Multi-unit recordings in the stick insect Carausius morosus reveal distinct mechanosensory and olfactory activity patterns among antennal lobe neurons.

In the absence of light, the stick insect Carausius morosus relies on sensory modalities such as olfaction and mechanosensation instead of vision. Within the near-range environment, these insects use their long antennae to detect obstacles and gather tactile information, enabling them to grasp contacted objects with their front legs. However, for far-range orientation, they may integrate mechanosensory inputs with additional cues from non-contact modalities, including olfaction. Here we focus on olfactory processing in stick insects, aiming to establish the stick insect as a model to study both, near-range (tactile) and far-range (olfactory, wind, sound) sensory integration and their effects on motor control. As a first step, we established long-term multi-unit recordings of neurons in the primary olfactory neuropile, the antennal lobe (AL) to confirm general principles of odour processing in insects. Indeed, our recordings revealed that hexanal, i.e. the smell of freshly cut leaves, induced a distinct pattern of activity within the AL network, corresponding to its relevance to a herbivore and confirming the significance of the AL in extracting behaviourally relevant olfactory information. Furthermore, we discovered mechanically induced activity in AL neurons likely related to airborne vibration such as sound, highlighting that both olfactory and mechanical stimuli are processed within the AL, with a substantial fraction of neurons responsive to both modalities.