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ItemFocal Activation of Primary Visual Cortex Following Supra-choroidal Electrical Stimulation of the Retina: Intrinsic Signal Imaging and Linear Model AnalysisCloherty, SL ; Hietanen, MA ; Suaning, GJ ; Ibbotson, MR (IEEE, 2010-01-01)We performed optical intrinsic signal imaging of cat primary visual cortex (Area 17 and 18) while delivering bipolar electrical stimulation to the retina by way of a supra-choroidal electrode array. Using a general linear model (GLM) analysis we identified statistically significant (p < 0.01) activation in a localized region of cortex following supra-threshold electrical stimulation at a single retinal locus. OUR RESULTS: (1) demonstrate that intrinsic signal imaging combined with linear model analysis provides a powerful tool for assessing cortical responses to prosthetic stimulation, and (2) confirm that supra-choroidal electrical stimulation can achieve localized activation of the cortex consistent with focal activation of the retina.
ItemEpiretinal Electrical Stimulation and the Inner Limiting Membrane in Rat RetinaCloherty, SL ; Wong, RCS ; Hadjinicolaou, AE ; Meffin, H ; Ibbotson, MR ; O'Brien, BJ (IEEE, 2012-01-01)In this paper we aim to quantify the effect of the inner limiting membrane (ILM) of the retina on the thresholds for epiretinal electrical stimulation of retinal ganglion cells by a microelectronic retinal prosthesis. A pair of bipolar stimulating electrodes was placed either above (on the epiretinal surface) or below the ILM while we made whole-cell patch-clamp recordings from retinal ganglion cells in an isolated rat retinal whole-mount preparation. Across our cell population we found no significant difference in the median threshold stimulus amplitudes when the stimulating electrodes were placed below as opposed to above the ILM (p = 0.08). However, threshold stimulus amplitudes did tend to be lower when the stimulating electrodes were placed below the ILM (30 µA vs 56 µA).
ItemRetinal ganglion cells electrophysiology: the effect of cell morphology on impulse waveformMaturana, MI ; Wong, R ; Cloherty, SL ; Ibbotson, MR ; Hadjinicolaou, AE ; Grayden, DB ; Burkitt, AN ; Meffin, H ; O'Brien, BJ ; Kameneva, T (IEEE, 2013-01-01)There are 16 morphologically defined classes of rats retinal ganglion cells (RGCs). Using computer simulation of a realistic anatomically correct A1 mouse RGC, we investigate the effect of the cell's morphology on its impulse waveform, using the first-, and second-order time derivatives as well as the phase plot features. Using whole cell patch clamp recordings, we recorded the impulse waveform for each of the rat RGCs types. While we found some clear differences in many features of the impulse waveforms for A2 and B2 cells compared to other cell classes, many cell types did not show clear differences.