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Abstract
The fly visual system offers a unique opportunity to explore computations performed by single neurons. Two previous studies characterized, in vivo, the receptive field (RF) of the vertical system (VS) cells of the blowfly (calliphora vicina), both intracellularly in the axon, and, independently using Ca2+ imaging, in hundreds of distal dendritic branchlets. We integrated this information into detailed passive cable and compartmental models of 3D reconstructed VS cells. Within a given VS cell type, the transfer resistance (TR) from different branchlets to the axon differs substantially, suggesting that they contribute unequally to the shaping of the axonal RF. Weighting the local RFs of all dendritic branchlets by their respective TR yielded a faithful reproduction of the axonal RF. The model also predicted that the various dendritic branchlets are electrically decoupled from each other, thus acting as independent local functional subunits. The study suggests that single neurons in the fly visual system filter dendritic noise and compute the weighted average of their inputs.
Highlights
In the last few decades, detailed cable and compartmental models have been constructed for a variety of neuron types
We demonstrate that unequal weighting of dendritic branchlets as well as linear non-linear filtering are two functions that are likely to be implemented by the dendrites of vertical system (VS) cells and, interestingly, that the branchlets of VS cells operate as essentially independent local functional subunits with little interaction among them
The reconstruction of even a single branchlet’s receptive field is a tedious and prolonged process; this difficulty is further exacerbated by the limited lifetime of each sampled cell
Summary
In the last few decades, detailed cable and compartmental models have been constructed for a variety of neuron types. In a recent study[14], the view from the axon was complemented by a view from the dendrites of VS cells (see Methods and Fig. 1A) by performing Ca2+ imaging of multiple dendritic branchlets from a single VS cell (in case in point, thin distal branches, typically 4th order or above, as highlighted in red in Fig. 2B), while visual stimuli were presented Having both the dendritic and the axonal measurements at a single VS-cell provides a unique opportunity to explore the principles that govern the transformation of the cells’ multiple inputs to the axonal output, that is, the process in which the receptive fields of multiple dendritic branchlets are integrated to the axonal receptive field
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