Spine loss in primary somatosensory cortex during trace eyeblink conditioning.
Classical conditioning that involves mnemonic processing, that is, a "trace" period between conditioned and unconditioned stimulus, requires awareness of the association to be formed and is considered a simple model paradigm for declarative learning. Barrel cortex, the whisker representation of primary somatosensory cortex, is required for the learning of a tactile variant of trace eyeblink conditioning (TTEBC) and undergoes distinct map plasticity during learning. To investigate the cellular mechanism underpinning TTEBC and concurrent map plasticity, we used two-photon imaging of dendritic spines in barrel cortex of awake mice while being conditioned. Monitoring layer 5 neurons' apical dendrites in layer 1, we show that one cellular expression of barrel cortex plasticity is a substantial spine count reduction of ∼15% of the dendritic spines present before learning. The number of eliminated spines and their time of elimination are tightly related to the learning success. Moreover, spine plasticity is highly specific for the principal barrel column receiving the main signals from the stimulated vibrissa. Spines located in other columns, even those directly adjacent to the principal column, are unaffected. Because layer 1 spines integrate signals from associative thalamocortical circuits, their column-specific elimination suggests that this spine plasticity may be the result of an association of top-down signals relevant for declarative learning and spatially precise ascending tactile signals.
Werner Reichardt Center for Integrative Neuroscience, Systems Neuroscience, Hertie Institute for Clinical Brain Research, Department of Cognitive Neurology, Graduate School of Neural and Behavioural Science, and.
Bettina
B
Joachimsthaler
Werner Reichardt Center for Integrative Neuroscience, Systems Neuroscience, Hertie Institute for Clinical Brain Research, Department of Cognitive Neurology.
Dominik
D
Brugger
Hertie Institute for Clinical Brain Research, Department of Cellular Neurology, German Center for Neurodegenerative Diseases, Eberhard Karls University, 72076 Tübingen, Germany.
Angelos
A
Skodras
Werner Reichardt Center for Integrative Neuroscience, Systems Neuroscience, Hertie Institute for Clinical Brain Research, Department of Cognitive Neurology, cornelius.schwarz@uni-tuebingen.de.
Cornelius
http://orcid.org/0000-0003-4725-473X
C
Schwarz
D000818:Animals; D003215:Conditioning, Eyelid / Q000502:physiology*; D049229:Dendritic Spines / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D059906:Neuroimaging; D010812:Physical Stimulation; D013003:Somatosensory Cortex / Q000166:cytology* / Q000502:physiology*; D014738:Vibrissae / Q000294:innervation / Q000502:physiology
barrel column; spine plasticity; trace eyeblink conditioning; trained mice; two-photon imaging