varied background subtraction signals reveal characteristic dopamine (da) cyclic voltammogram (cv).  (a) current traces from data in figure 3. black, dotted line at 117 s indicates time of maximum current signal during sd wave.  the grey, dashed line at 90 s designates a time before the wave of sd as a quiescent baseline. the grey, dashed line at 140 s denotes a time during the sd wave where the current for da oxidation has significantly decayed, but the current at the 1<sup>st</sup> sp and q-peak potentials are at near max.  (b) cvs taken at 117 s, indicated by the black, dotted line in a. setting the background signal for subtraction at 90 s generates the grey cv.  shifting the background signal time to 140 s generates the black cv.

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Caption : figure 6. convolution-based method to enhance dopamine (da) signal specificity. (a) color plot of a sd wave in the nac obtained using the convolution-based method waveform. (b) same color plot following subtraction of convolution-based predictions of non-faradaic current with in-house labview software. (c) cvs obtained from the color plots before (grey, from a) and after (black, from b) removal of non-faradaic currents. (d) da concentration traces obtained at +0.65 v on positive scan, from a (grey) and b (black).

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Caption : figure 7. sequential oxygen concentration traces (mean ± sem) obtained with fscv (black) and amperometry (blue) in the same subject. concentrations were obtained by using the respective calibration factors for each technique.