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Fig. 2. Anatomical prediction of synaptic connectivity between filiform sensory
afferents and interneurons. (A) A reconstruction of interneuron right (R)10-2
is shown in yellow. Afferent arbors from 12 different filiform hair receptors
are shown in other colors. The color of each afferent corresponds to its
direction of peak activation. These 12 classes span the range of all different
classes of receptor directional sensitivities. Inset cartoon shows the color
code indicating the preferred stimulus direction with respect to the cricket
body coordinates. (B) Composite view (saggital) of 11 different sensory
afferents from the left cercus illustrating the continuous representation of
direction selectivity within the nervous system. Cells with similar
directional tuning arborize near each other and those tuned to other
directions are spatially segregated showing their color. (C) Image of the
afferent map of air current direction, from both cerci, with an image of the
compartmental model of interneuron 10-2 imbedded in the map. Each directional
class of afferent arbors is transformed into a `statistical cloud'
corresponding to the density of synaptic terminals for that stimulus
direction. This provides a direct demonstration of the neural map of
direction. The overlap between the sensory interneuron with the afferent map
of air current direction predicts synaptic connectivity from the afferents
onto that interneuron. Here we just mask the interneuron dendrites with the
color corresponding to the statistical cloud of afferent synapses in that
region. (D) Image of the distribution of synaptic varicosities of the
population of sensory afferents from the left cercus tuned to different air
current directions from the left cercus. Same view as in B. The varicosities
form a continuous three-dimensional structure in the neuropil. Note that the
peak directional tuning of the varicosities changes continuously with location
around the structure. Starting at the top of the structure (pink) and moving
clockwise [red, yellow (out of view), green and blue].
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