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a diffused light source. An extended source stimulates mnny neighboring receptors
which contribute to adaptation of the MC response. tauglin (1984) shows that this is
so in fly LMCS. The spatial response of MCs was not investigated in the present experi-
ments and should be inclu (i ed in f u t uë e research esmcialy sinœ no spatial antagonism
was found by Kien and Menzel (1977) in medula cels. .
The photoreceptors divide the light stimultls into three distinct signals (green,
blue and UV). The UV signal seems to be transmited directly to the medula tlrough
the long visual fibres, although according to Uibi (1981) the L1 monopolar cels also
receive synapses from the lvf's in the lamina, together with synapses from the greenand
blue-sensitive receptor axons. Also according to Uibi, the blue and green photoreceptor
axons synapse onto the 12 monopolars, whereas the 1.3 cels receive inputs
only from one type of photoreceptor, probably the green ones. 1.4 cells apparently
receive
no direct inputs from the rece' ptors but extend dendrites to neighboring
cartridges where they probably pick up inputs from the other MCs. How is this
anatomicaly deduced wiring diagram utilized by the MCs? Pooling of the responses
of several cells into one postsynaptic cel is often used as a strategy to improve the
signal to noise ratio and this seems to be the case in the bee as evidenced by the m uch
steeper V/log I functions of the LMCS compared to those of retinular cels.
Although spectral opponency might be expected from the 12 cels tl-augltlin,
1984). Only one instance was recorded in the unmarked cel mentioned above.
Therefore, with tlkis possible exception, no kind of color coding can be infered from
the responses recorded, and it must be concluded that this is either pe' rformed by
other cel types, not recorded from in these experiments, or in subsequent nelzropiles.
No opponency was found by Shaw (1981) in the lamina of Diptera either. It shoud
be noted that Kien & Menzel (1977) reported color opponent cels in the medula of
the bee.
The only clearly discernible function of the recorded MCs is that of highly
sensitive detectors of spatial or temporal contrast.
References:
Kien, J., Menzel, R. (1977). Cluomatic properties of interneurons in the optic lobes of the bee.
I - Broad band neurons; 11 - Narrow band and color opponent nelzrons-l. Comp. Physiol. 111 :
1 7-53 . .
Laughlin, S. ( 1984). The roles of parallel channels in early visual processing by the artlropod
compound eyc. In: M. A. Ali (ed.) Photoreception and Vision frl Inpertebrates. Plenum Press,
New York. . '
Laughlin, S., Hazdie, R.C. (1978). Com mon strategies for light adaptation in the peripheral visual
systems of fly and dragonfly. J. Comp. Physiol. 128 : 319-340.