Abstract
Most sensory systems are organized into parallel neuronal pathways that process distinct aspects of incoming stimuli. For example, in insects, second order olfactory projection neurons (PNs) target both the mushroom body (required for learning) and the lateral horn, proposed to mediate innate olfactory behavior. Mushroom body neurons encode odors in a sparse population code, which does not appear stereotyped across animals. In contrast the functional principles of odor coding in the lateral horn (LH) remain poorly understood. We have carried out a comprehensive anatomical analysis of the Drosophila LH counting >1300 neurons; combining genetic driver lines, anatomical and functional criteria, we identify 170 LH cell types. We then show that genetically labeled LHNs have stereotyped odor responses from one animal to the next. LHN tuning can be ultra-sparse (1/40 odors tested), but on average single LHNs respond to three times more odors than single PNs. This coding change can be rationalized by our observation that LHNs are better odor categorizers, likely due to pooling of input PNs that respond to different odors of the same category. Our results reveal some of the principles by which a higher sensory processing area can extract innate behavioral significance from sensory stimuli.
Footnotes
v2 includes some new analysis, but is mostly focussed on streamlining the presentation of the anatomical groundwork that precedes the main electrophysiological results and providing some additional discussion of recent results.
