Processing olfactory information of a single receptor type.

EZEQUIEL M. ARNEODO; KRISTINA PENIKIS; THOMAS BOZZA; DMITRY RINBERG

Encuentro; PEW annual meeting; 2015

Pew Charitable Trusts

Olfaction is an ideal system to study how the representation of a sensory stimulus is shaped from the receptor activation pattern and through the first processing layer before being conveyed to higher brain areas where decisions are made. Reasons for this are the compactness of this layer and the genetic tractability of the receptors.In the olfactory system, odor information is sampled and transduced by the olfactory sensory neurons (OSNs) in the nasal epithelium, and relayed to the brain in combinatorial patterns of activity. In the olfactory bulb (OB), axons of OSNs gather by genetic type into ~1000 glomeruli with stereotyped locations. Each glomerulus gives exclusive input to ~10 mitral/tufted (M/T) cells, which project widely to the cortex. In this way, the path that relays the activity of a particular receptor type comprises a single channel of information. The firing patterns of M/T cells are determined by the feed forward excitatory input from the glomeruli and the inhibitory activity of a vast network of interneurons in the OB. This suggests that M/T cells do not faithfully reproduce the OSNs representation of the stimulus: one of the fundamental questions of olfaction is what is the transformation that takes place.It has been shown that the activity of a single glomerulus is sufficient for behavior. The question that drives me is how the information of one of these single channels is represented at the output of the bulb, what it tells the higher brain areas about the activity of that particular receptor type and how relevant it is for the identification of an odor. To tackle these questions, I develop techniques that use optogenetics and multi-site extracellular electrophysiology in awake animals to identify M/T cells receiving input from an identified glomerulus and record their activities in response to stimuli for which the receptor?s response is well characterized (the receptor can be stimulated with odors or light). Since I can I record from cells that belong to a reduced and identified subset, every repetition of an experiment is outstandingly significant in determining how a single cell contributes to the information conveyed by the channel. By dissecting the system in these channels I can find mechanisms for coding sensory information that is sent to the cortex and used to make decisions.