The role of the lateral entorhinal cortex in olfactory information processing
Cognitive, Systems and Behavioural Neurobiology
Final Report Abstract
Olfactory cues provide rich information about the environment critical for behaviors as diverse as food seeking, social interactions, and predator avoidance. These behaviors depend on the identification of specific odors, as well as on the detection of odor concentration, particularly important for odor-guided navigation. In mammals, olfactory information is initially encoded by mitral cells in the olfactory bulb. Cells in the olfactory bulb project directly to the piriform cortex, the primary olfactory cortex, a region thought to be critical for odor identification. Although odorevoked activity in the olfactory bulb and piriform cortex have been described in great detail, much less is known about odor processing in higher brain areas. In this project, we explored odor coding in the lateral entorhinal cortex (LEC) in mice, a higher region that transmits information to the hippocampus which underlies odordependent memories and navigation. Therefore, we developed a closed-loop stimulation system for temporally precise odor presentation to awake, head-fixed mice combined with behavioral tests and electrophysiological recordings. We found that rapid odor-evoked activity within 50-100 ms after inhalation dominates in LEC. Further, we show that activity in the LEC is essential to discriminate odor identity and odor concentration, and mice are able to do both types of discrimination fast, showing a behavioral response after about 200 ms. Population analysis of LEC layer 2, the main input layer for olfactory information, showed that odor identity is encoded by the subset of neurons that increases their firing rate upon odor stimulation. Odor concentration in contrast is encoded by a change of spike timing, with faster response times and increased synchrony for higher concentrations. LEC layer 2 contains two classes of principal neurons, fan and pyramidal cells. We show that fan cells receive stronger inputs from the olfactory bulb and the piriform cortex resulting in a faster response time compared to pyramidal cells. Interestingly, fan cell response times are invariant to odor concentration, whereas pyramidal cell response times shift earlier with increasing concentration. This underlies the increased population synchrony in the LEC with increasing odor concentration, a temporal encoding that is transmitted downstream to the hippocampal area CA1. Together, these results reveal the unique odor processing by parallel subcircuits in LEC and highlight the importance of temporal coding in higher olfactory areas.
Publications
- Parallel pathways of odor processing in the lateral entorhinal cortex, Neuromatch 3.0 online conference, October 2020
Bitzenhofer, S. H.
- Parallel pathways for rapid odor processing in lateral entorhinal cortex: Rate and temporal coding by layer 2 subcircuits. bioRxiv (2021)
Bitzenhofer, S. H., Westeinde, E. A., Bear Zhang, H.-X., Isaacson, J. S.
(See online at https://doi.org/10.1101/2021.08.19.456942)
