Stimulus and post stimulus olfactory representations in health and disease

Abstract

Sensory systems encode different stimuli features to generate optimal behavior In mammalian olfaction odorants of varying physicochemical properties are first represented as glomerular activity patterns in the olfactory bulb OB Within a glomerulus sensory information is relayed to OB output neurons mitral and tufted cells MTCs The firing activity of MTCs is modulated by the inhibitory neuronal network of OB thereby facilitating odor perception It is still unknown how these odor representations intersect with sniffing behavior to account for decision making time Using odorants belonging to different chemical classes we started probing glomerular activity patterns and sniffing behavior during decision making Mice trained to discriminate between different odor pairs increased their sniffing frequency at a fixed latency after odor onset independent of odor identity As sniffing frequency increased simple monomolecular odors were discriminated within 10 40 ms while complex binary mixtures took an additional 60 70 ms In vivo intrinsic imaging of glomerular activity patterns revealed that Euclidean distances between the activity patterns and odor discrimination times are inversely correlated Thus our findings suggest that the degree of neuronal processing necessary for odor discrimination is determined by the similarity and strength of glomerular activity patterns rather than sniffing behavior 1 Additionally odor representations formed during stimulus delivery dynamically change over time and persist even after odor cessation 2 We trained mice to perform discrimination tasks with varying stimuli durations to see how these odor representations during the stimulus and post stimulus period control olfactory learning and long term memory formation Reducing the stimulus duration for binary mixture discriminations led to impairments in learning and long term memory The calcium imaging data from anesthetized and awake animals identified stimulus duration dependent post odor activities in OB inhibitory interneurons D