Low-level mechanisms for processing odor information in the behaving animal

WACHOWIAK, M.; WESSON, D.W.; PÍREZ, N.; VERHAGEN, J.V.; CAREY, R.M.

San Francisco

Simposio; XV International Symposium on Olfaction and Taste; 2008

AChems

We typically think of sensory systems as generating faithfulrepresentations of external stimuli at initial, low-level stages of thenervous system and then performing increasingly complextransformations of these representations as information propagates tohigher levels. Likewise, the modulation of sensory codes duringbehavior – for example, as a function of behavioral context orattentional state – is typically thought to occur at higher nervoussystem levels. This talk will discuss recent findings from ourlaboratory demonstrating that, in the olfactory system, odorrepresentations in the behaving animal can be transformed at lowlevels – as early as the primary sensory neurons themselves - via avariety of different mechanisms. First, changes in odor samplingbehavior (i.e. – ‘sniffing’) can dramatically and rapidly alter primaryodor representations by changing the strength and temporal structureof sensory input to the olfactory bulb, effectively shaping whichfeatures of the olfactory landscape are emphasized and likely alteringhow information is processed by the olfactory bulb network. Second,neural substrates exist for presynaptically modulating the strength ofsensory input to the bulb as a function of behavioral state. Thesystems most likely to be involved in this modulation – cholinergicand serotonergic centrifugal inputs to the bulb – are linked toattention and arousal effects in other brain areas. Together, sniffingbehavior and presynaptic inhibition have the potential to mediate – orat least contribute to – sensory processing phenomena such as figuregroundseparation, intensity-invariance, and context-dependent andattentional modulation of response properties. Thus, ‘high-order’processing can occur even before sensory neurons transmitinformation to the brain.