Setting up a multi-electrode
array (MEA) to record from the chicken retina in vitro
The multi-electrode array (MEA) (see multichannelsystems)
is a powerful tool to study the electrical responses of tissues
in vitro.
Furthermore, recording while spatially resolved patterns are projected on the retina permits to study aspects of spatial processing, like spatial resolution, contrast sensitivity and contrast adaptation.
Developing the optics to stimulate the retina in the recording chamber with moving patterns
To stimulate the retina with moving or spatially
resolved patterns, a CRT display is imaged on the retina from below.
The CRT monitor content is controlled by the computer, and the stimuli were generated by custom-made software, written in Visual C++.
Fig. 1: Set-up to display focused and defocused patterns on the retina in vitro while the ganglion cell responses are recorded.
Effects of defocus on the responses of retinal ganglion cells
The major question here is whether ganglion cells can distinguish between a global drop in contrast, or defocus. To this end, phase-reversing checkerboards of various spatial frequencies were presented at different contrasts and the contrast sensitivity function of the recorded units were mapped. In a second experiment, the checkerboards were defocused by trial lenses
Fig. 2: Peri-event rasters of spikes recorded from selected channels of the MEA when a chicken retina was stimulated and different amounts of defocus were imposed (ordinate). The phase-reversal of the checkerboard occurred at time zero. The spikes reach their peak density at about 0.1 sec later but the delay and the spike rates were affected by defocus. At +/-3 D of defocus, the checkerboard was no longer resolved.
Optomotor-Analysis of contrast sensitivity and contrast adaptation in chickens and comparison to the in-vitro data
To be able to judge how representative the recordings of the in-vitro retina describe the function in vivo, some of the experiments above are currently studied in behavioural experiments.
Fig. 3: Head optomotor tracking in a little black chicken. Angular head position was tracked simply by two white paper spots attached to the chicken head.
