Py. Burgi et Nm. Grzywacz, A BIOPHYSICAL MODEL FOR THE DEVELOPMENTAL TIME-COURSE OF RETINAL ORIENTATION SELECTIVITY, Vision research (Oxford), 38(18), 1998, pp. 2787-2800
A quantitative study of the time course of development of the percenta
ge of orientationally selective and isotropic ganglion cells in turtle
retina has recently been performed. This study revealed that as soon
as ganglion cells start responding to light, a large percentage of the
m are selective to the orientations of moving visual stimuli. This per
centage decreases with age to reach a minimum around hatching, increas
es dramatically after birth and finally, decreases again following the
first month of life to reach adult level. Concomitantly, the percenta
ge of cells responding isotropically to the orientation of elongated s
timuli increases monotonically until about 30 days after birth, stabil
izing afterwards. To account for both time courses, we propose a bioph
ysical model implementing features ubiquitous to developing vertebrate
retinas. These features include early dendritic and synaptic spatial
polarization, dendritic growth, and waves of activity generated sponta
neously or by visual stimulation sweeping across the inner plexiform l
ayer (IPL). The model also assumes a physiologically plausible Hebbian
rule, which includes long-term potentiation and depression. Computer
simulations of this model yield good fits of the data. The quality of
these fits confirms and extends results from an earlier model using co
mputationally-simple mechanisms, which suggested that early dendritic
polarization might be the seed for mature orientation selectivity. (C)
1998 Published by Elsevier Science Ltd. All rights reserved.