neural-circuits
Do ensembles form by excitability, not just synapses?
Open access · cc by · source: Europe PMC
Coactivating mouse L2/3 pyramids raised correlated firing with only small biphasic synaptic changes but large, persistent increases in intrinsic excitability.
How this study connects
Role on claims
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The block-and-reverse step is what makes excitability the candidate mechanism rather than a correlate.
In the one cellular study here, lasting change after coactivation was carried mainly by intrinsic excitability rather than synaptic weight. Presynaptic plasticity was small and biphasic — depression then potentiation — while coactivated mouse visual-cortex pyramidal cells showed strong lasting excitability gains (higher membrane resistance, lower spike threshold) that reversed when the membrane-resistance change was pharmacologically blocked.
Evidence for the claim as stated.
The cellular and human studies here cannot confirm one another, because they operate at incompatible levels of measurement. A mouse slice study can attribute lasting change to intrinsic excitability by blocking the membrane-resistance change; a human stimulation study recording force, connectivity or symptoms has no way to distinguish a synaptic account from an excitability one.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
The cellular and human studies here cannot confirm one another, because they operate at incompatible levels of measurement. A mouse slice study can attribute lasting change to intrinsic excitability by blocking the membrane-resistance change; a human stimulation study recording force, connectivity or symptoms has no way to distinguish a synaptic account from an excitability one.
Inspect source passages
Do ensembles form by excitability, not just synapses?
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Coactivation targeted L2/3 pyramids in mouse visual cortex of both sexes.
we co-activated layer 2/3 pyramidal neurons in brain slices from mouse visual cortex, in animals of both sexes
Excitability rose via higher membrane resistance and lower spike threshold.
increases in membrane resistance and reductions in spike threshold
Key findings
Coactivated cells increased correlated activity. Presynaptic plasticity was small and biphasic (depression then potentiation). Spontaneous EPSP frequency/amplitude rose even after single-cell stimulation. Strong lasting excitability gains (higher Rm, lower threshold) appeared and reversed when membrane-resistance changes were blocked pharmacologically—supporting an ‘iceberg’ model where subthreshold connections become suprathreshold.
Methodology
Replicated an in vivo optogenetic imprinting protocol in mouse visual-cortex slices, coactivating L2/3 pyramids and measuring pair correlations, EPSPs, membrane resistance, and spike threshold with whole-cell and perforated patch recordings.
Limitations
Slice coactivation may not fully recapitulate in vivo ensemble learning; human cortical ensembles and long-term behavior were not tested.
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