Speaker
Description
While the role of the antennal lobe (AL) in processing olfactory signals is well-documented, its function in integrating multiple sensory modalities remains underexplored. In addition to olfactory processing there is increasing evidence in mammals and insects that mechanical stimuli are also processed within the olfactory pathway at an early processing level, indicating a close connection between both modalities. When we established multi-unit recordings in the AL of stick insects C. morosus, we observed the same phenomenon: subpopulations of the recorded AL projection neurons responded either to mechanosensory stimuli (14.4%), olfactory stimuli (11.9%), or both modalities (69.5%). Before investigating cross modal effects in neural coding within the AL, we aim to understand the features encoded within these mechanical responses. By applying acoustic vibrations with power spectra that differed primarily in three frequencies (265Hz, 600Hz and 900Hz), which we applied in three varying amplitudes, we analysed the effect of stimulus frequency and intensity. We found a variety of response patterns in individual AL-units that clearly depended on stimulus frequency presented. While some units showed an ordinary rate code, others revealed a combinatorial pattern of an excitatory response to one frequency and an inhibitory response to another. The latter is reminiscent of glomerular responses to mechanosensory stimuli within the AL of honeybees.
In addition to the frequency-dependent responses, we found an increasing response strength accompanying increasing stimulus amplitude, suggesting a loudness effect as well. Taken together, our results support the idea of parallel processing of olfactory and mechanosensory information within an early-processing neural circuitry in insects. Studying different aspects of these mechanosensory-olfactory interactions at various levels, from behaviour to neural processing, represents a necessary next step and will contribute to a comprehensive understanding of the insect olfactory system as a whole.
This work was funded by the DFG grant (STR 1334/4-1) to MSB as part of the research unit 5424 ‘modulation in olfaction’.
