Abstract
Studying the insect visual system provides important data on
the basic neural mechanisms underlying visual processing. As
in vertebrates, the first step in visual processing in insects
is through a series of retinotopic neurons. Recent studies on
flies have found that these converge onto assemblies of
columnar neurons in the lobula, the axons of which segregate
to project to discrete optic glomeruli in the lateral
protocerebrum. This arrangement is much like the fly's
olfactory system, in which afferents target uniquely
identifiable olfactory glomeruli. Here, whole-cell patch
recordings show that even though visual primitives are
unreliably encoded by single lobula output neurons because of
high synaptic noise, they are reliably encoded by the ensemble
of outputs. At a glomerulus, local interneurons reliably code
visual primitives, as do projection neurons conveying
information centrally from the glomerulus. These observations
demonstrate that in Drosophila, as in other dipterans, optic
glomeruli are involved in further reconstructing the fly's
visual world. Optic glomeruli and antennal lobe glomeruli
share the same ancestral anatomical and functional ground
pattern, enabling reliable responses to be extracted from
converging sensory inputs.
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