Spine Loss in Primary Somatosensory Cortex during Trace Eyeblink Conditioning

Abstract

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 ϳ15% 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.

Timing correlations between cerebellar interpositus neuronal firing and classically conditioned eyelid responses in wild-type and Lurcher mice

“…Thus, in our work, we have found different patterns of eyelid closing for delay and trace conditioning paradigms, although the shapes of those CRs were similar in WT and Lurcher mice. That shape was almost identical to those well described before in mice for delay 15 and trace 46 , 47 conditioning paradigms at early stages of the conditioning, when the position of the eyelid was recorded with technical procedures like the ones used here. Similar results for CR profiles were reported years ago in behaving cats 39 .…”

A method for combining multiple-units readout of optogenetic control with natural stimulation-evoked eyeblink conditioning in freely-moving mice

“…Likewise, recent studies have reported modified EBC training procedures in which the mice were head-fixed on a wheel. In these studies, the mice learned the association of blue light CS and airpuff US with a rate similar to our observation 8–10,20,41,45,51 .…”

Whisker-signaled Eyeblink Classical Conditioning in Head-fixed Mice

“…As mice appear to become distressed from restraint, this head-fixed preparation was developed to keep heads secure while reducing the amount of restraint required. While this preparation allows mice to ambulate on a cylindrical treadmill, others have also successfully collected behavioral data from head-fixed mice on a stable platform 24 .…”