Artificial Vision: Vision of a Newcomer - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 34

responses in the electroretinogram, and no evoked field potentials could be
recorded from the superior colliculus (SC) (the upper and the middle traces in
Figure 2.2b, respectively).
We first addressed the following issues: Can a focal STS to the retina with
degenerated photoreceptors excite the residual neurons, especially RGCs, and
can their excitation be transmitted via the optic nerve (ON) to the visual areas
of the brain?

(C)

ERG

20 uV

100 ms

VEP

100 uV

N1

100 ms

N2

EEP

20 ms

50 uV

P1

Figure 2.2. STS in normal and RCS rats. (a) A photomicrograph of a retinal section of
an adult RCS rat stained by hematoxylin-eosin. RGC: retinal ganglion cell, IPL: inner
plexiform layer, INL: inner nuclear layer. (b) A design of electrophysiological exper-
iment in rats. SE: suprachoroidal electrode (anode), VE: vitreous electrode (cathode).
(c) Neuronal responses evoked by flashing light and STS in a RCS rat. Upper trace:
electroretinogram (ERG) to flashing light stimulus, showing that the retina is unresponsive
to the light stimulus. Middle trace: Averaged visually evoked potentials (VEP) recorded
from the SC, also showing no reponse. Bottom trace, Averaged electrically evoked poten-
tials (EEP) to STS (10, 30, 60, 80, and 100A) recoded from the SC. (d) Differential
distribution of STS-evoked responses via two separated electrodes. Left: two crosses
indicate retinal positions of STS applied via a suprachoroidal elecrode, separated 1mm
from each other (SE1 and SE2). A filled circle indicates the ON head. D: dorsal,
T: temporal, V: ventral, N: nasal, Right: distribution of collicular EPs in response to a
single STS of 100A to SE1 (the lower), and SE2 (the upper). Recording of EPs was
done at every distance of 250m. Center and radius of each Circle indicate the recording
site of EPs and the relative amplitude of P1-N1 component, respectively. R: rostral, L:
lateral.