Each of these examples involves movement of the sense organs in order

to optimally sample an area or object of interest. Active stimulus sampling can profoundly affect patterns of sensory neuron activation and, consequently, the postsynaptic processing of sensory inputs. In addition, active sensing involves the coordination of “bottom-up” effects on sensory inputs with ‘top-down’ modulation Alectinib chemical structure of processing at multiple synaptic levels. Thus active sensation is a multilevel, systems-wide process affecting sensory system function. Olfaction, while not as extensively studied as other modalities, is in many respects an ideal model system for active sensing. First, for terrestrial vertebrates, olfactory sensation depends on stimulus acquisition by the animal; the inhalation of air into the nose is a necessary first step in olfaction. Second, mammals in particular have impressively complex behavioral repertoires for odorant sampling; this behavior—typically termed “sniffing”—is precisely and strongly modulated as a function of task demands, behavioral state and stimulus context (Welker, 1964, Wesson et al., 2009 and Youngentob et al., 1987). Finally, the olfactory system has in recent years matured into a highly tractable system in which its molecular, cellular, www.selleckchem.com/products/bmn-673.html and circuit-level organization can be examined, manipulated,

and integrated with behavioral experiments. A central thesis of this review is that the active components of olfactory sensation are closely woven with fundamental processes of olfactory system function at levels ranging from receptor expression patterns, sensory neuron response properties, circuit dynamics in the olfactory bulb and cortex, and centrifugal systems. As a result, the reliance of olfaction on transient, active sampling of odors is manifest even in reduced experimental preparations that are far removed from an actively sampling animal. Thus considering olfaction as an active sense is not only essential to understanding how this system works in the behaving animal, it is a useful framework for understanding olfaction

in many experimental contexts. A second point made here—and substantiated by examples from other sensory modalities—is that even descriptions of olfactory system function in the awake animal would benefit from considering sampling behavior through as a primary factor in shaping how the brain represents and processes olfactory input. In general, considering sensory systems in the context of active sensing provides an important avenue for understanding key principles of sensory system function in the behaving animal. In terrestrial vertebrates the olfactory epithelium is housed deep within the nasal cavity, such that inhalation of air is required for odorants to access olfactory receptor neurons (ORNs). Typically, this can only occur during the course of resting respiration or by the voluntary inhalation of air in the context of odor-guided behavior—i.e., sniffing.