title: Learning enhances the relative impact of top-down processing in the visual cortex.
abstract: Theories have proposed that, in sensory cortices, learning can enhance top-down modulation by higher brain areas while reducing bottom-up sensory drives. To address circuit mechanisms underlying this process, we examined the activity of layer 2/3 (L2/3) excitatory neurons in the mouse primary visual cortex (V1) as well as L4 excitatory neurons, the main bottom-up source, and long-range top-down projections from the retrosplenial cortex (RSC) during associative learning over days using chronic two-photon calcium imaging. During learning, L4 responses gradually weakened, whereas RSC inputs became stronger. Furthermore, L2/3 acquired a ramp-up response temporal profile, potentially encoding the timing of the associated event, which coincided with a similar change in RSC inputs. Learning also reduced the activity of somatostatin-expressing inhibitory neurons (SOM-INs) in V1 that could potentially gate top-down inputs. Finally, RSC inactivation or SOM-IN activation was sufficient to partially reverse the learning-induced changes in L2/3. Together, these results reveal a learning-dependent dynamic shift in the balance between bottom-up and top-down information streams and uncover a role of SOM-INs in controlling this process.
authors.affiliation: Neurobiology Section, Center for Neural Circuits and Behavior, and Department of Neurosciences, University of California, San Diego, La Jolla, California, USA.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Makino
authors.affiliation: 1] Neurobiology Section, Center for Neural Circuits and Behavior, and Department of Neurosciences, University of California, San Diego, La Jolla, California, USA. [2] JST, PRESTO, University of California, San Diego, La Jolla, California, USA.
authors.forename: Takaki
authors.initials: T
authors.lastname: Komiyama
mesh_terms: D000818:Animals; D001245:Association Learning / Q000502:physiology*; D001522:Behavior, Animal / Q000502:physiology; D002118:Calcium; D005260:Female; D059330:GABAergic Neurons / Q000502:physiology; D007395:Interneurons / Q000502:physiology; D047569:Laser Scanning Cytometry; D008297:Male; D051379:Mice; D009474:Neurons / Q000502:physiology*; D013004:Somatostatin / Q000378:metabolism*; D014793:Visual Cortex / Q000166:cytology / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*
chemical_list: D013004:Somatostatin; D002118:Calcium