RT Journal Article SR Electronic T1 Two compasses in the central complex of the locust brain JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 0940-18 DO 10.1523/JNEUROSCI.0940-18.2019 A1 Uta Pegel A1 Keram Pfeiffer A1 Frederick Zittrell A1 Christine Scholtyssek A1 Uwe Homberg YR 2019 UL http://www.jneurosci.org/content/early/2019/02/12/JNEUROSCI.0940-18.2019.abstract AB Many migratory insects rely on a celestial compass for spatial orientation. Several features of the daytime sky, all generated by the sun, can be exploited for navigation. Two of these are the position of the sun and the pattern of polarized skylight. Neurons of the central complex (CX), a group of neuropils in the central brain of insects, have been shown to encode sky compass cues. In desert locusts the CX holds a topographic, compass-like representation of the plane of polarized light (E-vector), presented from dorsal direction. In addition, these neurons also encode the azimuth of an unpolarized light spot, likely representing the sun. Here we investigate whether, in addition to E-vector orientation, the solar azimuth is represented topographically in the CX. We recorded intracellularly from 8 types of CX neuron, while stimulating animals of either sex with polarized blue light from zenithal direction and an unpolarized green light spot, rotating around the animal's head at different elevations. CX neurons did not code for elevation of the unpolarized light spot. However, two types of columnar neuron showed a linear correlation between innervated slice in the CX and azimuth tuning to the unpolarized green light spot, consistent with an internal compass representation of solar azimuth. Columnar outputs of the CX also showed a topographic representation of zenithal E-vector orientation but the two compasses were not linked to each other. Combined stimulation with unpolarized green and polarized blue light suggest that the two compasses interact in a non-linear way.SIGNIFICANCE STATEMENTIn the brain of the desert locust, neurons sensitive to the plane of celestial polarization are arranged like a compass in the slices of the central complex. These neurons, in addition, code for the horizontal direction of an unpolarized light cue possibly representing the sun. We show here that horizontal directions are, in addition to E-vector orientations from dorsal direction, represented in a compass-like manner across the slices of the central complex. However, both compasses are not linked to each other but seem to interact in a cell specific non-linear way. Our study confirms the role of the central complex in signaling heading directions and shows that different cues are employed for this task.