Distributed representation of social odors indicates parallel processing in 1 the antennal lobe of ants 2 3

23 In colonies of eusocial Hymenoptera cooperation is organized through social odors, and 24 particularly ants rely on a sophisticated odor communication system. Neuronal information 25 about odors is represented in spatial activity-patterns in the primary olfactory neuropile of the 26 insect brain, the antennal lobe (AL), which is analog to the vertebrate olfactory bulb. The 27 olfactory system is characterized by neuroanatomical compartmentalization, yet the functional 28 significance of this organization is unclear. Using two-photon calcium imaging, we 29 investigated the neuronal representation of multi-component colony odors, which the ants 30 assess to discriminate friends (nestmates) from foes (non-nestmates). In the carpenter ant 31 Camponotus floridanus, colony odors elicited spatial activity patterns distributed across 32 different AL compartments. Activity patterns in response to nestmate and non-nestmate 33 colony odors were overlapping. This was expected since both consist of the same components 34 at differing ratios. Colony odors change over time and the nervous system has to constantly 35 adjust for this (template reformation). Measured activity patterns were variable, and 36 variability was higher in response to repeated nestmate than to repeated non-nestmate colony 37 odor stimulation. Variable activity patterns may indicate neuronal plasticity within the 38 olfactory system, which is necessary for template reformation. Our results indicate that 39 information about colony odors is processed in parallel in different neuroanatomical 40 compartments, using the computational power of the whole AL network. Parallel processing 41 might be advantageous, allowing reliable discrimination of highly complex social odors. 42 43