Eickenscheidt M, Jenkner M, Thewes R, Fromherz P, Zeck G. Electrical stimulation of retinal neurons in epiretinal and subretinal configuration using a multicapacitor array. J Neurophysiol 107: 2742-2755, 2012. First published February 22, 2012 doi:10.1152/jn.00909.2011.-Electrical stimulation of retinal neurons offers the possibility of partial restoration of visual function. Challenges in neuroprosthetic applications are the long-term stability of the metal-based devices and the physiological activation of retinal circuitry. In this study, we demonstrate electrical stimulation of different classes of retinal neurons with a multicapacitor array. The array-insulated by an inert oxideallows for safe stimulation with monophasic anodal or cathodal current pulses of low amplitude. Ex vivo rabbit retinas were interfaced in either epiretinal or subretinal configuration to the multicapacitor array. The evoked activity was recorded from ganglion cells that respond to light increments by an extracellular tungsten electrode. First, a monophasic epiretinal cathodal or a subretinal anodal current pulse evokes a complex burst of action potentials in ganglion cells. The first action potential occurs within 1 ms and is attributed to direct stimulation. Within the next milliseconds additional spikes are evoked through bipolar cell or photoreceptor depolarization, as confirmed by pharmacological blockers. Second, monophasic epiretinal anodal or subretinal cathodal currents elicit spikes in ganglion cells by hyperpolarization of photoreceptor terminals. These stimuli mimic the photoreceptor response to light increments. Third, the stimulation symmetry between current polarities (anodal/cathodal) and retina-array configuration (epi/sub) is confirmed in an experiment in which stimuli presented at different positions reveal the center-surround organization of the ganglion cell. A simple biophysical model that relies on voltage changes of cell terminals in the transretinal electric field above the stimulation capacitor explains our results. This study provides a comprehensive guide for efficient stimulation of different retinal neuronal classes with low-amplitude capacitive currents.
The low-frequency noise (LF-noise) of deep-submicrometer MOSFETs is experimentally studied with special emphasis on yield relevant parameter scattering. A novel modeling approach is developed which includes detailed consideration of statistical effects. The model is based on device physics parameters which cause statistical variations in LF-noise behavior of individual devices. Discrete quantities are used and analytical results for the statistical parameters are derived. Analytical equations for average value and standard deviation of noise power are provided. The model is compatible with standard compact models used for circuit simulation.
We report on the recording of electrical activity in cultured hippocampal slices by a multitransistor array (MTA) with 16,384 elements. Time-resolved imaging is achieved with a resolution of 7.8 microm on an area of 1 mm2 at 2 kHz. A read-out of fewer elements allows an enhanced time resolution. Individual transistor signals are caused by local evoked field potentials. They agree with micropipette measurements in amplitude and shape. The spatial continuity of the records provides time-resolved images of evoked field potentials and allows the detection of functional correlations over large distances. As examples, fast propagating waves of presynaptic action potentials are recorded as well as patterns of excitatory postsynaptic potentials across and along cornu ammonis.
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