Closed-Loop Characterization of Neuronal Activation Using Electrical Stimulation and Optical Imaging

• Main Authors: Michelle L. Kuykendal, Gareth S. Guvanasen, Steve M. Potter, Martha A. Grover, Stephen P. DeWeerth
• Format: Article
• Language: English
• Published: MDPI AG 2017-06-01
• Series: Processes
• Subjects: extracellular electrical stimulation; closed-loop; strength-duration; micro-electrode array (MEA); dissociated culture; activation curve; optical recording
• Online Access: http://www.mdpi.com/2227-9717/5/2/30

We have developed a closed-loop, high-throughput system that applies electrical stimulation and optical recording to facilitate the rapid characterization of extracellular, stimulus-evoked neuronal activity. In our system, a microelectrode array delivers current pulses to a dissociated neuronal culture treated with a calcium-sensitive fluorescent dye; automated real-time image processing of high-speed digital video identifies the neuronal response; and an optimized search routine alters the applied stimulus to achieve a targeted response. Action potentials are detected by measuring the post-stimulus, calcium-sensitive fluorescence at the neuronal somata. The system controller performs directed searches within the strength–duration (SD) stimulus-parameter space to build probabilistic neuronal activation curves. This closed-loop system reduces the number of stimuli needed to estimate the activation curves when compared to the more commonly used open-loop approach. This reduction allows the closed-loop system to probe the stimulus regions of interest in the multi-parameter waveform space with increased resolution. A sigmoid model was fit to the stimulus-evoked activation data in both current (strength) and pulse width (duration) parameter slices through the waveform space. The two-dimensional analysis results in a set of probability isoclines corresponding to each neuron–electrode pair. An SD threshold model was then fit to the isocline data. We demonstrate that a closed-loop methodology applied to our imaging and micro-stimulation system enables the study of neuronal excitation across a large parameter space.