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Sunday, July 19 • 9:00pm - 10:00pm
P92: Modelling the responses of ON and OFF retinal ganglion cells to infrared neural stimulation

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James Begeng, Wei Tong, Michael R Ibbotson, Paul Stoddart, Tatiana Kameneva

Backup link (since the one below seems to be broken): https://swinburne.zoom.us/j/93169734624

Email me at jbegeng@swin.edu.au if you have difficulty connecting, or if you can't make this timeslot.

Retinal degenerative diseases such as retinitis pigmentosa and age-related macular degeneration cause progressive photoreceptor loss leading to partial or total patient blindness. Retinal prostheses attempt to obviate this loss of photoreceptors by direct stimulation of the underlying retinal ganglion cell (RGC) circuitry, and are capable of restoring limited visual sensation to blind patients. Because these devices typically inject current through implanted electrode arrays, their spatial resolution is significantly limited, and their capacity for selective stimulation of distinct RGC types has not yet been established. In particular, selective stimulation of ON and OFF RGCs (which exhibit opposite light responses in vivo) constitutes a long- standing open problem in retinal prosthesis design.

Infrared neural modulation (INM) uses pulsed infrared light to deliver sharp thermal transients to neural tissue, and is capable of both neural stimulation and inhibition with a high spatial precision. This technique relies on at least two distinct mechanisms: a temperature gradient dependent capacitive current, and thermosensitive activation of the TRPV ion channels. For retinal prostheses, this high stimulus resolution offers an attractive alternative to the low resolution of current electrical prostheses; however, it is unclear how infrared-evoked currents may vary between the wide variety of RGC types in mammalian retina, or whether these differences may be harnessed for selective stimulation.

In this study, a single-compartment Hodgkin-Huxley-type model was simulated in a NEURON environment. The model included leak, sodium, potassium, calcium and low voltage activated calcium currents based on published data [1,2]. Thermally-evoked currents were simulated by a dT/dt dependent capacitive current based on GCS theory of bilayer capacitance [3].

Our results show that INM responses differ between ON and OFF RGCs. In particular, OFF cells have a prolonged depolarisation in response to millisecond timescale heat pulses, whilst ON cells exhibit a short depolarisation with a larger post-pulse hyperpolarisation. This difference is mainly due to the low voltage activated calcium current that is present in OFF and absent in ON RGCs. This prediction is yet to be confirmed experimentally, but may have important implications for the development of infrared retinal prostheses.


Old link, do not use: https://swinburne.zoom.us/j/91916507848?pwd=L1dqaVZwNkEvd21MU2UvalREeFVUQT09 Password: 930274

References

[1] Fohlmeister, J. F., & Miller, R. F. (1997a). Impulse encoding menchanisms of ganglion cells in the tiger salamander retina. Journal of Neurophysiology, 78, 1935–1947.

[2] Wang, X.-J., Rinzel, J., & Rogawski, M. (1991). A model of the T-type calcium current and the low-threshold spike in thalamic neurons. Journal of Neurophysiology, 66, 839–850.

[3] Eom, K., Byun, K.B., Jun, S.B., Kim, S.J., Lee, J. (2018) Theoretical Study on Gold-Nanorod-Enhanced Near-Infrared Neural Stimulation. Biophysical Journal, 115, 1481–1497

Speakers
JB

James Begeng

Faculty of Science, Engineering and Technology, Swinburne University of Technology



Sunday July 19, 2020 9:00pm - 10:00pm CEST
Slot 05