Subcellular mapping of dendritic activity in optic flow processing neurons

Dendritic integration is a fundamental element of neuronal
information processing. So far, few studies have provided a
detailed picture of this process, describing the properties of
local dendritic activity and its subcellular organization. Here, I
used 2-photon calcium imaging in optic flow processing neurons of
the blowfly Calliphora vicina to determine the preferred location
and direction of local motion cues for small branchlets throughout
the entire dendrite. I found a pronounced retinotopic mapping on
both the subcellular and the cell population level. In addition,
dendritic branchlets residing in different layers of the neuropil
were tuned to distinct directions of motion. Within one layer,
local preferred directions varied according to the deflections of
the ommatidial lattice. Summing the local receptive fields of all
dendritic branchlets reproduced the characteristic properties of
these neurons’ axonal output receptive fields. These results
corroborate the notion that the dendritic morphology of vertical
system cells allows them to selectively collect local motion inputs
with particular directional preferences from a spatially organized
input repertoire, thus forming filters that match global patterns
of optic flow. These data illustrate a highly structured circuit
organization as an efficient way to hard-wire a complex sensory
task.