Research
Modulation of sensory input to the olfactory bulb
Sensory input to the olfactory system is strongly modulated by presynaptic inhibition of transmitter release from olfactory receptor neurons. We are very interested in the functional properties of presynaptic inhibition and its role in odor coding. Presynaptic inhibition may prevent saturation of downstream circuitry during strong activation of receptor inputs, shape the strength of sensory input as a function of sniffing behavior, or allow for modulation of odor sensitivity as a function of behavioral state. Ongoing projects in the lab are exploring the mechanisms and function of presynaptic inhibition using a combination of synaptopHluorin and calcium imaging in vivo and in olfactory bulb slice preparations.
Olfaction as an active sense: Sniffing and odor coding
Animals actively acquire odor information by sniffing - a complex behavior that is heavily and rapidly modulated as a function of stimulus context, odor-guided task demands, and general behavioral state. We are interested in how the process of sniffing shapes the initial representation of odors as well as how odor information is processed postsynaptically. We approach this question using novel methods for imaging activity in the awake animal as it performs odor-guided tasks. We have found that sniffing shapes the temporal dynamics, the intensity, and even the identity of receptor neuron inputs to the olfactory bulb, thus playing a key role in shaping odor coding and - perhaps - odor perception. This raises many new questions, for example: how is odor information processed differently during different sniffing behaviors? what are the mechanisms by which the parameters of a sniff alter odor representations? how and when are different sniffing behaviors expressed by the animal, and how do these behaviors adaptively shape odor representations? We are addressing these questions using imaging in the awake and anesthetized animal, electrophysiological methods, behavioral assays and computational studies.
Functional recovery of olfactory maps after injury
Olfactory receptor neurons have a unique ability to regenerate even after a total loss of the receptor population, and to re-form axonal connections with their targets in the olfactory bulb. Regenerating neurons face the difficult problem of targeting specific glomeruli in the bulb, and the degree to which they are able to form appropriate connections and regenerate the functional odor representations that were present originally is unknown. Inappropriate targeting may explain dysosmias that can occur in humans after a large-scale loss of olfactory receptor neurons. The olfactory system is thus an interesting model for understanding how neurons re-form appropriate connections with their targets after injury and recovery. We are addressing this question by imaging maps of receptor input to glomeruli before, during and after the olfactory epithelium is lesioned and allowed to regenerate. Important questions are: how well and how precisely do functional odor maps recover? what rules govern the choice of glomerular targeting by receptor neurons? does odor experience play a role in the success of glomerular targeting by regenerated neurons? This work is being performed in collaboration with Jim Schwob at Tufts/NEMC.
Experience-dependent plasticity in odor representations
Mammalian sensory systems exhibit adaptive plasticity in response to the animal's environment and experience. This plasticity can include changes in the neurochemistry and anatomy of olfactory bulb glomeruli (especially in the expression of the neurotransmitter dopamine) and in the physiology of olfactory neurons. We are investigating how olfactory experience changes the representation of odors in the olfactory bulb, as observed using optical imaging techniques, and the corresponding changes in the behaviorally-observed perception of the quality and intensity of odors.