Electrophysiology of Natural and Artificial Vision - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 377

ERG

1500

Pre NMDA

1000

500

Post NMDA

0

Pre - Post

-500

-1000

-100 0 100 200 300 400 500 600 700 800

Time (ms)

40

eERG

Pre NMDA

30

20 Post NMDA

10

Pre - Post

0

-10

-20

-100 0 100 200 300 400 500 600 700 800

Time (ms)

Figure 20.7. ERG and eERG responses recorded in one experiment employing pharma-
cological dissection. ERG responses to light stimuli are plotted on the upper axes; eERG
responses to electrical stimulation are plotted on the lower axes. Waveforms are shifted
vertically for clarity; all pre-stimulus baselines have average values of zero. The top
trace in each panel was recorded under baseline conditions, and are typical ERG and
eERG response waveforms. The middle trace in each panel was recorded approximately
20 minutes following intravitreal injection of NMDA, which binds to third-order neurons.
Removing the corneal-negative contribution of third-order neurons enhances the b-wave
in the ERG (consistent with previous reports), and eliminates the N135 component of the
eERG. This strongly suggests that third-order neurons are responsible for the N135 eERG
response component. The bottom trace in each panel plots the difference waveform (pre-
NMDA minus post-NMDA), and isolates the portion of the baseline response removed
by the presence of the drug.

eration or to changes in electrode design or stimulus parameters can now be
studied.
The second objective of using pharmacological dissection described above
(identifying the direct targets of electrical stimulation) requires particular care