Neurons of the central complex of the locust Schistocerca gregaria are sensitive to polarized light.

The central complex is a topographically ordered neuropil structure in the center of the insect brain. It consists of three major subdivisions, the upper and lower divisions of the central body and the protocerebral bridge. To further characterize the role of this brain structure, we have recorded the responses of identified neurons of the central complex of the desert locust Schistocerca gregaria to visual stimuli. We report that particular types of central complex interneurons are sensitive to polarized light. Neurons showed tonic responses to linearly polarized light with spike discharge frequencies depending on e-vector orientation. For all neurons tested, e-vector response curves showed polarization opponency. Receptive fields of the recorded neurons were in the dorsal field of view with some neurons receiving input from both compound eyes and others, only from the ipsilateral eye. In addition to responses to polarized light, certain neurons showed tonic spike discharges to unpolarized light. Most polarization-sensitive neurons were associated with the lower division of the central body, but one type of neuron with arborizations in the upper division of the central body was also polarization-sensitive. Visual pathways signaling polarized light information to the central complex include projections via the anterior optic tubercle. Considering the receptive fields of the neurons and the biological significance of polarized light in insects, the central complex might serve a function in sky compass-mediated spatial navigation of the animals.