Biology Reference
In-Depth Information
6.2 Midget ganglion cells as synthesizers
Polyak's histological investigation had revealed that the retina of
primates had a very complex neural structure. This finding challenged
the validity of the basic presumptions of Schultze's (
1866
) and
Helmholtz's (
1896
) colour theories that the three different kinds
of colour-related processes were transmitted independently from
the photoreceptor to the brain, where eventually the integration
processing took place. Indeed, Polyak's investigation of the structural
details of the retina made evident that the ganglion cells were probably
as essential for the transformation of the centripetal dynamic visual
current as the bipolar cells. Thus, after passing through the bipolar
cells, the impulses generated in the photoreceptors were found to be
transmitted by
ive
different varieties of ganglion cells before they were
conveyed to the brain. Presuming that the bipolar cells were analyzers,
Polyak came to the conclusion that the synthesis and compounding
of the transmuted cone impulses, at least partially, were carried out
by the ganglion cells of the retina. Furthermore, by an examination
of the morphological features, especially the synaptic characteristics
of the different types of ganglion cells, Polyak found reason to believe
that only the midget ganglion cells could carry out the synthesis of
the three primary colour-related excitations into compound processes.
This was because of their relatively great number and small size, and
because only the midget ganglion cells were related to all varieties of
amacrine cells. He found additional evidence in support of his assump-
tion in psychophysical studies which showed that in the centre of the
field of vision, corresponding to the area of highest acuity, the smallest
discernible object could be seen in variously coloured lights rapidly
following one another, and also that it was impossible to observe two
different colours simultaneously at the same location.
6.3 The specific fibre-energy doctrine
questioned
Polyak concluded that each midget ganglion cell had the ability to
transmit to the brain the entire range of spectral colour-related impulses
