Biomedical Engineering Reference
In-Depth Information
1
Electrical Stimulation of Mammalian
Retinal Ganglion Cells Using Dense
Arrays of Small-Diameter Electrodes
Chris Sekirnjak
1
, Pawel Hottowy
2
, Alexander Sher
3
, Wladyslaw
Dabrowski
2
, Alan M. Litke
3
and E. J. Chichilnisky
1
1
The Salk Institute for Biological Studies
2
Faculty of Physics and Applied Computer Science, AGH University of Science
and Technology
3
Santa Cruz Institute for Particle Physics, University of California
Abstract:
Current epiretinal implants containa small number of electrodeswithdiameters
of a few hundred microns. Smaller electrodes are desirable to increase the
spatial resolutionof artificial sight. To lay the foundation for thenext generation
of retinal prostheses, we assessed the stimulation efficacy of micro-fabricated
arrays of 61 platinum disk electrodes with diameters 8-12m, spaced 60m
apart. Isolated pieces of rat, guinea pig, and monkey retina were placed on
the multi-electrode array ganglion cell side down and stimulated through
individual electrodes with biphasic, charge-balanced current pulses. Spike
responses from retinal ganglion cells were recorded either from the same or a
neighboring electrode.Most pulses evoked only 1-2 spikeswith short latencies
(0.3-10ms), and rarely was more than one recorded ganglion cell stimulated.
Threshold charge densities for eliciting spikes in ganglion cells were typically
below015mC/cm
2
for pulse durations between 50 and 200s, corresponding
to charge thresholds of
∼
100 pC. Stimulation remained effective after several
hours and at frequencies up to 100 Hz. Application of cadmium chloride
did not abolish evoked spikes, implying direct activation. Thus, electrical
stimulation of mammalian retina with small-diameter electrodes is achievable,
providing high temporal and spatial precision with low charge densities.
Introduction
Electrical stimulation of retinas in blind people has demonstrated the potential
for direct excitation of retinal neurons as a means of re-establishing
sight [1]. The retina in patients with advanced neurodegenerative diseases
333
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