Visual responsiveness of central-complex neurons in the desert locust Schistocerca gregaria

Abstract

Event Abstract Back to Event Visual responsiveness of central-complex neurons in the desert locust Schistocerca gregaria Tobias Bockhorst1*, Ronny Rosner1 and Uwe Homberg1 1 Philipps-University Marburg, Biology, Germany The central complex is a set of midline-spanning neuropils in the insect brain playing an increasingly apparent role in motor control and visual integration, particularly visual object discrimination, visual place learning, and spatial orientation (1-4). In the desert locust, central-complex neurons were shown to represent the electric field vector of polarized light in a polarotopic gradient which may act as a sky compass for navigation during long-distance migrations (5,6). We performed intracellular recordings with subsequent tracer injections to measure the responsiveness of polarization-sensitive and other identified central-complex neurons to a variety of unpolarized light signals displayed in the left medio-lateral visual field. Flashes of different spectral composition served to test general light sensitivity while a variety of object-like light patterns was used to screen for more complex spatio-temporal tuning. Patterns most frequently presented comprise white or black bars varied in length and edge orientation, displayed either stationary or translating. The trajectory of translating bars and its relation to edge orientation were altered as well. In central-complex neurons hitherto encountered, stimulus correlated changes in spiking pattern ranged from stereotypical light responses to more complex and subtle modulations that appeared indicative of movement sensitivity or tuning to object positions. Additional data and further analysis is required to assess the consistency of these putative responses as well as their distance to occasionally complex background activity. In contrast, complementary recordings from optic-lobe- and descending neurons invading the medial protocerebrum showed substantially stronger and more reliable responses which confirms that these stimuli are generally adequate for the locust visual system and might be of behavioral significance. It remains to be shown whether central-complex neurons are involved in processing visual stimuli as applied in the present account or largely bypassed to establish more direct pathways for mediating fast behavioral responses.