Processing of complex host blends in the moth antennal lobe
The world is a cacophony of scent. Odors are often complex mixtures of compounds that create a spatially and temporally dynamic olfactory environment through which animals navigate. An animal’s ability to perform odor-mediated behavior requires the olfactory system to process and reliably identify complex volatile signals in a constantly changing background. The main challenge of my study was to reveal how complex odor information is processed in the insect olfactory system. In my thesis, I investigated odor blend processing at multiple levels in the olfactory system of the hawk moth, Manduca sexta. Using a novel multicomponent stimulus device and combined neuro-physiological techniques, I show that odor mixture processing in the moth brain is a highly combinatorial, non-linear integration process. In insects, the initial representation of odors detected by the antenna occurs in the first olfactory center of the brain, the antennal lobe (AL); the insect analog of the mammalian olfactory bulb. Afferent input (OSNs) is modified via interneuronal connections (LNs) and the resultant representation is carried by projection neurons (PNs, Output) to higher order brain centers. Accordingly, the antennal lobe representation of an odor mixture may either retain the single-odor information of blend components, or reveal non-linear interactions due to processing in the AL network. My combined physiological approach revealed high levels of across-fiber patterning within the antennal lobe establishing a unique blend percept separate from individual component identities as early as the first olfactory processing stage, the antennal lobe. Thus, analysis of blend input from sensory neurons (OSNs) cannot unambiguously predict AL output on any spatial or temporal scale. Combinatorial coding, shaped by the local network, may facilitate signal processing from a “noisy” periphery. Consequently, a minimum of broadly tuned receptors would be necessary to detect a multitude of complex blends.