Visualizing the engram: learning stabilizes odor representations in the olfactory network.
The nature of memory is a central issue in neuroscience. How does our representation of the world change with learning and experience? Here we use the transcription of Arc mRNA, which permits probing the neural representations of temporally separated events, to address this in a well characterized odor learning model. Rat pups readily associate odor with maternal care. In pups, the lateralized olfactory networks are independent, permitting separate training and within-subject control. We use multiday training to create an enduring memory of peppermint odor. Training stabilized rewarded, but not nonrewarded, odor representations in both mitral cells and associated granule cells of the olfactory bulb and in the pyramidal cells of the anterior piriform cortex. An enlarged core of stable, likely highly active neurons represent rewarded odor at both stages of the olfactory network. Odor representations in anterior piriform cortex were sparser than typical in adult rat and did not enlarge with learning. This sparser representation of odor is congruent with the maturation of lateral olfactory tract input in rat pups. Cortical representations elsewhere have been shown to be highly variable in electrophysiological experiments, suggesting brains operate normally using dynamic and network-modulated representations. The olfactory cortical representations here are consistent with the generalized associative model of sparse variable cortical representation, as normal responses to repeated odors were highly variable (∼70% of the cells change as indexed by Arc). Learning and memory modified rewarded odor ensembles to increase stability in a core representational component.
Division of Biomedical Sciences, Faculty of Medicine, and.
Amin M D
http://orcid.org/0000-0002-3776-3699
AM
Shakhawat
Division of Biomedical Sciences, Faculty of Medicine, and.
Ali
http://orcid.org/0000-0001-9125-0029
A
Gheidi
Division of Biomedical Sciences, Faculty of Medicine, and.
Qinlong
Q
Hou
Department of Psychology, Faculty of Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5, Canada.
Sandeep K
SK
Dhillon
Department of Psychology, Faculty of Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5, Canada.
Diano F
DF
Marrone
Department of Psychology, Faculty of Science, Memorial University, St. John's, Newfoundland A1B 3V6, Canada, and.
Carolyn W
http://orcid.org/0000-0001-8641-7998
CW
Harley
Division of Biomedical Sciences, Faculty of Medicine, and qi.yuan@med.mun.ca.
Qi
Q
Yuan
D000818:Animals; D000831:Animals, Newborn; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D007858:Learning / Q000502:physiology*; D008568:Memory / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism; D009474:Neurons / Q000502:physiology; D009812:Odorants; D009830:Olfactory Bulb / Q000502:physiology; D009833:Olfactory Pathways / Q000502:physiology*; D055696:Olfactory Perception / Q000502:physiology*; D066195:Piriform Cortex / Q000502:physiology; D051381:Rats
D051017:Apoptosis Regulatory Proteins; D009124:Muscle Proteins; C491788:Nol3 protein, rat
Arc; olfactory bulb; olfactory learning; piriform cortex