Journal of Neuroscience, Vol 16, 769-784, Copyright © 1996 by Society for Neuroscience
Functional organization of a neural map in the cricket cercal sensory system
GA Jacobs and FE Theunissen
Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.
Directionally selective mechanosensory afferents in the cricket cercal
sensory system form a map of air current direction in the terminal
abdominal ganglion. The global organization of this map was revealed by
studying the anatomical relationships between an ensemble of sensory
afferents that represented the entire range of receptor hair directional
sensitivities on the sensory epithelium. The shapes and three-dimensional
positions of the terminal arborizations of these cells were highly
conserved across animals. Afferents with similar directional sensitivities
arborized near each other within the map, and their terminal arborizations
showed significant anatomical overlap. There was a clear global
organization pattern of afferents within the map: they were organized into
a spiral shape, with stimulus direction mapped continuously around the
spiral. These results demonstrate that this map is not formed via a direct
point-to-point topographic projection from the sensory epithelium to the
CNS. Rather, the continuous representation of air current direction is
synthesized within the CNS via an anatomical reorganization of the afferent
terminal arbors. The arbors are reorganized according to a functional
property that is independent of the location of the mechanoreceptor in the
epithelium. The ensemble data were used to derive predictions of the
patterns of steady-state excitation throughout the map for different
directional stimuli. These images represent quantitative and testable
predictions of functional characteristics of the entire neural map.
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