Volume 16, Number 15,
Issue of August 1, 1996
pp. 4551-4562
Copyright ©1996 Society for Neuroscience
Visual Motion-Detection Circuits in Flies: Parallel Direction-
and Non-Direction-Sensitive Pathways between the Medulla and Lobula
Plate
Received March 13, 1996; revised May 8, 1996; accepted May 9, 1996.
John K. Douglass and
Nicholas J. Strausfeld
Arizona Research Laboratories, Division of Neurobiology, University
of Arizona, Tucson, Arizona
The neural circuitry of motion processing in insects, as in
primates, involves the segregation of different types of visual
information into parallel retinotopic pathways that subsequently are
reunited at higher levels. In insects, achromatic, motion-sensitive
pathways to the lobula plate are separated from color-processing
pathways to the lobula. Further parallel subdivisions of the
retinotopic pathways to the lobula plate have been suggested from
anatomical observations. Here, we provide direct physiological evidence
that the two most prominent of these latter pathways are, indeed,
functionally distinct: recordings from the retinotopic pathway defined
by small-field bushy T-cells (T4) demonstrate only weak directional
selectivity to motion, in striking contrast with previously
demonstrated strong directional selectivity in the second, T5-cell,
pathway. Additional intracellular recordings and anatomical
descriptions have been obtained from other identified neurons that may
be crucial in early motion detection and processing: a deep medulla
amacrine cell that seems well suited to provide the lateral
interactions among retinotopic elements required for motion detection;
a unique class of Y-cells that provide small-field, directionally
selective feedback from the lobula plate to the medulla; and a new
heterolateral lobula plate tangential cell that collates directional,
motion-sensitive inputs. These results add important new elements to
the set of identified neurons that process motion information. The
results suggest specific hypotheses regarding the neuronal substrates
for motion-processing circuitry and corroborate behavioral studies in
bees that predict distinct pathways for directional and nondirectional
motion.
Key words:
insects;
vision;
parallel pathways;
motion
processing;
bushy T-cells;
motion computation